Illustrated Guide to the Main Macroalgae of the Portuguese Continental Atlantic Coast

Pereira, Leonel

doi:10.3390/encyclopedia5040176

Open AccessField Guide

Illustrated Guide to the Main Macroalgae of the Portuguese Continental Atlantic Coast

by

Leonel Pereira

^1,2

¹

Centre for Functional Ecology: Science for People & Planet, Marine Resources, Conservation and Technology—Marine Algae Lab, Department of Life Sciences, University of Coimbra, 3000-456 Coimbra, Portugal

²

IATV—Instituto do Ambiente, Tecnologia e Vida, 3030-790 Coimbra, Portugal

Encyclopedia 2025, 5(4), 176; https://doi.org/10.3390/encyclopedia5040176

Submission received: 20 June 2025 / Revised: 19 September 2025 / Accepted: 4 October 2025 / Published: 20 October 2025

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Abstract

The Portuguese Atlantic continental coast serves as a biogeographic transition zone where numerous macroalgal species reach their distribution limits, making it an especially intriguing area for studying shifts in species distribution. This region features sandy beaches and rocky outcrops that serve as habitats for a diverse range of organisms, including macroalgae. This illustrated guide aims to provide a simple and accessible overview of some of the most representative macroalgae species found along this coastline, specifically those designed for non-specialists in seaweed identification. Rather than offering a detailed identification key, the guide introduces key aspects of macroalgae—such as pigment composition, taxonomic classification, morphology, branching types, habitat on rocky shores, and potential human uses—in a clear and approachable format. Each species is accompanied by a photographic image, a general morphological description, and information about its typical habitat. Additionally, icons indicate whether a species has potential human applications or is considered non-indigenous. Species are categorized into green, brown, or red macroalgae based on their color and morphological characteristics.

Keywords:

Rhodophyta; Chlorophyta; Heterokontophyta; biodiversity; ecology; uses

Graphical Abstract

1. Introduction

The coastal regions of Portugal host a rich and diverse macroalgal flora, shaped by Atlantic currents, ecological gradients, and historical biogeographic patterns. Despite this biological richness, there remains a gap in field-ready resources tailored specifically to the Portuguese Atlantic coast. This guide aims to fill that gap by providing an accessible, visually driven tool for the identification of macroalgae in this particular region [1].

While several identification guides exist at broader European or global scales, many are limited in geographic specificity, taxonomic updates, or usability in field conditions. Furthermore, taxonomic challenges—such as cryptic species, morphological plasticity, and shifting classifications—continue to complicate accurate identification. This work attempts to navigate these complexities, offering a regional perspective that integrates updated taxonomic insights and highlights species of some ecological and economic significance [2].

Although various identification guides for macroalgae exist at European and global scales, many are characterized by limitations that reduce their effectiveness in regional applications—especially along the Portuguese Atlantic coast. Some guides are outdated, relying on obsolete taxonomic frameworks, while others lack sufficient visual support, hindering field usability for non-specialists. Moreover, many resources either overlook region-specific species or present general descriptions that do not account for local morphological variations [3].

The selection of species featured in this guide was driven by several scientific and practical criteria, including ecological representativeness, regional abundance, taxonomic clarity, and relevance to biodiversity monitoring. Special attention was given to species frequently encountered along the Portuguese Atlantic coast, as well as those with key roles in habitat formation, nutrient cycling, or invasive dynamics. This approach ensures the guide remains both field-relevant and educational, serving stakeholders ranging from researchers and students [4].

Nonetheless, macroalgal identification is not without its uncertainties. Morphological plasticity—often influenced by environmental factors such as light exposure, wave action, or substrate type—can result in misleading visual traits. Additionally, cryptic species and recent taxonomic revisions challenge the reliability of traditional diagnostic features. To navigate these complexities, the guide incorporates updated nomenclature and highlights traits prone to variation or misinterpretation [5].

By grounding the guide in current trends of phycological research and biodiversity science—including biomonitoring programs, climate-related distribution shifts, and invasive species tracking—it contributes to broader efforts to assess and manage marine ecosystems [6]. The work aligns with national and European goals in coastal ecology and opens avenues for future refinement through citizen science and collaborative taxonomic updates [7].

A persistent challenge in macroalgal taxonomy lies in the high degree of morphological plasticity exhibited by many species, which can vary substantially depending on environmental conditions such as light exposure, water motion, and substrate type. This plasticity often obscures species boundaries and complicates identification based solely on external features [8]. These complexities underscore the need for regionally adapted guides that integrate morphological detail and offer updated nomenclature, with clear illustrations presented to support field and lab-based identification [9,10]. This field guide seeks to respond to these gaps, enhancing accuracy and accessibility in macroalgae identification along the Portuguese coast.

The ecological richness of the occidental Atlantic Portuguese coast is reflected in the high diversity of macroalgal species it supports, many of which are endemic or hold biogeographic significance within the Atlantic realm. This richness, however, exists alongside pronounced vulnerability—pressures from climate change, invasive species, and anthropogenic impacts threaten the integrity of coastal habitats and the delicate balance of macroalgal communities. As such, documenting and monitoring this biodiversity is not only scientifically valuable but also vital for informed coastal management [11,12,13].

By focusing on the Portuguese Atlantic continental coast, this guide contributes not only to local biodiversity monitoring but also to broader efforts in managing invasive species, supporting sustainable resource use, and fostering scientific literacy among students, researchers, and coastal stakeholders.

1.1. Overview of Macroalgal Diversity and Taxonomy

Macroalgae are macroscopic algae, visible to the naked eye, and exhibit a wide range of sizes—some species measure just a few centimeters, while others can grow to lengths of 50 m or more. They inhabit seawater and estuarine environments, typically anchoring themselves to hard substrates, particularly rocky surfaces [14].

There are many different species of macroalgae (between 7500 and 10,000 species) that also present a great diversity of shapes and colors. All macroalgae are primary producers, that is, they perform photosynthesis, because they contain chlorophylls and other accessory pigments. The coloration of a given species results from the combination of the different pigments presents in its cells [14].

1.2. Pigmentary Composition and Classification of Macroalgae

Macroalgae display a wide range of colorations, yet all contain chlorophyll. This pigment resides within small organelles called plastids, which are responsible for the green coloration found in most plants. The color of a macroalga is simply the visible expression of the unique combination of pigments present within its cells [14].

The phyla and classes of macroalgae are primarily defined, in practice, by their specific pigment composition. Macroalgae belong to the Domain Eukarya and are classified within the Kingdoms Plantae (green and red algae) and Chromista (brown algae), respectively. Although classification systems have varied significantly over time and among different authors, there is general consensus that can be elaborated as follows:

Green macroalgae (Chlorophyta phylum) could efficiently absorb red and blue color while reflecting green color. They are algae that contain chlorophyll a and b, carotenes and xanthophylls. Its reserve substance is starch and contains cellulose in its cell walls [12].

Brown macroalgae (Heterokontophyta phylum) are grouped in the class Phaeophyceae. These algae present a characteristic greenish-brown color due to the presence of chlorophyll a and c, tannins and carotenoids where fucoxanthin predominates, responsible for the brownish coloration [15].

Red macroalgae (Rhodophyta phylum) can efficiently absorb green and blue color and reflect slightly reddish radiation. Its photosynthetic pigments contain chlorophyll a, phycobilins (R-phycocyanin and R-phycoerythrin) and carotenoids (β-carotene, lutein and zeaxanthin) [16].

1.3. Morphological Types

The shape, or morphology, of the thallus (macroalgal body; plural: thalli) is a key feature used to distinguish between different macroalgae species. In addition, each species has a distinct consistency or texture to touch, which further aids in identification. This guide primarily relies on these characteristics.

Most thalli are erect, especially when submerged, although some species have prostrated thalli, forming thin disks or crust-like structures that adhere closely to the substrate. In some macroalgae, the thallus is divided into the frond—the upright portion—comprising the stipe and the blade, and a typically discrete attachment organ, which may appear as a small disk or a tuft of fine, elongated, colorless filaments known as rhizoids. Only large macroalgae possess a more robust attachment structure, made up of curved elements called a hapteron [9].

Some algae are filamentous, with fronds reduced to filaments composed of cells arranged end to end. These filaments may be either straight or branched. Typically, thalli are massive, meaning they possess a compact structure, although they can still exhibit a soft consistency and delicate texture [11].

The consistency and texture of thalli to touch are highly diverse. They can be cartilaginous (resembling cartilage), leathery or coriaceous (resembling leather), mucilaginous (similar to mucilage), spongy (like a sponge), among others. Some thalli, known as calcareous, have a rock-hard consistency due to their cells being impregnated with calcium carbonate [11].

While some thalli possess cylindrical axes, others are flattened or form hollow tubes. Certain thalli develop into monostromatic or polystromatic blades or sheets—composed of one or multiple layers of cells, respectively—and may be thin, moderately thick, or even coriaceous. These blades can be orbicular or elongated, undivided or segmented, lobed or deeply divided into laciniate forms resembling ribbons, straps, or belts. In some cases, they may be traversed by visible nerves or veins [14].

Branching Types

Another way of distinguishing the various species of macroalgae is to observe what kind of branching they have (Figure 1).

1.4. The Habitat of Rocky Shores

Macroalgae live generally immersed (inside the water) and fixed to a substrate. The richest sites on the macroalgae are the rocky coasts, but it is also common to find specimens on sandy coasts or bays exposed to the beat of the waves, which were detached from the substrate by the action of the sea and then dragged by the current. Several species also live in estuaries because they tolerate salinity gradients.

In rocky coastal areas, macroalgae living in the tidal range are subject to extreme ecological conditions (strong waves, sudden changes in temperature, salinity, sunshine, etc.). Their ability to adapt to the action of various ecological factors, in particular their ability to emerge (outside the water) by the descent of the tide, causes the different species to be distributed differently at different levels of the coastline (vertical zonation). Coastal zonation is divided into the following areas [9] (Figure 2):

(1) Supratidal Zone or Splash Zone: This is located between the mean level of high tide of the spring tides and the lower limit of terrestrial vegetation. This area is subject to splashes caused by the force of the waves, having a variable height, depending on the exposure to the waves of the coast. It is generally a poor area in number of species, and where marine lichens tend to predominate.

(2) Intertidal Zone: This is located between the upper and lower mean levels of the spring tides. It is the area where the ecological factors act more influence, being a place for multiple habitats, being the richest in number of species. Within this zone, the cycles of spring and neap tides determine a series of different horizons (intertidal zonation).

(3) Subtidal: This is located below the lowest level of the spring tides, extending to the level where the incident light is enough for the survival of the macroalgae. This zone is always immersed.

1.5. Non-Indigenous Algae on the Western Portuguese Coast

The western Portuguese coast has seen the introduction of several non-indigenous algal species (Figure 3), primarily through maritime activities and aquaculture. Among the most notable are Asparagopsis armata (Rhodophyta) and Sargassum muticum (Phaeophyceae), which have established themselves in intertidal and subtidal zones. These invasive species can outcompete native flora, alter habitat structures, and impact local biodiversity. Their presence highlights the need for ongoing monitoring and management strategies to mitigate ecological disruption and preserve the integrity of coastal marine ecosystems [12,13].

1.6. Uses

Nowadays, the macroalgae offers many possibilities for commercial use, with a wide range of applications. Many tons of macroalgae are harvested annually around the world, with China and Japan leading in consumption. However, macroalgae are utilized in many countries for a wide range of purposes, including human food, animal feed, agriculture, and medicine due to their therapeutic properties. The growing global demand for macroalgae has also led to their increasing exploitation in the industrial sector [14,15,16,19,20].

Potential uses of macroalgae by man include (see Figure 3).

(a) Human food and animal feed—this is certainly the best-known use worldwide. Sea vegetables, as macroalgae are often called, are a staple in the cuisine of many Eastern countries. In contrast, their use for self-consumption in Western countries was historically associated with poverty. Yet macroalgae stand in stark contrast to many modern processed foods—they are natural, nutrient-rich, and low in fat. Although approximately 50% of the dry weight of macroalgae consists of carbohydrates, humans lack the enzymes required to break down these long molecular chains. As a result, they are not absorbed by the digestive system and instead function like water-soluble fibers. Macroalgae are considered exceptional dietary supplements due to their high content of minerals, vitamins, and structural polysaccharides (fibers), which support intestinal transit and may help reduce blood cholesterol levels [21].

(b) Agriculture—the use of macroalgae as fertilizers is one of their oldest traditional applications. Certain species from the Corallinaceae family are also used to correct the pH of acidic soils, while simultaneously enhancing crop yields by supplying essential elements such as magnesium, strontium, boron, and iron. The two main macroalgal mixtures traditionally used as fertilizers are known as “Moliço” and “Sargaço” [22,23,24].

(c) Industry—the earliest industrial uses of macroalgae aimed to obtain calcium carbonate, produce soft drinks, and manufacture glass and soap. Macroalgae was also used for extracting iodine and certain dyes. Today, their industrial application is primarily focused on the production of phycocolloids—organic compounds that, when mixed with water, form colloidal systems capable of producing firm gels at room temperature [21].

(d) Pharmaceutical, Medicine, Thalassotherapy, Cosmetics, Dermatology—phycocolloids play a key role in the pharmaceutical industry due to their stabilizing and thickening properties, as well as their ability to yield compounds with antiviral, antibacterial, and antitumoral effects. Agar is notable for its medicinal applications, while carrageenans can inhibit the herpes virus and human papillomavirus (HPV), and are also used in hair care for their ability to bond with keratin. Alginic acid, extracted from brown algae such as Laminaria, Fucus, and Ascophyllum, is valued for its stability across varying pH and salinity levels, aiding in rapid healing and neutralizing heavy metals in cases of ingestion-related intoxication. Green macroalgae are traditionally used as anti-worm agents; red macroalgae serve as anticoagulants and are used to treat parasitic infections, gastritis, and diarrhea; and brown macroalgae are applied in the treatment of menstrual disorders, hypertension, skin diseases, syphilis, and gastric ulcers, also exhibiting anticoagulant properties [20,25].

2. Illustrated Guide

This guide provides the valid names and the respective authority, the order, the family, one of the synonyms, the common names (if any), the habitat [17,26], and a brief description of the main species present on the Portuguese coast.

The colors presented by algae are very varied and a superficial examination may lead to confusion, particularly when dealing with specimens of red and brown algae. How do you choose the right key right away?

For Chlorophyta (green algae) there is no difficulty, as they are algae, with a lighter or darker tone, but clearly green (Figure 4).

The diversity of colors is greatest in Phaeophyceae (brown algae); the color of these algae always has shades of brown or greenish brown (Figure 5).

Alongside samples that are easily recognizable, there are some red algae that can raise some doubts. In addition to the distinctly red hues, Rhodophyta can present various shades of brown and, in extreme cases, dark brown, almost black (Figure 6).

The illustrations in this guide are a means of identifying species by comparison. To confirm identification, consult references [9,17].

2.1. Green Macroalgae (Phylum Chlorophyta)

Filamentous (Figure 7).

Foliaceus (Figure 8).

Tubular (Figure 9).

Spongy (Figure 10).

2.2. Brown Macroalgae (Phylum Heterokontophyta, Class Phaeophyceae)

Filamentous (Figure 11).

Laminate/Foliaceus or Ribbons (Figure 12).

Cylindrical (Figure 13).

Big-Sized/Laminated (Kelps) (Figure 14).

2.3. Red Macroalgae (Phylum Rhodophyta)

Cylindrical/Filamentous (Figure 15).

Cylindrical/Hollow (Figure 16).

Cylindrical/Thick (Figure 17).

Flattened Thick (Figure 18).

Thin Laminate/Foliaceus or in Ribbons (Figure 19).

Calcareous (Figure 20).

3. Chlorophyta (Green Macroalgae)

3.1. Filamentous Green Macroalgae

Bryopsis plumosa (Hudson) C. Agardh 1823 (Figure 21).

Order: Bryopsidales; Family: Bryopsidaceae.

Synonym: Bryopsis thuyoides Kützing 1856.

Common name: Evenly Branched Mossy Feather Weed.

Habitat: On rocks, intertidal.

Description: B. plumosa is a small, feathery species of green seaweed. Its thalli are erect and feather-like, reaching up to 15 cm in height. It is easily recognized by its delicate, regularly arranged branches, which appear in two opposite rows along the central filament. The branch lengths gradually decrease from the base upward. The species typically exhibits a dark to mid-green coloration.

Figure 21. Bryopsis plumosa (Hudson) C. Agardh. Scale on image (b): 1 division = 1 mm; (a) underwater photo [13,17]; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Chaetomorpha aerea (Dillwyn) Kützing 1849 (Figure 22).

Order: Cladophorales; Family: Cladophoraceae.

Synonym: Chaetomorpha linum f. aerea (Dillwyn) Collins 1918.

Common name: Big green algae, Hair-shaped green algae.

Habitat: On rocks, intertidal.

Description: The plants are erect and attached, composed of vivid green filaments that can reach up to 10 cm in height. Basal cells measure up to 1 mm in length and bear spreading, lobed rhizoids, from which additional filaments may arise. The filaments are cylindrical or slightly constricted at the cross-walls, with cells becoming barrel-shaped in the distal (fertile) regions. Cell diameters range from 150 to 200 µm just above the basal cell to 200–300 µm in the distal portions, with cells measuring 0.4 to 1.0 times as long as they are broad. Reproductive cells are formed at the apical ends of the filaments; they are barrel-shaped and approximately as long as they are wide.

Figure 22. Chaetomorpha aerea. (a) Underwater photo; (b) detail. Reprinted from [17].

Chaetomorpha linum (O.F. Müller) Kützing 1845 (Figure 23).

Order: Cladophorales; Family: Cladophoraceae.

Synonym: Chaetomorpha aerea f. linum (O.F. Müller) Collins 1909.

Common names: Flax brick weed, Spaghetti algae, Sea emerald.

Habitat: On intertidal and supralittoral areas, including sandy areas, rocks, and tide pools. It can also be found in shallow, stagnant waters.

Description: Delicate green seaweed; also known as spaghetti algae, it grows as a filamentous loosely entangled mass. Usually free-floating, it may also be attached to rocks and shells. The filaments themselves are unbranched and usually between 5 and 30 cm in length. The unattached filaments are wiry, stiff and curled in appearance. It is bright light to dark green in color.

Figure 23. Chaetomorpha linum. (a) field photo; (b) detail. Reprinted from [17].; (c) Harvey’s illustration, reprinted from [18], public domain.

Cladophora laetevirens (Dillwyn) Kützing 1843 (Figure 24).

Order: Cladophorales; Family: Cladophoraceae.

Synonym: Cladophora affinis Schiffner 1933.

Habitat: On rocks, intertidal.

Description: The thallus is light to medium green, forming dense tufts ranging from 2 to 10 cm in height. Pseudo-dichotomous axes arise from a small cluster of rhizoids, which originate from cells in the basal region. Filaments exhibit only slight tapering and are branched from nearly every cell above the base, frequently bearing somewhat falcate, unilateral branchlets.

Figure 24. Cladophora laetevirens. Scale on images (a–d): 1 division = 1 mm; (a) field photo; (b–d) details; (e) apex with falcate and unilateral branchlets (40×), (f) rhizoids (40×). Reprinted from [17]; (g) Harvey’s illustration, reprinted from [18], public domain.

Cladophora prolifera (Roth) Kützing 1843 (Figure 25).

Order: Cladophorales; Family: Cladophoraceae.

Synonym: Conferva prolifera Roth 1797.

Common name: Green branched weed.

Habitat: In shallow pools on rough-water platforms and in the sublittoral.

Description: Species with coarse filaments that are either unattached or basally attached. These filaments typically measure less than 0.5 mm in width and range between 3 and 5 cm in length. Composed of a single row of often swollen cells, they are attached, when present, through a discoid base or rhizoidal outgrowths. The plant’s structure adds to its distinctive appearance and adaptability.

Figure 25. Cladophora prolifera. Scale on image (b): 1 division = 1 mm; (a) branch details (10×); (b) herbarium specimen. Reprinted from [17].

Derbesia tenuissima (Moris & De Notaris) P. Crouan & H. Crouan 1867 (Figure 26).

Order: Bryopsidales; Family: Derbesiaceae.

Synonym: Bryopsis tenuissima Moris & De Notaris 1839.

Habitat: Epilithic.

Description: The thallus is a dark green, tufted structure, reaching up to 10 mm in height. It emerges from an irregularly lobed, matted rhizoidal base and features numerous erect siphons that are sparsely branched. These siphons measure up to 120 µm in diameter at the base, gradually tapering to 50 µm near the tips. Double septa are occasionally observed at the bases of lateral branches. Chloroplasts are abundant, ranging from subspherical to lenticular in shape, with dimensions of 5–8 µm, each containing a pyrenoid. Sporangia are obovoid or pyriform, measuring up to 175 µm in length (including the pedicel) and 110–120 µm in diameter. They have a short pedicel and double septa at their base.

Figure 26. Derbesia tenuissima. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimens; detail. Reprinted from [17].

Lychaete pellucida (Hudson) M.J. Wynne 2017 (Figure 27).

Order: Cladophorales; Family: Cladophoraceae.

Synonym: Cladophora pseudopellucida C. Hoek 1963.

Common name: Pellucid green branched weed.

Habitat: Can be found in a variety of marine and freshwater habitats, including lakes, intertidal pools, and saline lakes.

Description: Filaments are rigid, erect, and setaceous, with a deep dark green coloration. They exhibit di-trichotomous branching, with very acute axils and upright branches. Articulations are many times longer than they are broad, and dissepiments are present only at the points where branches and ramuli fork.

Figure 27. Lychaete pellucida. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen. Reprinted from Ref. [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Rama rupestris (Linnaeus) Boedeker, M.J. Wynne & Zuccarello 2023 (Figure 28).

Order: Cladophorales; Family: Cladophoraceae.

Synonym: Cladophora rupestris (Linnaeus) Kützing 1843.

Common name: Common green branched weed, Slobán.

Habitat: Occurs on solid substrata across all littoral zones, with a preference for shaded locations in the lower littoral.

Description: Found on solid substrata throughout all littoral zones, with a preference for shaded areas in the lower littoral. Tolerant of reduced seawater salinity.

Figure 28. Rama rupestris. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen all reprinted from Ref. [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Rhizoclonium riparium (Roth) Harvey 1849 (Figure 29).

Order: Cladophorales; Family: Cladophoraceae.

Synonym: Rhizoclonium implexum (Dillwyn) Kützing 1845.

Common name: Rooting green thread weed.

Habitat: Marine, brackish, and some freshwater environments. It can grow on riverbanks, in estuaries, and on floating structures.

Description: The plants form mats or loosely arranged, fine entangled threads, measuring 50–100 mm in length. They are typically found in calm waters within the intertidal zone, growing on sandy or muddy substrates.

Figure 29. Rhizoclonium riparium (Roth) Harvey. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from Ref. [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Ulva clathrata (Roth) C. Agardh 1811 (Figure 30).

Order: Ulvales; Family: Ulvaceae.

Synonym: Enteromorpha clathrata (Roth) Greville 1830.

Common names: Bright green nori, Stone hair, Spiky tendrils.

Habitat: On rocks, intertidal and subtidal.

Description: The filaments are rigid, erect, and setaceous, with a deep, dark green coloration. They exhibit di-trichotomous branching, characterized by very acute axils and upright branches. The articulations are many times longer than they are wide, and dissepiments are present only at the points where the branches and ramuli fork.

Figure 30. Ulva clathrata. Scale on image (b): 1 division = 1 mm; (a) specimen detail; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

3.2. Laminar Green Algae

Gayralia oxysperma (Kützing) K.L. Vinogradova ex Scagel et al. 1989 (Figure 31).

Order: Ulotrichales; Family: Gayraliaceae.

Synonym: Ulva oxysperma Kützing 1843.

Common name: Ljus havssallt.

Habitat: A widely distributed marine species, occasionally found in weakly brackish water and freshwater streams near their confluence with the sea.

Description: Thalli form leafy, monostromatic blades ranging from a few centimeters to over one meter in length. Cells in the upper portion of the blade are polygonal and isodiametric, gradually becoming more elongated toward the base, where long rhizoidal projections are present in the holdfast region. In surface view, cells appear in groups of two or four. Each cell is uninucleate, containing a parietal chloroplast and a single prominent pyrenoid traversed by thylakoids.

Figure 31. Gayralia oxysperma. (a) field photo; (b) detail. Reprinted from [17].

Ulva australis Areschoug 1854 (Figure 32).

Order: Ulvales; Family: Ulvaceae.

Synonyms: Ulva laetevirens J.E. Areschoug 1854; Ulva pertusa Kjellman 1897.

Common name: Lacy sea lettuce,

Habitat: Found along coasts subject to strong to moderate wave action, typically occurring just above and below the low tide mark.

Description: U. australis is characterized by its smooth surface, distromatic blades, and lobed fronds. The thallus varies in color from dark green to light grass green and may be either free-floating or anchored by a single holdfast. Cells are irregularly arranged with rounded edges and exhibit a variety of shapes, including rectilinear, square, and pentagonal. The cells are irregularly arranged, with rounded edges, and display various shapes, including rectilinear, square, and pentagonal. Ulva rigida has sometimes been confused with this species.

Figure 32. Ulva australis. (a) Underwater photo; (b) specimens’ detail (all reprinted with permission from Ignácio Bárbara).

Ulva lactuca Linnaeus 1753 (Figure 33).

Order: Ulvales; Family: Ulvaceae.

Synonyms: Ulva fasciata Delile 1813; Ulva crassa Kjellman 1877; Ulva rotundata Bliding 1969.

Common names include Chicory sea lettuce, Green laver, Lettuce laver, Sea grass, Sea lettuce, and thin stone brick.

Habitat: Estuaries, Brackish waters.

Description: This species exhibits a vivid green coloration underwater, ranging from light yellowish green to deeper shades. When exposed at low tide or washed ashore, its color typically intensifies to a darker green. Out of water, it resembles a slimy lime-green mass; however, when submerged, it strikingly resembles young lettuce leaves. The seaweed is cellophane-thin, consisting of only two cell layers, and forms translucent sheets that vary in color from light yellowish green to dark green. Its soft frond is a single, irregularly shaped blade—somewhat round, with slightly ruffled and often torn edges. Scattered across the surface are small holes or perforations, contributing to its distinctive appearance. The frond is anchored to rocks by a small, nearly invisible, discoid holdfast and lacks a stipe. Although it can reach a diameter of 20 to 30 cm, it is often smaller, with larger sheets appearing slightly thicker than smaller ones.

Figure 33. Ulva lactuca. Scale on image (b): 1 division = 1 mm; (a) underwater photo; herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Ulva linza Linnaeus 1753 (Figure 34).

Order: Ulvales; Family: Ulvaceae.

Synonym: Enteromorpha linza (Linnaeus) J. Agardh 1883.

Common names: Doubled ribbon weed, Slender sea lettuce.

Habitat: On rocks, intertidal and subtidal, occasionally found under brackish conditions.

Description: A large, ribbon-like species of green seaweed that can grow up to 30 cm in length. The thalli are unbranched, often with frilled margins, and taper into a distinct, highly compressed stipe. The thallus is widest in the middle, narrowing toward the base, and may reach up to 5 cm in width. U. linza ranges in color from bright light green to dark green.

Figure 34. Ulva linza. (a) field photo; (b) detail. Reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Ulva rigida C. Agardh (Figure 35).

Order: Ulvales; Family: Ulvaceae.

Synonym: Ulva lactuca var. rigida (C. Agardh) Le Jolis 1863.

Common names: Green laver, Sea lettuce.

Habitat: On rocks, intertidal and subtidal.

Description: Dark green thallus, foliose, with highly variable size (up to 25 cm). It is anchored by a small basal disk. The morphology varies significantly depending on the environment and developmental stage, ranging from orbicular to umbilicate forms with wavy margins. The texture is firm, cartilaginous at the base, and can become almost leathery when dry. Occasionally, it is difficult to distinguish it from U. lactuca with the naked eye, although it is darker in color, thicker mostly in the middle part of the blade and of more rigid consistency. In cross section (observe under the microscope), both species have a structure formed by two layers of cells (distromatic), these are quadratic in U. lactuca and frankly elongated (2–3 times longer than wide) in the case of U. rigida.

Figure 35. Ulva rigida. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) general view; (c) cross section of the blade (distromatic) showing elongated cells (400×). Reprinted from [17].

3.3. Green Tubular and Vesiculosus Algae

Ulva compressa Linnaeus (Figure 36).

Order: Ulvales; Family: Ulvaceae.

Synonyms: Enteromorpha compressa (Linnaeus) Nees 1820.

Common names: Threadweed, Tapeweed.

Habitat: On rocks, mollusks or epiphytic; can also be found forming extensive mats on rocky substrates with the presence of sand; upper- and mid-intertidal.

Description: The thallus is yellowish-green, tubular, and typically compressed and wrinkled, ranging from 10 to 20 cm in height. The tubes narrow at the base and progressively widen toward the apex, which is obtuse and often torn. Thalli are prolific at the base, with entire margins, and may sometimes resemble a bowl-like structure. Entanglement is common, making it difficult to distinguish individual specimens. The presence or absence of branching fronds is the most useful gross morphological characteristic for distinguishing Ulva compressa from Ulva intestinalis, the latter typically being unbranched. However, ambiguity arises as low salinity or salinity shock can induce branching in U. intestinalis.

Figure 36. Ulva compressa. Scale on images (b,c): 1 division = 1 mm; (a) field photo; (b) general view, (c) branching frond (d) cross section of the tubular thallus (100×). Reprinted from [17].

Ulva intestinalis (Figure 37).

Order: Ulvales; Family: Ulvaceae.

Synonym: Enteromorpha intestinalis (Linnaeus) Nees 1820.

Common names include: Gutweed, Grass kelp, Hollow green nori, Hollow green weed, Tubular sea lettuce, and Seagrass.

Habitat: At all levels of the shore, occurring in a wide range of habitats, where suitable support is available, it will grow on rocks, mud, sand and in rock pools; it is abundant in brackish water.

Description: Thallus bright grass-green, tubular, which can reach large dimensions (up to 1 m). It grows from a small discoid base and is slightly stiped; it progressively widens in an inflated tube, irregularly constricted, of characteristic intestine-like appearance, which gives its name to the species. The tube is usually simple, typically unbranched. The presence or absence of branching fronds is the most useful gross morphological characteristic for distinguishing Ulva compressa from Ulva intestinalis, with the latter typically being unbranched.

Figure 37. Ulva intestinalis. Scale on image (d): 1 division = 1 mm; (a,b) field photos; (c) general view; (d) frond with an intestine-like appearance; (e) cross section of the tubular thallus (100×). Reprinted from [17].

Ulvaria obscura (Kützing) Gayral ex Bliding 1969 (Figure 38).

Order: Ulvales; Family: Ulvaceae.

Synonym: Monostroma obscurum (Kützing) J. Agardh 1883.

Habitat: From the tidal zone to the sublittoral.

Description: Thallus widely bladed, similar to that of another Ulva, turning brown on dying. monostromatic blade. Present in sublittoral, at 3–17 m depth, everywhere. It does not occur often. Bipolar species.

Figure 38. Ulvaria obscura. Scale on image (b): 1 division = 1 mm; (a) Underwater photo; herbarium specimens; (b) herbarium specimens; (c) observation under the microscope (40×) of the cross section of the blade, where it can be seen that it consists of only one layer of cells (all reprinted with permission from Ignácio Bárbara).

Valonia utricularis (Roth) C. Agardh 1823 (Figure 39).

Order: Cladophorales; Family: Valoniaceae.

Synonym: Valonia incrustans Kützing 1843.

Habitat: Found in the infralittoral zone (1–35 m depth), growing epilithically on coral substrates or within seagrass meadows.

Description: The thallus is an aggregate structure, both prostrate and partially erect, reaching 1–3 cm in height. It is translucent, displaying colors ranging from bright green to deep dark green, and consists of branched filaments made up of macroscopic cells.

These cells are firm but not densely packed, exhibiting a saccate form, which can vary between spherical, cylindrical, oblong-clavate, and pyriform shapes. They are arcuate, measuring 3–7 mm in diameter and 5–20 mm in length. Branching occurs irregularly from all sides of the parent cell. The plant attaches to surfaces via minute branched rhizoids that emerge from small basal cells. When dried, the plants adhere tightly to paper.

Figure 39. Valonia incrustans. (a) Field photo: (b) detail; (c) microscopic observation (20×). Reprinted from [17].

3.4. Sponge Green Algae

Codium adhaerens C. Agardh 1822 (Figure 40).

Order: Bryopsidales; Family: Codiaceae.

Synonym: Spongodium adhaerens (C. Agardh) Lenormad ex Duby 1830.

Habitat: A perennial seaweed found on both exposed and sheltered shores, typically in low-light conditions. It is most commonly located on vertical rock faces and within crevices.

Description: The thallus is spongy and prostrate, displaying a vibrant green hue and forming an irregularly shaped, carpet-like layer firmly attached to the substrate. It consists of a network of entangled coenocytic filaments, with a surface lined by narrow, elongated utricles that are difficult to separate. The texture is firm yet gelatinous, offering a smooth and pleasant feel.

Figure 40. Codium adhaerens. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) specimen detail; (c) microscopic observation of the utricles (100×). Reprinted from [17]; (d) Harvey’s illustration, reprinted from [18], public domain.

Codium tomentosum Stackhouse (Figure 41).

Order: Bryopsidales; Family: Codiaceae.

Synonym: Codium dichotomum S.F. Gray 1821.

Common names: Sponge weed, Velvethorn.

Habitat: On rocks, mid-intertidal (tide pools), lower-intertidal and subtidal.

Description: Light green to dark green, spongy, dichotomously branched, formed by anastomosed filaments of rounded section (flattened at the forks of the branches), to 40 cm in length. Fixed by a spongy disk. Utricles smooth and piriform with rounded apex; gametangia oblong to fusiform, formed on small peduncles that appear in the half part of the utricle.

Figure 41. Codium tomentosum. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) general view; (c) bifurcation of the flattened branches; (d) (utricle (*) with gametangia (**) (100×). Reprinted from [17].

4. Heterokontophyta, Phaeophyceae (Brown Macroalgae)

4.1. Filamentous Brown Macroalgae

Cladostephus spongiosus (Hudson) C. Agardh (Figure 42).

Order: Sphacelariales; Family: Cladostephaceae.

Synonym: Cladostephus densus Kützing 1856.

Common name: Hairy sand weed.

Habitat: On rocks and on sandy rock pools, from the mid-intertidal to subtidal.

Description: Dark greenish-brown thallus of rigid consistency, up to 20–30 cm high. Cylindrical axes are divided in an irregularly dichotomous manner, and which present verticils/whorls of short filamentous branches, upwards curved (sickle-shaped) and pointed. The lower part of the axis is usually bare and the distance between the whorls decreases as it ascends, forming an almost continuous coating that gives the alga a spongy touch. Discoid holdfast.

Figure 42. Cladostephus spongiosus. Scale on images (a–c): 1 division = 1 mm; (a) field photo; (b) general view; (c) branch detail; (d) whorls curved upwards and pointed (40×). Reprinted from [17].

Ectocarpus siliculosus (Dillwyn) Lyngbye 1819 (Figure 43).

Synonym: Conferva siliculosa Dillwyn 1809.

Order: Ectocarpales; Family: Ectocarpaceae.

Habitat: Found on various firm substrate near or just below the low-tide mark; later often becomes free-floating. Also occurs epiphytically.

Description: Plants are tufted, typically measuring only one to a few centimeters in height, though they may exceptionally reach up to 20 cm. Axes are freely branched, with no distinguishable main axis. Filaments are up to 30 μm in diameter and taper toward the apices, sometimes forming terminal pseudo-hairs.

Figure 43. Ectocarpus siliculosus. Scale on image (a): 1 division = 1; (a) herbarium specimen, reprinted from [17].; (b) Harvey’s illustration, reprinted from [18], public domain.

Halopteris filicina (Grateloup) Kützing 1843 (Figure 44).

Order: Sphacelariales; Family: Stypocaulaceae.

Synonym: Sphacelaria filicina (Grateloup) C. Agardh 1824.

Common name: Sea Fern Weed.

Habitat: A marine species found on rocks in tide pools, ranging from the mid-intertidal to shallow subtidal zones. Its occurrence is sporadic, though it can be locally common.

Description: A soft, limp, and slippery seaweed with smooth, somewhat flattened branches. Coloration varies and may appear red, green, brown, or nearly black. Size and shape are highly variable, with branches measuring 0.5 to 5 mm in width and 2 to 30 cm in length. Branching may be sparse or dense.

Figure 44. Halopteris filicina. Scale on image (a): 1 division = 1 mm; (a) photo of a specimen with scale; (b) observation under a microscope (10×) (all reprinted with permission from Ignácio Bárbara).

Halopteris scoparia (Linnaeus) Sauvageau (Figure 45).

Order: Sphacelariales; Family: Stypocaulaceae.

Synonym: Stypocaulon scoparium (Linnaeus) Kützing.

Common names: Sea flax, Taggtofs.

Habitat: On rock and epiphytic, rock pools with sand deposition, mid- and low-intertidal and shallow subtidal.

Description: Dark greenish-brown thallus to 10–15 cm high, compact and rough to touch. The main axis, whose spongy basal part is fixed by rhizoids, branches in all directions. During winter, the more abundant branches give the thallus an arbuscular aspect, while in summer it forms a kind of inverted cones superimposed with the appearance of shaving brushes. The last branches are pinnate.

Figure 45. Halopteris scoparia. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) general view; (c) apexes (40×); (d) detail of the branches (40×). Reprinted from [17].

Hincksia granulosa (Smith) P.C. Silva 1987 (Figure 46).

Order: Ectocarpales; Family: Acinetosporaceae.

Synonym: Ectocarpus granulosus (Smith) C. Agardh 1828.

Habitat: Rare, found in lower eulittoral turfs.

Description: This species forms low turf alongside other filamentous algae or as an epiphyte. The thallus ranges from 0.5 to 3 cm in height, occasionally reaching up to 6 cm, and consists of a tuft of branching uniseriate filaments, each cell containing numerous discoid plastids. Growth appears diffuse, with no clearly defined meristematic regions. The axes exhibit profuse branching up to four orders, with each successive order becoming narrower, and all filaments gradually tapering. Fully elongated cells of the primary axis are barrel-shaped and nearly isodiametric, measuring 50–60 µm in diameter and 70–80 µm in length. Terminal filaments are approximately 15 µm in diameter. The main branches predominantly display opposite branching, while later branches vary between irregular, secund, and occasionally recurved patterns. The proximal regions of the main branches are corticated by downward-growing rhizoids, which anchor the structure to the substratum. Plurilocular sporangia are sessile, though occasionally borne on a single-celled pedicel, and are positioned on the adaxial side of the later branch orders. These structures are ovoid, generally symmetrical, curve upwards, and measure approximately 90 µm in length and 60 µm in diameter.

Figure 46. Hincksia granulosa. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen; (b) detail of the opposite branches (40×), reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Hincksia hincksiae (Harvey) P.C. Silva 1987 (Figure 47).

Order: Ectocarpales; Family: Acinetosporaceae.

Synonym: Ectocarpus hincksiae Harvey 1841.

Habitat: Found in lower eulittoral turfs.

Description: The erect thallus of this widespread genus is composed of uniseriate, branched filaments, with diffuse intercalary growth. Chloroplasts are parietal, disk-shaped, and numerous within each cell, each containing a single pyrenoid. True phaeophycean hairs are absent. Branching patterns within the genus exhibit variability, ranging from secund arrangements to species with scattered or opposite branching. The positioning of the often-sessile plurilocular sporangia also varies. In some species, they arise through the transformation of short laterals extending from the adaxial side of the supporting lateral, giving a serrated appearance. However, they may also be present on the main axis.

Figure 47. Hincksia hincksiae. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from [17]; (b) unilateral branching with several plurilocular sporangia (40×); (c) detail of the plurilocular sporangia (100×) (reprinted with permission from Ignácio Bárbara).

4.2. Laminate/Foliaceus or Ribbons Brown Macroalage

Ascophyllum nodosum (Linnaeus) Le Jolis 1863 (Figure 48).

Order: Fucales; Family: Fucaceae.

Synonym: Fucus nodosus Linnaeus 1753.

Common names: Knotted wrack; Egg wrack, Yellow weed.

Habitat: On rocks of mid- to lower intertidal.

Description: This brown seaweed, closely related to Fucus, develops a single central bladder within its long, flattened, strap-like fronds. These fronds hang downward, draping over sheltered intertidal rocks. Numerous fronds arise from the base, and the plant typically regenerates new ones from this region when older fronds are damaged. There is evidence that some clumps may be over 400 years old, and possibly even older. Ascophyllum is currently restricted to the North Atlantic basin. Its fronds are commonly used as packing material for shellfish harvested in the region, and when discarded, they may establish and continue to grow.

Figure 48. Ascophyllum nodosum. Scale on image (b): 1 division = 1 mm; (a) field photo, (c) herbarium specimen, reprinted from [17]; Harvey’s illustration, reprinted from [18], public domain.

Cutleria multifida (Turner) Greville 1830 (Figure 49).

Order: Tilopteridales; Family: Cutleriaceae.

Synonym: Zonaria multifida C. Agardh 1820.

Common name: Cutler’s many cleft weed.

Habitat: On rocks, usually isolated, subtidal to 10 m.

Description: Thalli are erect, light yellow-brown to olive-brown in color, flattened and membranous, with smooth margins. They are deeply incised, exhibiting repeatedly irregular forking that forms linear to wedge-shaped segments, gradually narrowing toward the tip. The dissected apices are fringed with tufts of hair-like filaments. The plant lacks a stipe and is anchored by a rhizoidal, discoid holdfast.

Figure 49. Cutleria multifida. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Desmarestia ligulata (Stackhouse) J.V. Lamouroux 1813 (Figure 50).

Order: Desmarestiales; Family: Desmarestiaceae.

Synonym: Herbacea ligulata Stackhouse 1809.

Common names: Color changer, Desmarest’s flattened weed, Sea sorrel.

Habitat: Found on rocks in pools within the lower intertidal zone; however, it is primarily subtidal, often abundant down to depths of 15 m.

Description: This species of brown seaweed resembles a flattened cactus. A flat main axis, approximately 2 cm wide and featuring a prominent midrib, arises from a discoid holdfast. Numerous thinner, oppositely arranged, flat lateral branches extend from the main axis. D. ligulata grows from the lower intertidal to subtidal zones and can reach up to 80 cm in length. This species produces and stores sulfuric acid, which is released when the algae are stressed—breaking down their own tissues as well as those of nearby seaweed.

Figure 50. Desmarestia ligulata. Scale on image (c): 1 division = 1 mm; (a) Underwater photo: (b) detail; (c) herbarium specimen, reprinted from [17]; (d) Harvey’s illustration, reprinted from [18], public domain.

Dictyopteris polypodioides (A.P. De Candolle) J.V. Lamouroux (Figure 51).

Order: Dictyotales; Family: Dictyotaceae.

Synonyms: Dictyopteris membranacea Batters 1902; Dictyopteris ambigua (Clemente) Cremades 1990.

Common name: Netted wing weed.

Habitat: Lower-intertidal and mostly subtidal.

Description: Yellowish when juvenile, growing darker brown with age, translucent, flat and leaf-like, to 30 cm long and 2–3 cm broad, dichotomously forked, with a prominent midrib extending to the apices. In older specimens, the midrib is often the only visible basal structure. Margins are smooth, except near the base where they may be somewhat serrated. Apices are rounded, occasionally cleft. Thick and fibrous basal disk. Newly collected specimens have an unpleasant odor.

Figure 51. Dictyopteris polypodioides. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen; (c) blade detail with prominent midribs. Reprinted from [17].

Dictyota dichotoma (Hudson) J.V. Lamouroux (Figure 52).

Order: Dictyotales; Family: Dictyotaceae.

Synonym: Dictyota rotundata J.V. Lamouroux 1809.

Common names: Divided net weed, Brown fan weed.

Habitat: On rocks and epiphytic, mid- and lower-intertidal and subtidal.

Description: Fronds upright, delicate, transparent, olive green to light brown, yellowish or greenish brown, iridescent sometimes, up to 30 cm long; reproductive structures scattered on the blade; fixed to the substrate by colorless rhizoids. Fronds flattened, ribbon-like fronds repeatedly forking dichotomously in a plane, repeatedly with the same length in a very regular manner, in blades of parallel margins, sometimes spiraled; without central nerve, width constant from base to tip, or only slightly narrowing (of variable width up to 1 cm); rounded or slightly pointed apices (usually bifid).

Figure 52. Dictyota dichotoma (Hudson) J.V. Lamouroux (Phaeophyceae). Scale on images (b–d): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimens; (c) blade apexes; (d) reproductive structures scattered on the blade. Reprinted from [17].

Dictyota spiralis Montagne 1846 (Figure 53).

Order: Dictyotales; Family: Dictyotaceae.

Synonym: Dilophus spiralis (Montagne) Hamel 1939.

Common names: Ribbon algae; Spiral algae.

Habitat: Near the surface of rocks, also as an epiphyte.

Description: Thallus is bushy and erect, with ribbon-like lamina segments that fork regularly and spiral around the longitudinal axis. The tips are straight and pointed. The thallus measures 10–20 cm in length, brown in color with tips appearing in a lighter shade.

Figure 53. Dictyota spiralis Montagne. Scale on image (c): 1 division = 1 mm; (a) underwater photo; (b) detail; (c) herbarium specimen. Reprinted from [17].

Padina pavonica (Linnaeus) Thivy 1960 (Figure 54).

Order: Dictyotales; Family: Dictyotaceae.

Synonym: Padina mediterranea Bory 1827.

Common names: Peacock’s Tail.

Habitat: Found on rocks in sheltered locations near the surface, extending to depths of up to 20 m.

Description: The frond is thin and leafy—initially flat and entire in young specimens but often becoming concave or nearly funnel-shaped as it matures, with a laciniate or irregularly lobed margin. The inner (upper) surface is coated with a thin layer of slime, while the outer (lower) surface displays banded zones of light brown, dark brown, and olive green. Small, fine hairs form concentric lines spaced 3–5 mm apart, extending from the outer margin down the colored surface of the fronds.

Figure 54. Padina pavonica. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Greville’s illustration, reprinted from [27].

Petalonia fascia (O.F. Müller) Kuntze 1898 (Figure 55).

Order: Ectocarpales; Family: Scytosiphonaceae.

Synonym: Scytosiphon fascia (O.F. Müller) P. Crouan & H. Crouan 1867.

Common names: Broad Leaf Weed, Sea Petals.

Habitat: Typically thriving on stones and shells in calm, shallow pools—especially within harbors—this species is most commonly observed during spring and early summer.

Description: The thallus consists of erect, light to dark brown, dorsoventrally flattened laminae arising from a holdfast, either singly or in clusters. Laminae range from linear to broadly lanceolate or nearly elliptical, narrowing abruptly or gradually toward the base and merging into a short stipe. The stipe is only slightly narrowed at the tip, which is rounded and often frayed. The thallus is undivided, membranous, and thin in young specimens, becoming leathery and tough with age, with smooth and occasionally undulating margins. This species is highly polymorphic, particularly with respect to thallus width.

Figure 55. Petalonia fascia. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Phyllariopsis brevipes subsp. pseudopurpurascens Pérez-Cirera, Cremades, I. Bárbara, & M.C. López 1991 (Figure 56).

Order: Tilopteridales; Family: Phyllariaceae.

Habitat: Found in marine environments, typically in cooler waters. The exact distribution can vary, but it is generally associated with rocky shores and subtidal areas where it can attach to substrates. This species requires another species, Mesophyllum lichenoides (Rhodophyta), as substrate.

Description: This species is characterized by short-stalked thalli and a pseudoparenchymatous structure, typical of brown algae. Its pigmentation is predominantly brown, though the subspecies name, pseudo-purpurascens, hints at a reddish or purplish hue visible under specific conditions. Variations in morphology and anatomy exist, and reliable identification often necessitates microscopic analysis and comparison with reference specimens.

Figure 56. Phyllariopsis brevipes subsp. Pseudopurpurascens. (a) underwater photo, reprinted from [17]; (b) general view (reprinted with permission from Ignácio Bárbara).

Taonia atomaria (Woodward) J. Agardh 1848 (Figure 57).

Order: Dictyotales; Family: Dictyotaceae.

Synonym: Dictyota atomaria (Woodward) Greville 1830.

Common name: Dotted Peacock Weed.

Habitat: Found in pools on rocky and sandy substrata in semi-wave-exposed environments, extending to depths of up to 10 m.

Description: The thallus is flat and leaf-like, reaching up to 300 mm in length (typically 100–150 mm) and 10–40 mm in width. Fronds are thin, translucent, and range in color from olive to yellow-brown. They are irregularly forked and laciniate, lacking a midrib. Reproductive structures are characteristically arranged in wavy bands.

Figure 57. Taonia atomaria. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

4.3. Cylindrical Brown Macroalgae

Bifurcaria bifurcata R. Ross (Figure 58).

Order: Fucales; Family: Sargassaceae.

Synonym: Ascophylla tuberculatum Kuntze 1891.

Common names: Brown tuning fork weed, Brown forking weed.

Habitat: On rocks, sand tolerant, intertidal tide pools, lower intertidal and shallow subtidal.

Description: Yellowish-brown (dark colored by dissection), leathery consistency, in the form of cylindrical strings, sub-dichotomic (in which the two branches of the dichotomy acquire different dimensions, giving to the frond a characteristic appearance, as in a zigzag) of 3 to 4 mm in diameter and up to 30–40 cm in length, fixed by a crawling and branched axis fitted with adhesive disks. The receptacles at the apices (5–8 cm in length and slightly larger in diameter than the axes that carry them) have small obtuse protrusions on their surface, with hermaphrodite conceptacles.

Figure 58. Bifurcaria bifurcata. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) field photo; (c) receptacles at the apexes (*). Reprinted from [17].

Chorda filum (Linnaeus) Stackhouse 1797 (Figure 59).

Order: Chordales; Family: Chordaceae.

Synonym: Polyides filum (Linnaeus) Chevalier 1836.

Common names: Bootlace weed, Cat gut, Dead men’s ropes, Mermaid’s fishing line, Mermaid’s line, Mermaid’s tresses, Sea lace, Sea laces.

Habitat: Found in rock pools on the lower shore and in the sublittoral zone down to depths of 5 m. It is most commonly encountered in sheltered bays, where it attaches stones and shells.

Description: This species is characterized by its slender, cord-like fronds, which have a diameter of just 5 mm. These fronds are hollow, smooth, and unbranched, capable of reaching lengths of up to 8 m. The seaweed anchors itself to the substratum through a small, disk-shaped holdfast. As an annual species, it thrives during the warmer months but disappears in winter.

Figure 59. Chorda filum. (a) Field photo; (b) detail, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Cystoseira foeniculacea (Linnaeus) Greville 1830 (Figure 60).

Order: Fucales; Family: Sargassaceae.

Synonym: Abrotanifolia foeniculacea (Linnaeus) Stackhouse 1809.

Common name: Bushy feather wrack.

Habitat: Occurs in eulittoral pools and sheltered places.

Description: Caespitose macroalga reaching up to 30 cm in height, attached to the substrate by a wide, irregular basal disk. Axes grow up to 10 cm tall and possess a circular cross section, measuring up to 5 mm in diameter. They are typically spinose, bearing small scars from dehisced primary branches. The apices of the axes are inconspicuous and bear small spines.

Figure 60. Cystoseira foeniculacea. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Cystoseira humilis Schousboe ex Kützing 1860 (Figure 61).

Order: Fucales; Family: Sargassaceae.

Synonym: Cystoseira canariensis Sauvageau 1912.

Habitat: Occurs in eulittoral pools and sheltered places.

Description: This species is characterized by distinct basal and apical regions, along with the presence of catenate pneumatocysts (air vesicles). In mature specimens, the main axis elongates, and the primary lateral branches extend proportionally. The lower portions of these branches are strongly flattened into foliar expansions or basal leaves. Fertile regions, known as receptacles, contain conceptacles and are typically located at the tips of the branches. The catenate pneumatocysts aid in buoyancy, helping the organism remain erect and float in strong currents.

Figure 61. Cystoseira humilis. Scale on images (c): 1 division = 1 mm; (a) underwater photo; (b) detail; herbarium specimen. Reprinted from [17].

Ericaria selaginoides (Linnaeus) Molinari & Guiry 2020 (Figure 62).

Order: Fucales; Family: Sargassaceae.

Synonym: Cystoseira tamariscifolia (Hudson) Papenfuss 1950.

Common names: Bushy rainbow wrack; Rainbow bladderweed

Habitat: Found in rockpools and on the lower shore, this species grows on both rocky substrates and gravelly flats.

Description: This bushy seaweed typically reaches 30–45 cm in length, though it can grow up to 60 cm. It features a cylindrical frond and branches irregularly. The reproductive bodies, located at the ends of the branches, are elongated, oval, and spiny. Small air bladders are usually present just below these reproductive structures. E. selaginoides is olive green in color, appearing almost black when dry. Underwater, it displays a striking blue-green iridescence.

Figure 62. Ericaria selaginoides. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Fucus ceranoides Linnaeus 1753 (Figure 63).

Order: Fucales; Family: Fucaceae.

Synonym: Hesperophycus harveyanus (Decaisne) Setchell & N.L. Gardner 1910.

Common names: Estuary wrack, Horned wrack.

Habitat: Restricted to estuaries and areas near freshwater streams along the shore.

Description: This large brown intertidal seaweed is typically found in brackish environments such as estuaries or near freshwater inflows. F. ceranoides lacks air bladders, but the sides of its fronds are often noticeably inflated, giving them a distinctive appearance.

Figure 63. Fucus ceranoides. (a) field photo; (b) detail, reprinted from [17]; (c) original illustration from the author.

Fucus serratus Linnaeus 1753 (Figure 64).

Order: Fucales; Family: Fucaceae.

Synonym: Halidrys serrata (Linnaeus) Stackhouse 1809.

Comon names: Saw Wrack, Serrated wrack, Serrated Wrack, Toothed Wrack.

Habitat: Occurs on firm substrata in the lower intertidal zone; often forms distinct zonation patterns.

Description: Fucus serratus is a robust, olive-brown shrubby seaweed that frequently grows in high densities low on the shore, forming dense mats of long, ribbon-like fronds measuring up to 1 m in length and 2 to 5 cm in width. It anchors to rocks using a discoid holdfast approximately 3 cm in diameter. Although classified as a brown alga, its coloration ranges from olive green to reddish brown, often with a greenish tint.

Typically reaching lengths of up to 70 cm, F. serratus has been recorded at over 2 m in very sheltered environments. Its flat, strap-like fronds feature a forward-pointing serrated edge, a distinct midrib, and emerge from a short stipe. The fronds bifurcate repeatedly, splitting into two. Their surface is marked by numerous pinprick-like pores, each surrounded by clusters of tiny white hairs.

F. serratus resembles Fucus vesiculosus but lacks the prominent air bladders characteristic of that species. It is also similar to Fucus spiralis, though it does not exhibit the spirally twisted fronds typical of that species.

This seaweed thrives across a range of habitats, from exposed rocky shores to saline lagoons, but is most commonly found on sheltered, hard, rocky substrata in the lower parts of moderately sheltered coastlines. These areas are often subject to some degree of disturbance, such as tidal scour. Growth rates vary in environmental conditions, ranging from 4 to 12 cm per year. During winter storms, F. serratus plants may become detached and lost.

Figure 64. Fucus serratus. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen; (c) detail, reprinted from [17]; (d) Harvey’s illustration, reprinted from [18], public domain.

Fucus spiralis Linnaeus 1753 (Figure 65).

Order: Fucales; Family: Fucaceae.

Synonym: Fucus vesiculosus var. spiralis (Linnaeus) Roth 1800.

Common names: Flat wrack, Jelly bags, Spiral wrack, Spiraled Wrack.

Habitat: Marine species, attaches to rocky substrate on sheltered to moderately exposed shores.

Description: Well-developed plants are typically easy to recognize by their flattened, twisted, dichotomously branched thallus, which lacks air bladders. At the tips of the fronds, they bear large, oval receptacles, each surrounded by a narrow rim of vegetative tissue. However, younger specimens are not always easy to identify, and even mature individuals can be mistaken for Fucus ceranoides or bladderless forms of Fucus vesiculosus. Both of these species, however, possess narrower, more pointed receptacles that lack the surrounding vegetative rim.

Figure 65. Fucus spiralis. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

Fucus vesiculosus Linnaeus 1753 (Figure 66).

Order: Fucales; Family: Fucaceae.

Synonym: Virsodes vesiculosa (Linnaeus) Kuntze 1891.

Common name: Bladder Wrack.

Habitat: Found on rocks and stones in the mid-intertidal zone; often forms distinct zonation patterns.

Description: F. vesiculosus displays a wide range of colors, from olive green and olive brown to reddish brown and nearly black. It typically reaches about 40 cm in length, though its fronds can grow significantly longer. The species anchors itself securely to rocky surfaces using a small, disk-shaped holdfast.

One of its most distinctive features is the presence of small, nearly spherical gas-filled vesicles—resembling bubble wrap—that appear in pairs on either side of a prominent central midrib running along the strap-like frond. The flattened, branching fronds can grow between one and two meters in length. These air-filled bladders help the seaweed remain upright in its rocky habitat, enhancing its exposure to sunlight and maximizing its photosynthetic efficiency. F. vesiculosus tends to grow in dense clusters, forming extensive mats of long, ribbon-like fronds measuring up to 1 m in length and 5 cm in width. Its appearance fluctuates depending on environmental conditions—plants in sheltered regions develop numerous air bladders, whereas those in exposed areas have fewer or none. In smaller specimens, air bladders may be entirely absent. The absence of bladders is advantageous in turbulent environments, reducing the likelihood of severe damage and minimizing the risk of detachment and displacement.

Figure 66. Fucus vesiculosus. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Gongolaria baccata (S.G. Gmelin) Molinari & Guiry 2020 (Figure 67).

Order: Fucales; Family: Sargassaceae.

Synonym: Cystoseira baccata (S.G. Gmelin) P.C. Silva 1952.

Common names: Bushy berry wrack.

Habitat: Found on rocks, in large sandy intertidal pools, as well as in the lower intertidal and subtidal zones.

Description: This species features olive-brown fronds with a leathery consistency, which can exceed 1 m in length. The fronds are non-iridescent and turn black upon drying. Fixed by a thick and conical basal disk from which a slightly flattened and zig-zag-shaped main axis is located near the base (with about 1 × 0.4 cm in transverse section), which alternately branches out in a plane. Apices are smooth during periods of active growth and are surrounded by incurved young lateral branches. The lateral branch systems are distichous, alternate, radially symmetrical, and profusely branched in a repeatedly pinnate fashion. Branches of higher orders bear sparse, filiform appendages, which occasionally bifurcate.

Figure 67. Gongolaria baccata. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Gongolaria nodicaulis (Withering) Molinari & Guiry 2020 (Figure 68).

Order: Fucales; Family: Sargassaceae.

Synonym: Cystoseira nodicaulis (Withering) M. Roberts 1967.

Habitat: Found in large intertidal rock pools and lagoons, often with Ericaria selaginoides and Gongolaria baccata.

Description: The thallus, reaching up to 1 m in length, is typically solitary and secured by an irregular conical disk. Its cylindrical axis is commonly branched, featuring a smooth, rounded apex nestled between the bases or tophules of emerging laterals. The lateral branch systems, either radial or distichous, exhibit a striking greenish-blue iridescence when newly formed, extending to approximately 50 cm in length. These branches undergo repeated pinnate branching, either in a regular or irregular pattern, with sparse crypto-stomata and spine-like appendages. They are deciduous in summer, with early season laterals initially developing tophules, but later emerging without them.

Tophules are ovoid, measuring up to 15 mm in length, and may be smooth or covered in fine tubercles. They remain attached to the axis even after the lateral branches have been shed. Receptacles form at the terminal branchlets, appearing either simple or branched, with a nodose structure and typically bearing spine-like appendages. Air vesicles are subtle, presenting as dilations of the terminal branchlets—either solitary, arranged in series, or merged together. In some cases, they may be entirely absent.

Figure 68. Gongolaria nodicaulis, (a) underwater photo; (b) detail of terminal branches (reprinted with permission from Ignácio Bárbara); (c) detail of the fixing system, reprinted from [17].

Gongolaria usneoides (Linnaeus) Molinari & Guiry 2020 (Figure 69).

Order: Fucales; Family: Sargassaceae.

Synonym: Cystoseira usneoides (Linnaeus) M. Roberts 1968.

Common name: Bushy Bladder-Chain Wrack.

Habitat: Present in relatively deep rocky areas crossed by currents.

Description: The thallus is large and composed of a central axis with lateral branches bearing secondary branches. Those located closer to the base are flattened and exhibit a foliaceous appearance. Numerous vesicles are present throughout the structure.

Figure 69. Gongolaria usneoides; Scale on image (b): 1 division = 1 mm; (a) drift specimen; (b) herbarium specimen. Reprinted from [17].

Halidrys siliquosa (Linnaeus) Lyngbye 1819 (Figure 70).

Order: Fucales; Family: Sargassaceae.

Synonym: Cystoseira siliquosa (Linnaeus) C. Agardh 1820.

Common names: Pod-weed, Sea Oak.

Habitat: A distinctive and common rock pool seaweed found from the middle to lower shore. It may occasionally occur in the upper eulittoral, but only within rock pools. Additionally, it can form a zone in the sublittoral below the lower intertidal limit.

Description: This large, sturdy brown alga typically ranges from 0.3 to 1 m in length, though it can occasionally reach up to 2 m. It arises from a strong, flattened, cone-shaped holdfast. The main stem is flattened and branches alternately, giving the plant a distinctive zigzag appearance. Along the stem are a few flattened, ribbon-like leafy fronds.

Some branch tips bear characteristic pod-shaped air bladders, measuring approximately 0.5 cm in width and 1 to 4 cm in length. These bladders are divided by transverse septa into 10 to 12 compartments. The branches also carry reproductive bodies that resemble the bladders but lack internal septa.

Young specimens are olive-green in color, while older individuals become dark brown and leathery in texture.

Figure 70. Halidrys siliquosa; (a) underwater photo; (b) detail of terminal branches (all reprinted with permission from Ignácio Bárbara); (c) Harvey’s illustration, reprinted from [18], public domain.

Himanthalia elongata (Linnaeus) S.F. Gray 1821 (Figure 71).

Order: Fucales; Family: Himanthaliaceae.

Synonym: Fucus elongatus Linnaeus 1753.

Common names: Buttonweed, Sea Haricots, Sea Spaghetti, Sea thong, Thong Weed, Thongweed.

Habitat: Found in the lower eulittoral and sometimes extends into the shallow sublittoral.

Description: The thallus consists of a button-shaped vegetative structure measuring up to 30 mm in width and 25 mm in height. Emerging from this is a long, narrow, strap-like reproductive receptacle, light yellow-brown in color, reaching up to 2 m in length and up to 10 mm in width. Conceptacles are borne along this receptacle, which is sparingly branched.

Figure 71. Himanthalia elongata. Scale on image (c): 1 division = 1 mm; (a) button-shaped vegetative thallus; (b) long, narrow, strap-like, sparingly branched, light yellow-brown reproductive receptacle; (c) herbarium specimen, reprinted from [17]; (d) Harvey’s illustration, reprinted from [18], public domain.

Pelvetia canaliculata (Linnaeus) Decaisne & Thuret 1845 (Figure 72).

Order: Fucales; Family: Fucaceae.

Synonym: Ascophylla canaliculata (Linnaeus) Kuntze 1891.

Common names: Channel Wrack; Cow Tang.

Habitat: A distinctive and common rock pool seaweed found from the middle to lower shore. It may occasionally occur in the upper eulittoral, but only within rock pools. Additionally, it can form a zone in the sublittoral below the lower intertidal limit.

Description: This large, sturdy brown alga typically ranges from 0.3 to 1 m in length, though it can occasionally reach up to 2 m. It arises from a strong, flattened, cone-shaped holdfast. The main stem is flattened and branches alternately, giving the plant a distinctive zigzag appearance. Along the stem are a few flattened, ribbon-like leafy fronds.

Some branch tips bear characteristic pod-shaped air bladders, measuring approximately 0.5 cm in width and 1 to 4 cm in length. These bladders are divided by transverse septa into 10 to 12 compartments. The branches also carry reproductive bodies that resemble the bladders but lack internal septa.

Young specimens are olive-green in color, while older individuals become dark brown and leathery in texture.

Figure 72. Pelvetia canaliculata. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Sargassum muticum (Yendo) Fensholt (Figure 73).

Order: Fucales; Family: Sargassaceae.

Synonym: Sargassum kjellmanianum f. muticum.

Common name: Wireweed.

Habitat: Fixed in a great diversity of substrates, in rock pools at mid- and lower-intertidal and subtidal.

Description: This species is native to the Pacific region, particularly Japan, but has become well established along the coasts of Europe and North America. It is considered a nuisance by mariners due to its tendency to foul boat propellers and fishing nets, and its ability to disrupt the natural balance of indigenous marine flora and fauna. Its introduction to western North America and Europe was accidental, and it continues to expand its range in these regions, outcompeting native seaweed. In these areas, it is regarded as an invasive species.

The thallus is olive-brown and highly variable in size, capable of reaching several m in length. It is anchored to the substrate by a basal disk.

Figure 73. Sargassum muticum. Scale on images (b,c): 1 division = 1 mm; (a) underwater photo; (b) general view; (c) aerocysts or air vesicles. Reprinted from [17].

Scytosiphon lomentaria (Lyngbye) Link 1833 (Figure 74).

Order: Ectocarpales; Family: Scytosiphonaceae.

Synonym: Scytosiphon simplicissimus (Clemente) Cremades 1990.

Common names: Chipolata Weed, Leather tube.

Habitat: Typically found in the lower to mid-eulittoral zone, thriving on rocky surfaces along rough water to moderately sheltered coasts. The erect stage is seldom observed on seagrasses such as Zostera and Posidonia. S. lomentaria is frequently encountered on intertidal rocks during winter, often forming monospecific communities.

Description: Cylindrical thalli, ranging in color from yellowish-brown to dark brown, and can grow up to 400 mm in length. They are unbranched, with a width of 3–10 mm, tapering at both ends and anchored by a short stalk. Their hollow structure often features irregular constrictions.

Figure 74. Scytosiphon lomentaria. Scale on image (b): 1 division = 1 mm; (a) Field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

4.4. Big-Sized, Laminated Brown Macroalgae (Kelps)

Laminaria hyperborea (Gunnerus) Foslie 1885 (Figure 75).

Order: Laminariales; Family: Laminariaceae.

Synonym: Laminaria cloustonii Edmondston 1845.

Common names: Cuvie, Forest Kelp, May-weed, Northern Kelp, Sea rods.

Habitat: Found on bedrock or other stable substrata from extreme low water levels to depths determined by light penetration and sea urchin grazing—typically around 8 m in coastal waters, extending to 30 m in clearer coastal areas.

Description: This large and conspicuous kelp can grow up to 3.5 m in length under optimal conditions, although such size is rarely attained. Its broad, tough, and flat blade is divided into 5 to 20 digitate straps or fingers, with a glossy surface that ranges in color from golden brown to deep dark brown. The holdfast is substantial, conical, and branched, featuring prominent haptera that anchor the kelp securely to the substratum. The stipe is stiff and rough-textured, thick at the base, and gradually tapers toward the frond, maintaining an erect posture when exposed to air. Often encrusted with various epifauna and epiflora, the stipe’s growth and maximum length fluctuate based on seasonal changes, plant age, and environmental conditions.

Figure 75. Laminaria hyperborea. (a) field photo; (b) stipe and rhizoids detail, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Laminaria ochroleuca Bachelot Pylaie 1824 (Figure 76).

Order: Laminariales; Family: Laminariaceae.

Synonym: Laminaria iberica (Hamel) Lami 1934.

Common name: Golden Kelp.

Habitat: Predominantly found in intertidal zones of exposed sites, though it can occasionally occur at depths of up to 30 m, albeit less frequently.

Description: Glossy, yellow-brown kelp commonly found in intertidal zones. It stands out due to its ability to grow quite large under favorable conditions. While it can reach a maximum recorded length of 4 m, this is rarely attained and typically occurs only in specific regions. More commonly, it grows to approximately 2 m in length. The kelp features a substantial, heavy holdfast composed of thick haptera, up to 18 cm in diameter, which securely anchors it to rocky surfaces. From this base emerges a relatively long, rigid, round stipe that remains free of epiphytes and tapers slightly toward the blade. Notably strong and stiff, the stipe remains upright even when exposed to air. The blade is broad, flat, and leathery, divided into 5 to 20 strap-like digits. A distinctive yellow area at the junction between the stipe and blade serves as a key identifying feature. The entire plant displays a striking yellowish hue, highlighted by its smooth, bright, glossy texture. L. ochroleuca is a perennial kelp, retaining its stipe and holdfast throughout the year while regenerating a new blade annually.

Figure 76. Laminaria ochroleuca. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

Saccharina latissima (Linnaeus) C.E. Lane, C. Mayes, Druehl & G.W. Saunders 2006 (Figure 77).

Order: Laminariales; Family: Laminariaceae.

Synonym: Laminaria saccharina (Linnaeus) J.V. Lamouroux, 1813.

Common names: Kelp, Oarweed, Poor man’s Weather glass, Sea belt, Sugar sea belt, Sugar tang, Sugar wrack, Sugarwrack, Sweet tangle, Sweet wrack, tangle.

Habitat: Typically found from the sublittoral fringe down to depths of 30 m. It occasionally occurs in rock pools, though this is less common. The species generally thrives in sheltered marine environments.

Description: The sporophytes of S. latissima are a rich medium brown in color and feature a long, undivided frond that lacks a midrib. They possess a profusely branched holdfast and a stipe that can reach up to 50 cm in length. Mucilage ducts are absent from the stipe. The blade often displays two rows of bullations arranged longitudinally, parallel to the central axis. The frond is distinguished by its frilly, undulating margin.

Figure 77. Saccharina latissima. (a) adult sporophyte; (b) two sporophytes attached to a rock, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Saccorhiza polyschides (Lightfoot) Batters (Figure 78).

Order: Tilopteridales; Family: Phyllariaceae.

Synonym: Saccorhiza bulbosa.

Common names: Furbelows, Furbellows.

Habitat: On rocks, lower-intertidal and subtidal (to 35 m).

Description: Thallus leathery, brown, up to 2–4 m long. It is fixed by a distinctive large warty holdfast, a hollow bulb, crushed. The stipe is flattened, several cm wide, helical and with a wavy margin in the adult specimens, grows from the bulb, widening into a large flat blade deeply divided into numerous ribbon-like sections (usually dotted with tufts of filamentous epiphytic hairs and algae).

Figure 78. Saccorhiza polyschides (Lightfoot) Batters (Phaeophyceae); (a) field photo, * blade, ** bulb holdfast, *** flattened stipe; (b) bulb holdfast, hollow, large and warty, reprinted from [17].

Undaria pinnatifida (Harvey) Suringar (Figure 79).

Order: Laminariales; Family: Alariaceae.

Synonym: Alaria pinnatifida Harvey 1860.

Common names: Asian kelp, Apron-ribbon vegetable, Sea mustard, Precious sea grass, Wakame.

Habitat: Fixed to very varied substrates: rocks, blocks, ropes, remains of wood, etc., lower-intertidal and subtidal.

Description: This species is a non-native species in the seas of Europe (it is native to the NW Pacific). Thallus brown, somewhat translucent, reaching up to 3 m in length. It is fixed by means of a tangled set of thin and branching hapteron from which a stipe with an elliptical section with highly compressed edges starts (which in adult specimens carries coriaceous lateral expanses, spirally scalloped, giving it a corrugated appearance). The stipe is extended, as a midrib, through a whole blade, that is broad, flattened and lanceolate, membranous, deeply lobed in adults, which are frequently torn in the upper part (where it is reduced, sometimes, to the midrib).

Figure 79. Undaria pinnatifida. Scale on image (c): 1 division = 1 mm; (a) underwater photo; (b) field photo; (c) hapteron (*); stipe/midrib (**); blade (***). Reprinted from [17].

4.5. Bladder Like or Globose Algae

Colpomenia peregrina Sauvageau 1927 (Figure 80).

Order: Ectocarpales; Family: Scytosiphonaceae.

Synonyms: Colpomenia sinuosa var. peregrina Sauvageau 1927; Colpomenia peregrina (Sauvageau) Hamel 1937.

Common names: Oyster thief, Bladder weed.

Habitat: Generally growing epiphytically on other algae, and on mussels and oysters.

Description: Frond balloon-shaped when young, becoming contorted and collapsed with age, brown when young to yellowish-brown when older, usually 30–90 mm but up to 250 mm. Frond thin, like paper, delicate and full of seawater when young, hollow and empty when older.

Figure 80. Scale on image (c): 1 division = 1 mm; (a) Underwater photo; (b) detail; (c) herbarium specimen. Reprinted from [17].

Colpomenia sinuosa (Mertens ex Roth) Derbès & Solier 1851 (Figure 81).

Order: Ectocarpales; Family: Scytosiphonaceae.

Synonym: Asperococcus sinuosus (C. Agardh) Zanardini 1841.

Common name: Sinuous ballweed.

Habitat: Firmly attached to hard surfaces or epiphytic on other organisms, typically found from the lower intertidal zone down to depths of 15 m.

Description: The thallus is bladder-like—smooth, slick, hollow, and crisp—ranging in shape from spherical to sac-like. It may be irregularly expanded or somewhat lobed. Specimens typically reach up to 30 cm in diameter and 10 cm in height. The coloration is golden-brown, often covered with fine, colorless hairs. Reproductive sori appear as dark, raised patches on the surface.

Figure 81. Colpomenia sinuosa. Scale on image (b): 1 division = 1 mm; (a) Underwater photo; (b) detail; (c) drift specimen. Reprinted from [17].

Leathesia marina (Lyngbye) Decaisne 1842 (Figure 82).

Order: Ectocarpales; Family: Chordariaceae.

Synonym: Leathesia globosa Takamatsu 1939.

Common names: Punctured Ball Weed, Sea Cauliflower, Sea Potato, Brown Brains.

Habitat: Epilithic or epiphytic in the eulittoral zone.

Description: Yellow-brown, globose, and convoluted, with a slippery texture alga. They range in size from just a few cm to approximately 8 cm in diameter. Initially firm, they become hollow over time. The thallus primarily consists of a medulla composed of large cells that form a branched network. This species typically grows attached to rocks or as epiphytes on other seaweed.

Figure 82. Leathesia marina. (a) Field photo; (b) specimen detail, reprinted from [17].

5. Rhodophyta (Red Macroalgae)

5.1. Cylindrical Filamentous Red Macroalgae

Ahnfeltia plicata (Hudson) E.M. Fries 1836 (Figure 83).

Order: Ahnfeltiales; Family: Ahnfeltiaceae.

Synonym: Tylocarpus plicatus (Hudson) Kützing 1843.

Common names: Black Scour Weed, Bushy Ahnfelt’s Seaweed.

Habitat: A. plicata thrives in shallow sublittoral bedrock and rockpools along the lower shore, where it often finds itself partially buried in sand. It can also contribute to turf formation on soft or friable rocks that lack the stability needed for larger fucoid species. While the tetrasporophyte phase is frequently found growing on pebbles, mature gametophytes are restricted to more stable substrates.

Description: A perennial red seaweed that forms dense, tangled tufts. The fronds are very fine, tough, and wiry, with irregular or dichotomous branching, and can reach lengths of up to 21 cm. The holdfast is disk-like or encrusting, typically measuring between 0.5 and 2 cm in diameter. When it is moist, the fronds are dark brown, appearing nearly black when dry. The uppermost branches often exhibit a greenish hue.

Figure 83. Ahnfeltia plicata. Scale on image (b): 1 division = 1 mm; (a) underwater photo, reprinted with permission from Ignácio Bárbara; (b) herbarium specimen. Reprinted from [17].

Antithamnion densum (Suhr) M. Howe 1914 (Figure 84).

Order: Cermiales; Family: Ceramiaceae.

Synonym: Callithamnion densum Suhr 1840.

Habitat: Infralittoral rock and other hard substrata.

Description: Recognized for its compact, dense growth, the species name “densum” reflects this trait, derived from the Latin word meaning “dense”.

Figure 84. Antithamnion densum. Microscopic observation: (a) 40×; (b) 100×. Reprinted from [17].

Asparagopsis armata Harvey 1855 (Figure 85).

Order: Bonnemaisoniales; Family: Bonnemaisoniaceae.

Synonym: Falkenbergia rufolanosa (Harvey) F. Schmitz 1897.

Common name: Harpoon weed.

Habitat: Both life cycle phases reproduce readily through vegetative means. Drift specimens of the gametophyte can easily attach to other algae using barbed branchlets, subsequently producing new shoots. This species was introduced from the Southern Hemisphere.

Description: In northeastern Europe, gametophyte plants emerge between June or July and August or September, sometimes persisting through winter. They exhibit a pale purplish-red coloration but quickly degrade when removed from water, turning a distinct orange. The fronds are bushy, with a cylindrical axis up to 1 mm wide and 200 mm long, originating from bare, creeping stolons. Branching is irregular, consisting of four rows of branchlets—short, simple ones alternating with longer branchlets that bear four rows of fine, filamentous ramuli. The lower branchlets remain unbranched, tapering to a point and adorned with harpoon-like barbs.

The tetrasporophyte phase, known as the “Falkenbergia phase,” is present year-round, with peak visibility between October and March. It appears brownish-red, extensively branched, and filamentous, forming dense, cotton-wool-like tufts up to 15 mm in diameter.

Figure 85. Asparagopsis armata. Scale on image (b): 1 division = 1 mm; (a) gametophyte phase underwater photo; (b) herbarium specimen; (c) Falkenbergia rufolanosa-phase; underwater photo. Reprinted from [17].

Asparagopsis taxiformis (Delile) Trevisan 1845 (Figure 86).

Order: Bonnemaisoniales; Family: Bonnemaisoniaceae.

Synonym: Falkenbergia hillebrandii (Bornet) Falkenberg 1901.

Common name: Supreme Limu.

Habitat: A tropical to subtropical species, with thalli that are epilithic. It typically inhabits shallow subtidal zones characterized by strong water movement.

Description: The thallus forms delicate, filamentous mats or tufts, reaching up to 4 cm in height, with a bright light pink coloration. Branching is irregular to alternate, with cylindrical branches that are sometimes moniliform, featuring bead-like swollen segments measuring 30–80 µm in diameter. The central axial filament is surrounded by three pericentral cells, which typically taper to pointed tips and are approximately twice as long as they are wide. Each set is rotated about 60°. At the apex, a single prominent apical cell gives rise to a lens-shaped basal cell. The holdfast begins as a disk-like structure, later evolving into a branched, tangled, creeping mass of filaments. In the “Falkenbergia-phase” (tetrasporophyte), tetrasporangia appear singly on the outer filaments, rather than in clusters or series, and originate from one pericentral cell of each segment. The color ranges from red to bluish violet. With its fluffy texture and “Christmas tree”-like shape, the thallus grows between 3 and 15 cm high.

Figure 86. Asparagopsis taxiformis. (a,b) underwater photos, reprinted from [17]; (c) Hervey’s illustration, reprinted from [18], public domain.

Bonnemaisonia asparagoides (Woodward) C. Agardh 1822 (Figure 87).

Order: Bonnemaisoniales; Family: Bonnemaisoniaceae.

Synonym: Plocamium asparagoides (Woodward) J.V. Lamouroux 1813.

Habitat: Commonly found on rocky substrates in the very low intertidal zone and subtidal areas down to 30 m. It is widely distributed and frequently encountered. The sporophyte phase is restricted to subtidal habitats, typically occurring on shells, stones, and other hard surfaces, but is considered very rare.

Description: The gametophyte features feathery, highly branched fronds that can extend up to 250 mm in length. Its main axis is cylindrical or slightly compressed, reaching up to 3 mm in width and originating from a small discoid base. The branches alternate in a distichous arrangement and are adorned with alternating, spinelike corticated ramuli, each approximately 2 mm in length, all positioned within a single plane. The tetrasporophyte, in its Hymenoclonium phase, appears as a minute, prostrate disk measuring between 2 and 4 mm in diameter.

Figure 87. Bonnemaisonia asparagoides. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen; (b) microscopic observation (40×). Reprinted from [17].

Bostrychia scorpioides (Hudson) Montagne 1842 (Figure 88).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Helicothamnion scorpioides (Roth) Kützing 1843.

Habitat: Found on muddy shores near the high-water mark, typically growing on the lower stems of saltmarsh flowering plants. It is widely distributed and locally abundant.

Description: The frond is flexuous, dull purple, and filiform—much branched, inarticulate, and dotted. Branching is sub-dichotomous, with branches three to four times pinnate. Both pinnae and pinnula are patent, and the apices are strongly rolled inward.

Figure 88. Bostrychia scorpioides. (a) microscopic observation (100×), reprinted from [17]; (b) Hervey’s illustration, reprinted from [18], public domain.

Callithamnion corymbosum (Smith) Lyngbye 1819 (Figure 89).

Order: Ceramiales; Family: Callithamniaceae.

Synonym: Conferva corymbosa Smith 1812.

Habitat: A marine and estuarine species typically found in rock pools and on sandy rocks, especially in areas with widely fluctuating salinity levels, such as the upper shore.

Description: Brownish-red fronds reaching up to 50 mm in length. Filaments are uniseriate and corticated at the base, exhibiting repeated branching with simple, alternate branches. The ultimate branchlets are densely covered in tufts of alternate ramuli, forming a corymbose structure. These branchlets curve inward and taper at both the base and the tip. The articulations of the main axes are 2 to 4 times longer than they are wide, while those of the ramuli are approximately 1.5 times as long as they are broad.

Figure 89. Callithamnion corymbosum, microscopic observations: (a) gonimocarps (40×); (b) gonimocarp (100×). Reprinted from [17].

Callithamnion granulatum (Ducluzeau) C. Agardh 1828 (Figure 90).

Order: Ceramiales; Family: Callithamniaceae.

Synonym: Ceramium granulatum Ducluzeau 1805.

Habitat: Typically, epiphytic on Corallina officinalis and also found on mussels in the lower intertidal zone of exposed coasts. It is widely distributed, though more commonly observed along the southern and western coasts.

Description: Tufted fronds ranging in color from purplish to bleached yellow. Filaments are uniseriate and corticated at the base, reaching up to 150 mm in length. The main axis is extensively and irregularly branched, with all branches densely covered in short, repeatedly dichotomous ramuli featuring wide axils. Articulations are two to three times as long as they are broad.

Figure 90. Callithamnion granulatum. (a) underwater photo; (b) microscopic observation of tetrasporangia (40×) (all reprinted with permission from Ignácio Bárbara).

Callithamnion tetragonum (Stackhouse) S.F. Gray 1821 (Figure 91).

Order: Ceramiales; Family: Callithamniaceae.

Synonym: Conferva tetragona Stackhouse 1796.

Habitat: Epiphytic, lower intertidal and subtidal, widely distributed, frequent.

Description: The fronds exhibit a brownish-red hue and can grow up to 50 mm in length. The filaments are uniseriate and corticated at the base, displaying a repetitive branching pattern with simple, alternating branches. The ultimate branchlets are densely covered with tufts of alternate ramuli, forming a corymbose structure that curves inward and tapers at both the base and apex. The main axes have articulations that are two to four times longer than they are wide, while those of the ramuli are approximately 1.5 times longer than their width.

Figure 91. Callithamnion tetragonum. Scale on image (b): 1 division = 1 mm; (a) field photo (reprinted with permission from Ignácio Bárbara); (b) herbarium specimen, reprinted from [17]; (c) general view (reprinted with permission from Ignácio Bárbara).

Callithamnion tetricum (Dillwyn) S.F. Gray 1821 (Figure 92).

Order: Ceramiales; Family: Callithamniaceae.

Synonym: Conferva tetrica Dillwyn 1806.

Habitat: A marine species commonly found on shady rocks beneath fucoid canopies in the lower intertidal and subtidal zones. It is prevalent along the southern and western coasts.

Description: Forms shaggy, rigid tufts of dark brownish-red coloration, reaching up to 200 mm in length and arising from a large discoid base. The main axes and branches are corticated and often interwoven with adventitious laterals. Branches are irregularly alternate, with final-order branches bearing alternate pinnate ramuli. These ramuli are somewhat attenuate at both base and apex, with cells measuring approximately 1 to 1.5 times as long as they are broad.

Figure 92. Callithamnion tetricum. microscopic observations: (a) (10×) and (b) (10×) (reprinted with permission from Ignácio Bárbara); (c) herbarium specimen (scale: 1 division = 1 mm), reprinted from [17].

Carradoriella denudata (Dillwyn) Savoie & G.W. Saunders 2018 (Figure 93).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Polysiphonia denudata (Dillwyn) Greville ex Harvey 1833.

Common name: Wide-branched Siphon Weed.

Habitat: Primarily grows on shells and stones within soft-sediment habitats.

Description: The thallus consists of small, reddish-brown fronds with cylindrical, uncrossed axes that branch in a dichotomous pattern. These primary structures give rise to secondary branches, which bear cystocarps.

Figure 93. Carradoriella denudata. Microscopic observations: (a) general view (5×); (b) cystocarp (10×); (c) cross section (40×) (all reprinted with permission from Ignácio Bárbara).

Carradoriella elongata (Hudson) Savoie & G.W. Saunders 2018 (Figure 94).

Order: Ceramiales; Family: Ceramiaceae.

Synonym: Polysiphonia elongata (Hudson) Sprengel 1827.

Habitat: A marine species found on stones and shells in open sandy and gravelly substrates, ranging from the intertidal zone to deeper subtidal areas. It is widely distributed and commonly and is sometimes washed ashore in large quantities.

Description: The fronds are cartilaginous, cylindrical, and dark reddish-brown, reaching up to 300 mm in length. Crimson ramuli emerges from a discoid base. Branching occurs in an alternating to pseudo-dichotomous pattern, with dense, gelatinous, ephemeral ramuli appearing in spring. These taper at both the base and apex.

The internal structure includes a small central siphon, surrounded by four large primary pericentral siphons and four alternating secondary pericentral siphons. In older regions, eight tertiary pericentral siphons are present, encased by a layer of corticating cells. Articulations are faintly visible in corticated sections—broader than long near the base, transitioning to longer than broad in the ramuli.

Figure 94. Carradoriella elongata. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen; (b) microscopic observation (10×); (c) transversal section (40×) (all reprinted with permission from Ignácio Bárbara).

Ceramium echionotum J. Agardh 1844 (Figure 95).

Order: Ceramiales; Family: Ceramiaceae.

Synonym: Chaetoceras echionotum (J. Agardh) Kützing 1847.

Habitat: Marine species, on rocks and stones and epiphytic.

Description: Rough, densely tufted fronds in a purplish-red hue, reaching up to 150 mm in length. Its structure is repeatedly dichotomously branched, with wide axils and strongly hooked inward apices. The filaments maintain a nearly uniform diameter throughout, while the articulations are corticated at the nodes—being 3 to 4 times as long as broad in the lower parts and very short distally. Additionally, numerous irregularly distributed, colorless, unicellular, needle-like spines adorn the corticating bands.

Figure 95. Ceramium echionotum. Scale on image (a): 5 cm; (a) general view, reprinted from [28], public domain; (b) microscopic observation of bifurcated apices and corticating transverse bands with emerging unicellular spines (100×) (reprinted with permission from Ignácio Bárbara).

Ceramium secundatum Lyngbye 1819 (Figure 96).

Order: Ceramiales; Family: Ceramiaceae.

Synonym: Ceramium rubrum subsp. secundatum (Lyngbye) J. Agardh 1851.

Habitat: This species primarily grows as an epiphyte on larger red algae like Gracilaria spp. and Carradoriella elongata, though it is occasionally found on smaller perennial algae and Laminaria hyperborea fronds. It is commonly observed in submerged environments, attaching to artificial surfaces such as marina pontoons and mooring buoys. Its presence ranges from occasional to frequent in deep sandy lower-shore pools, with substantial populations thriving at depths of 1 to at least 11 m in sandy habitats, including Zostera marina.

Description: This species features an erect axis with numerous branches, distinguished by darker cortical bands marking the boundaries of its cell walls. The branches terminate in curved, paired apices (tips) and can reach a height of 50–150 mm.

Figure 96. Ceramium secundatum. (a) general view; (b) microscopic observation (40×) (reprinted with permission from Ignácio Bárbara).

Ceramium tenuicorne (Kützing) Wærn 1952 (Figure 97).

Order: Ceramiales; Family: Ceramiaceae.

Synonym: Ceramium corticatulum Kylin 1907.

Habitat: Found in a variety of marine and brackish water habitats, especially in coastal areas influenced by tides and freshwater runoff.

Description: This species features a uniaxial, cylindrical, and erect thallus with a dark red coloration. Its branch apices are bifurcated and curved, while the filaments consist of transverse bands of low, thick cortical cells (nodes), interspersed with smaller nodes.

Figure 97. Ceramium tenuicorne. (a) general view; (b) microscopic observation (60×) (all reprinted with permission from Ignácio Bárbara).

Ceramium virgatum Roth 1797 (Figure 98).

Order: Ceramiales; Family: Ceramiaceae.

Synonym: Conferva polymorpha Linnaeus 1753.

Habitat: C. virgatum is both epilithic and epiphytic, commonly found growing on the stipes and fronds of Fucus spp., Mastocarpus stellatus, and Laminaria hyperborea, as well as on the leaves of Zostera marina.

Description: This small red seaweed can reach up to 30 cm in height. It has filamentous fronds with irregular, dichotomous branching, and the branches gradually taper into characteristic pincer-like tips. The holdfast is a tiny conical disk, from which a dense network of rhizoidal filaments extends. The plant displays a reddish-brown to purple coloration and, under close examination, reveals a distinct banded pattern.

Figure 98. Ceramium virgatum. (a) general view (reprinted with permission from Ignácio Bárbara); (b) herbarium specimen (1 division = 1 mm); microscopic observation (40×), reprinted from [17].

Compsothamnion thuioides (Smith) F. Schmitz 1889 (Figure 99).

Order: Ceramiales; Family: Wrangeliaceae.

Synonym: Conferva thuioides Smith 1810.

Habitat: Found in marine environments, specifically on exposed, lower infralittoral rock. It prefers areas with full salinity (30–35 ppt), rocky substratum (bedrock and large boulders), and depths ranging from 5–10 m to 20–30 m.

Description: Uniseriate thallus, erect and with alternate ramifications. The lateral branches are, in turn, branched alternately giving rise to branches of higher order which are also branched.

Figure 99. Compsothamnion thuioides. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen; (b) microscopic observation (10×), reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Crouania attenuata (C. Agardh) J. Agardh 1842 (Figure 100).

Order: Ceramiales; Family: Callithamniaceae.

Synonym: Mesogloia attenuata C. Agardh 1824.

Habitat: Marine zones; brackish and freshwater bodies.

Description: Small, compact tufts of reddish-pink coloration. The tufts consist of protruding main axes that branch irregularly and alternately, producing lateral branches. These lateral branches are composed of quadrate cells and are covered with curved, mucronate ramuli that are vertically displaced.

Figure 100. Crouania attenuata. (a) microscopic observation (10×); (b) microscopic observation (40×): tufts are formed by the projection of the main axes branching irregularly and giving alternating lateral branches. Reprinted from [17].

Dasya hutchinsiae Harvey 1833 (Figure 101).

Order: Ceramiales; Family: Delesseriaceae.

Habitat: On rocks or epiphytic, shady low intertidal pools and subtidal, southern and western coasts to Orkney Islands, occasionally.

Description: The fronds are crisp and bushy, displaying striking crimson to brownish-red coloration, reaching up to 100 mm in length. The numerous, irregular branches are densely covered with stiff, patent, repeatedly dichotomous mono-siphonous ramuli. The ramuli measure up to 20 μm in diameter, featuring blunt apices, with cells that are three to four times longer than they are wide. The main axis consists of a central siphon surrounded by five pericentral siphons and is fully corticated.

Figure 101. Dasya hutchinsiae. (a) underwater photo, reprinted from [17]; (b) microscopic observation (10×). Reprinted from [17].

Dasysiphonia sessilis (Yamada) M.M. Cassidy, C.W. Schneider & G.W. Saunders 2022 (Figure 102).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Dasya sessilis Yamada 1928.

Habitat: Marine and transitional waters species.

Description: D. sessilis is a red alga native to the Northwest Pacific, ranging from the Philippines to Russia. It has been introduced to several regions, including the Netherlands, Spain, Portugal, Mediterranean France, and southern California.

This species exhibits an alternation of generations, consisting of asexual tetrasporophytic plants and sexual gametophytic plants.

These plants anchor to a holdfast and develop multiple erect stems, ranging from 50 to 250 mm in height for tetrasporophytic specimens and 60 to 130 mm for gametophytic specimens. They produce numerous branches that extend into finer branchlets, densely covered with hair-like structures. Their coloration varies from a deep rose-red to an intense, almost fluorescent pink.

Figure 102. Dasysiphonia sessilis. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) general view, reprinted from [17]; (c) microscopic observation: female thalli with cystocarp (40×); (d) microscopic observation: spermatangial heads (20×) (reprinted with permission from Ignácio Bárbara).

Gaillona rosea (Roth) Athanasiadis 2016 (Figure 103).

Order: Ceramiales; Family: Callithamniaceae.

Synonym: Aglaothamnion roseum (Roth) Maggs & L’Hardy-Halos 1993.

Common name: Rosendun.

Habitat: It thrives as an epiphyte, epizoic, and epilithic organism, spanning habitats from the low littoral zone to depths of 20 m in the sublittoral.

Description: The thallus is filamentous, upright, and delicately branched, reaching up to 7 cm in length, with corticating rhizoidal filaments concentrated near the base of the main axis.

Figure 103. Gaillona rosea. Reproductive thalli: (a) microscopic observation (20×); (b) microscopic observation (40×) (all reprinted with permission from Ignácio Bárbara).

Gaillona seposita (Gunnerus) Athanasiadis 2016 (Figure 104).

Order: Ceramiales; Family: Callithamniaceae.

Synonym: Aglaothamnion sepositum (Gunnerus) Maggs & Hommersand 1993.

Common name: Beautiful Bush Weed.

Habitat: It flourishes as an epiphytic, epizoic, and epilithic species, inhabiting environments from the low littoral zone down to 20 m in the sublittoral.

Description: Dense tufts of uniseriate filaments, dark brown-red in color, reaching up to 200 mm in height. The thallus is opaque, cartilaginous, and heavily corticated by rhizoidal filaments. It displays repeated branching, with branches enveloped by pinnate ramuli. The cells of the ramuli are elongated, approximately twice as long as they are wide.

Griffithsia corallinoides (Linnaeus) Trevisan 1845 (Figure 105).

Order: Ceramiales; Family: Wrangeliaceae.

Figure 104. Gaillona seposita. (a) general view; reproductive thalli: (b) microscopic observation (20×); (c) microscopic observation (40×) (all reprinted with permission from Ignácio Bárbara).

Synonym: Callithamnion corallinoides (Linnaeus) Lyngbye 1819.

Common name: Mrs Griffiths’s Coral Weed.

Habitat: Marine species, on rocks, stones and shells, lower intertidal pools and subtidal, in sheltered waters, occasional to frequent, widely distributed. Most obvious in spring and early summer.

Description: This species features gelatinous, tufted, uniseriate, and ecorticate crimson filaments, reaching up to 200 mm in length. Its branching is repeatedly dichotomous, with wide axils. The articulations in the lower sections are club-shaped, measuring four to five times their width, while the distal segments are short and bead-like. It is also noted for its strong odor.

Figure 105. Griffithsia corallinoides. Scale on image (a): 1 division = 1 mm; (a) general view, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Halurus equisetifolius (Lightfoot) Kützing (Figure 106).

Order: Ceramiales; Family: Wrangeliaceae.

Synonym: Griffithsia equisetifolia (Lightfoot) C. Agardh 1817.

Common names: Sea tail, Sea horsetail.

Habitat: On rocks and epiphytic, low-intertidal pools and shallow subtidal.

Description: Dark red thallus, of spongy consistency when out of water, up to 22.5 cm. It is fixed to the substrate by a basal disk, from which a cylindrical axis begins, which ramifies irregularly several times. Axes and branches are densely covered by verticils of 5 to 8 short branches, arranged in spirals at regular intervals, incurved, all of the same size and branched out di-trichotomically.

Figure 106. Halurus equisetifolius. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) general view; (c) axes covered by verticils of short branches (40×). Reprinted from [17].

Halurus flosculosus (J. Ellis) Maggs & Hommersand 1993 (Figure 107).

Order: Ceramiales; Family: Wrangeliaceae.

Synonym: Griffithsia flosculosa (J. Ellis) Batters 1902.

Common name: Mrs Griffiths’s Little Flower.

Habitat: Marine species, on rocks in shady intertidal pools.

Description: Stiff and tufted, with uniseriate, ecoritcate filaments that exhibit a vivid red hue, reaching lengths of up to 200 mm. The branching pattern is predominantly dichotomous, with frequent short branchlets and sharply acute axils. Articulations are cylindrical, measuring 5–6 times their width in the lower regions, gradually becoming shorter towards the distal ends.

Figure 107. Halurus flosculosus. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) specimen detail (all reprinted with permission from Ignácio Bárbara).

Helminthocladia calvadosii (J.V. Lamouroux ex Duby) Setchell 1915 (Figure 108).

Order: Nemaliales; Family: Liagoraceae.

Synonym: Dumontia calvadosii J.V. Lamouroux ex Duby 1830.

Habitat: Inhabits sheltered, silty areas on rocks within the intertidal or shallow subtidal zones.

Description: These erect plants originate from a single discoid holdfast and can reach up to 60 cm in height. Their coloration ranges from red to brown, with a mucilaginous, smooth, and slippery yet firm texture. Branching varies from radial to irregular, while the main axes are either terete or slightly compressed, measuring 2–15 mm in diameter at the base and narrowing to 0.4–2 mm at the top. Lateral and adventitious branches differ in abundance, from sparse to numerous; they are elongated, either simple or subtly branched, tapering progressively from apex to base.

Figure 108. Helminthocladia calvadosii. (a) underwater photo, reprinted from [17]; (b) general view (reprinted with permission from Ignácio Bárbara); (c) Harvey’s illustration, reprinted from [18], public domain.

Heterosiphonia plumosa (J. Ellis) Batters 1902 (Figure 109).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Conferva plumosa J. Ellis 1768.

Common name: Siphoned Feather Weed.

Habitat: Found on rocks and as an epiphyte, this species thrives in low intertidal pools and subtidal zones along southern and western shores. It is abundant in the south but becomes increasingly rare in northern regions.

Description: This seaweed ranges in color from red to deep crimson, appearing black when dried. It has a flattened, fern-like structure with a hairy thallus emerging from a discoid holdfast. The fronds, either flat or slightly cylindrical, grow up to 20 cm in length and 0.5 cm in diameter at the base, gradually narrowing towards the apex. The main frond branches in a single plane with alternate but irregular spacing of up to 1 cm between each branch. The branches are bare at the base, while the upper portions feature a scattered, alternating arrangement of secondary branches. These secondary branches decrease in length towards the apex, each adorned with numerous pointed branchlets, creating a tufted, feather-like appearance.

Figure 109. Heterosiphonia plumosa. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Leptosiphonia brodiei (Dillwyn) Savoie & G.W. Saunders 2018 (Figure 110).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Polysiphonia brodiei (Dillwyn) Sprengel 1827.

Common name: Brodie’s Siphon Weed.

Habitat: Marine species, on rocks, stones, shells and corallines, mid-intertidal pools to subtidal, especially on exposed shores, generally distributed, common.

Description: The fronds are cartilaginous, cylindrical, and tufted, displaying a deep purple-red hue and reaching up to 300 mm in length, originating from a small, conical basal disk. The branching pattern is irregular to pseudo-dichotomous, densely covered with short, slender, and intricately divided branchlets, creating the distinct tufted appearance characteristic of this species. The central siphon of the main axes features 6–8 primary pericentral siphons, interspersed with alternating secondary pericentral siphons, all enveloped by small corticating cells. The branchlets remain ecorticate, possessing fewer pericentral siphons, with articulations that are approximately as long as they are broad.

Figure 110. Leptosiphonia brodiei. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from [17]; (b) tetrasporangial thalli microscope observation (100×) (reprinted with permission from Ignácio Bárbara); (c) Harvey’s illustration, reprinted from [18], public domain.

Liagora viscida (Forsskål) C. Agardh 1822 (Figure 111).

Order: Nemaliales; Family: Liagoraceae.

Synonym: Sphaerococcus viscidus (Forsskål) C. Agardh 1817.

Habitat: On firm substrata in shallow water to 5 m depht.

Description: The thallus is tufted, exhibiting colors ranging from gray-purple to greenish-white or pink. It features repeated dense branches of nearly uniform length, with terete branches that gradually taper towards the top. The terminal branches typically spread as wide-angled bifurcations. Moderately calcified, it has a flexible yet firm texture.

Melanothamnus harveyi (Bailey) Díaz-Tapia & Maggs 2017 (Figure 112).

Order: Ceramiales; Family: Rhodomelaceae.

Figure 111. Liagora viscida. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

Synonym: Polysiphonia harveyi Bailey 1848.

Common name: Harvey’s Siphon Weed.

Habitat: Grows epiphytically on other algae as well as on artificial material.

Description: This species forms compact tufts that reach a maximum height of 10 cm. Its upright branches originate from a central axis encircled by four equally sized pericentral cells. A cortex may develop as cells extend downward into the grooves between pericentrals. Lateral branches tend to be dense, contributing to their overall structure. The holdfast consists of a disk-like arrangement of descending filaments, from which new erect branches continue to emerge. Its general appearance varies significantly.

Figure 112. Melanothamnus harveyi. (a) general view; (b) ramifications detail; (c) microscopic observation of the thallus cross section (100×) (all reprinted with permission from Ignácio Bárbara).

Pleonosporium borreri (Smith) Nägeli 1862 (Figure 113).

Order: Ceramiales; Family: Wrangeliaceae.

Synonym: Callithamnion borreri (Smith) C. Agardh 1828.

Common name: Borrer’s Seed Weed

Habitat: This species is epiphytic, epizoic, or epilithic, occurring in the low littoral zone and extending to depths of up to 30 m.

Description: This species has an erect, filamentous thallus with alternate branching. Its lateral branches also divide alternately, leading to the development of the cystocarps, which is composed of small quadratic cells with rounded apices.

Figure 113. Pleonosporium borreri. (a) microscopic observation (100×) (reprinted with permission from Ignácio Bárbara); (b) Harvey’s illustration, reprinted from [18], public domain.

Pleonosporium flexuosum (C. Agardh) Bornet 1892 (Figure 114).

Order: Ceramiales; Family: Wrangeliaceae.

Synonym: Callithamnion flexuosum (C. Agardh) C. Agardh 1828.

Common name: Flexuous bog-moss.

Habitat: Typically grows in slightly mineral-rich habitats like poor fens and wet woodlands. It prefers conditions that are not the most acidic.

Description: Marine alga characterized by its distinctive zigzag-shaped thallus, a feature that inspired its name, derived from the Latin word meaning “zigzag”.

Figure 114. Pleonosporium flexuosum. Microscopic observations: (a) 10×; (b) 20×; (c) 40× (all reprinted with permission from Ignácio Bárbara).

Plumaria plumosa (Hudson) Kuntze 1891 (Figure 115).

Order: Ceramiales; Family: Wrangeliaceae.

Synonym: Plumaria elegans (Bonnemaison) F. Schmitz 1889.

Common name: Soft Feather Weed.

Habitat: Grows on shaded areas of the lower littoral rocky shore, particularly on vertical rocks and overhangs.

Description: This species has soft, tufted fronds that range from dark blackish to brownish red. The fronds are mono-siphonous, corticate at the base, and ecorticate toward the top, reaching lengths of up to 100 mm. They exhibit repeated pinnate branching, which can be either dichotomous or alternate, with opposite ramuli. The ultimate ramuli are densely arranged, blunt, slightly curved, and longer on the outer side than on the inner side.

Figure 115. Plumaria plumosa. (a) Herbarium specimen (reprinted from Wikimedia [29], public domain); (b) Harvey’s illustration, reprinted from [18], public domain.

Pterothamnion plumula (J. Ellis) Nägeli 1855 (Figure 116).

Order: Ceramiales; Family: Ceramiaceae.

Synonym: Antithamnion plumula (J. Ellis) Thuret 1863.

Common name: Bushy Feather Weed.

Habitat: Marine species, down to about 30 m depth on rocky bottoms and on other algae.

Description: This species features multiple paired branches adorned with upright tufts reaching up to 15 cm in height. Cotton-like pink clusters, which are short-lived and appear during the summer months. As annual algae, they grow and proliferate swiftly, competing aggressively with perennial species for both space and light.

Figure 116. Pterothamnion plumula. Scale on image (a): 1 division = 1 mm; (a) general view; (b) microscopic observation (40×) (all reprinted with permission from Ignácio Bárbara).

Rhodochorton purpureum (Lightfoot) Rosenvinge 1900 (Figure 117).

Order: Acrochaetiales; Family: Rhodochortonaceae.

Synonym: Audouinella purpurea (Lightfoot) Woelkerling 1973.

Common name: Rödplysch.

Habitat: Found on rocks or growing epiphytically, particularly on Laminaria hyperborea stipes, this species thrives from the upper infralittoral zone to the subtidal region. It is frequently encountered in caves and shaded crevices, displaying a wide distribution and common presence.

Description: These plants develop into matted purplish-red tufts or a delicate turf of sparsely branched, upright filaments, ranging from 5 to 10 mm in length. Their cells are three to four times longer than they are wide and contain a single reticulate plastid without pyrenoids, which later fragments. Reproduction occurs primarily in winter through tetrasporangia, while monosporangia are absent.

Figure 117. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from [17]; (b) microscopic observation (40×) (reprinted with permission from Ignácio Bárbara).

Rhodothamniella floridula (Dillwyn) Feldmann (Figure 118).

Order: Palmariales; Family: Rhodothamniellaceae.

Synonym: Audouinella floridula (Dillwyn) Woelkerling 1971.

Common name: Sand binder.

Habitat: Turf-forming on sand-covered rocks, from the upper intertidal to the upper subtidal.

Description: Forming a dense, brownish-red or purplish-red turf of sparingly branched erect and uniseriate filaments. The filaments bind with sand at the base, forming a spongy carpet like mass that appears as tufts of hair when uncovered by the ebbing tide (having a purplish tinge when dry). The filaments are well-spaced and branch out up to 3 cm in length. Cells oblong, 3–4 times longer than broad. Several plastids, each with a pyrenoid, against cell wall. Tetrasporangia ovoid, arranged on the upper parts of the erect axes, occurring singly or in clusters and mostly in winter.

Figure 118. Rhodothamniella floridula (Dillwyn) Feldmann (Rhodophyta). Scale on image (a): 1 division = 1 mm; (a) general view; (b) tetrasporangia on the upper parts of the axes (40×) (all reprinted with permission from Ignácio Bárbara).

Vertebrata fucoides (Hudson) Kuntze (Figure 119).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Polysiphonia fucoides (Hudson) Greville 1824.

Common names: Black siphon weed.

Habitat: On hard substrate or epiphyte at the intertidal zone.

Description: Brownish purple, rich tufted branching from the base, 7–30 cm high; flaccid, slippery, cylindrical. Lateral axes of higher order increasingly thinner and shorter, branching alternate, tripinnate, ramuli with terminal tufts of colorless dichotomous fibrils (trichoblasts). With 9–20 pericentral cells, corticated only at base, articulations as long as broad in older parts, to 1.5 times as long as broad distally.

Figure 119. Vertebrata fucoides (Hudson) Kuntze (Rhodophyta). Scale on images (b,c): 1 division = 1 mm; (a) field photo; (b) general view; (c) detail; (d) trichoblast (100×); (e) cross section 100×); (f) tetrasporophyte (100×); (g) cystocarps (100×) (all reprinted with permission from Ignácio Bárbara).

Vertebrata thuyoides (Harvey) Kuntze (Figure 120).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Boergeseniella thuyoides (Harvey) Kylin 1956.

Common name: Tufted conifer weed.

Habitat: Found on rock and as an epiphyte in shallow pools within the lower intertidal zone.

Description: The plant features tufted fronds of deep brownish-purple coloration, cartilaginous and cylindrical in form, reaching up to 150 mm in height. These fronds arise from a creeping rhizoidal base. Branching is distichously bi- to tripinnate, with short, patent branches of nearly uniform length, creating a linear appearance. Ramuli are short and spine-like.

Figure 120. Vertebrata thuyoides. (a) underwater photo; (b) thallus apices (40×); (c) cross section (100×) reprinted from [17].

Internally, the central siphon is surrounded by 8–12 pericentral siphons, and the outer cortication consists of small, pigmented cells.

Vertebrata fruticulosa (Wulfen) Kuntze (Figure 121).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Boergeseniella fruticulosa (Wulfen) Kylin 1956.

Common name: Tufted Shrub Weed.

Habitat: Found on rocks and as an epiphyte in shallow pools within the lower intertidal zone.

Description: A small, branched red alga reaching up to 15 cm in length. The erect axes are encircled by 11 to 12 pericentral cells of uniform length. These branches are covered by a cortication of small cells.

Figure 121. Vertebrata fruticulosa. (a) underwater photo; (b) thallus detail (40×); (c) cross section (100×). Reprinted from [17].

5.2. Cylindrical Hollow

Bornetia secundiflora (J. Agardh) Thuret (Figure 122).

Order: Ceramiales; Family: Wrangeliaceae.

Synonym: Griffithsia secundiflora J. Agardh 1841.

Habitat: On rocks and rock pools, lower-intertidal and shallow subtidal.

Description: Thallus scarlet red, densely tufted-filamentous, to 10–15 cm high, upright-congested, solid somewhat membranous-gelatinous consistency. The frond is formed by cylindrical axes about 1 mm in diameter at the bottom, which are slightly attenuated at the extremities, ending obtuse. These axes branch out, at some distance from the base, several times in a dichotomous or sub-dichotomous manner. The entire frond presents a very apparent transversal partition, visible to the naked eye, which delimits elongated-cylindrical segments (3–4 times longer than wide, sometimes slightly barrel-shaped). The reproductive structures are located in the terminal parts surrounded by short, curved branches, in the form of an involucre. Creeping thallus parts with rhizoidal holdfast.

Figure 122. Bornetia secundiflora. Scale on images (b,c): 1 division = 1 mm; (a) field photo; (b) general view; (c) thallus detail with reproductive structure. Reprinted from [17].

Catenella caespitosa (Withering) L.M. Irvine 1976 (Figure 123).

Order: Gigartinales; Family: Caulacanthaceae.

Synonym: Catenella repens (Lightfoot) Batters 1902.

Common name: Creeping chain weed.

Habitat: Typically found at the middle to upper levels of rocky shores, favoring sheltered and shaded environments. It can occasionally be spotted in estuaries and often grows alongside Gelidium pusillum, a species with which it is sometimes mistaken.

Description: A small, dark purple, moss-like plant with highly branched, irregular fronds. The fronds are intermittently constricted into segments of varying sizes, while the holdfast consists of a dense tangle of fibers.

Figure 123. Catenella caespitosa. Scale on image (a): 1 division = 1 mm; (a) general view; (b) microscopic observation (10×), reprinted from [17]; (c) Havey’s illustration, reprinted from [18], public domain.

Champia parvula (C. Agardh) Harvey 1853 (Figure 124).

Order: Rhodymeniales; Family: Champiaceae.

Synonym: Chondria parvula C. Agardh 1824.

Common name: Barrel weed.

Habitat: Epiphytic on smaller algae in lower intertidal pools and subtidal zones.

Description: This species features soft, gelatinous fronds of pinkish-red coloration, highly branched and densely matted, with blunt apices. Fronds can reach up to 100 mm in height. The axes are segmented by nodal diaphragms, with segments approximately as broad as they are long and filled with watery mucilage.

Figure 124. Champia parvula. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Dumontia contorta (S.G. Gmelin) Ruprecht 1850 (Figure 125).

Order: Gigartinales; Family: Dumontiaceae.

Synonym: Dumontia incrassata (O.F. Müller) J.V. Lamouroux 1813.

Common name: Dumont’s Tubular Weed.

Habitat: A marine species commonly found on rocks and pebbles in shallow open pools, ranging from the upper intertidal to shallow subtidal zones. It is widely distributed and frequently encountered.

Description: The erect thallus begins as cylindrical in its juvenile stage and gradually becomes compressed with age. It is tubular and hollow, with coloration ranging from brown-red to deep crimson-purple, often fading to yellow-brown at the tips. The thallus bears irregular, simple lateral branches that taper at both ends, sometimes appearing slightly swollen and frequently twisted along the longitudinal axis. Its texture is soft and gelatinous. The holdfast is a small, persistent disk that expands as the plant matures.

Figure 125. Dumontia contorta. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Gastroclonium ovatum (Hudson) Papenfuss 1944 (Figure 126).

Order: Rhodymeniales; Family: Champiaceae.

Synonym: Lomentaria ovalis (Hudson) Zanardini 1840.

Common name: Red Grape Weed.

Habitat: A marine species commonly found on rocks and pebbles in shallow open pools, ranging from the upper intertidal to shallow subtidal zones. It is widely distributed and frequently encountered.

Description: The erect thallus begins as cylindrical in its juvenile stage and gradually becomes compressed with age. It is tubular and hollow, with coloration ranging from brown-red to deep crimson-purple, often fading to yellow-brown at the tips. The thallus bears irregular, simple lateral branches that taper at both ends, sometimes appearing slightly swollen and frequently twisted along the longitudinal axis. Its texture is soft and gelatinous. The holdfast is a small, persistent disk that expands as the plant matures. It shows short branches which are hollow with bladder-like or vesicle-like branches—rather elongate with a single joint.

Figure 126. Gastroclonium ovatum. Scale on image (b): 1 division = 1 mm; (a) field photo, (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Gastroclonium reflexum (Chauvin) Kützing 1849 (Figure 127).

Order: Rhodymeniales; Family: Champiaceae.

Synonym: Lomentaria reflexa Chauvin 1831.

Common name: Reflexed Grape Weed.

Habitat: Predominantly epilithic and epiphytic, particularly on Corallina, inhabiting the littoral and upper sublittoral zones in sandy, well-lit pools.

Description: This small alga reaches approximately 6 cm in length, with fronds emerging from a branched holdfast that reflex and form haptera upon contact with the rock. Its hollow, terete branches extend up to 6 cm and are segmented by septa, creating a beaded appearance. Secondary branching follows a dichotomous, distichous pattern. The species exhibits a dark purplish-red coloration and bears a strong resemblance to Chylocladia verticillata, with which it may be mistaken. Spermatangia, cystocarps, and polysporangia have been observed.

Figure 127. Gastroclonium reflexum. (a) underwater photo, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Lomentaria articulata (Hudson) Lyngbye (Figure 128).

Order: Rhodymeniales; Family: Lomentariaceae.

Synonym: Chondria articulata (Hudson) C. Agardh 1817.

Common names: Bunny Ears, Bunny-eared Bead Wee.

Habitat: On rocks, lower intertidal and subtidal.

Description: Crimson to brownish red fronds, generally of intense red color, soft, mucilaginous, cylindrical, to 10–20 cm long. Axis of hollow section, branched of dichotomous way and often whorled, and regularly divided in ovoid segments by quite marked constrictions, which give it an articulated aspect; articles of variable size. The upper part of the thallus with groups of branches often ending in two twigs whose arrangement resembles that of a rabbit’s ears. Base of creeping rhizoidal filaments. Similar gametophyte and tetrasporophyte.

Figure 128. Lomentaria articulata (Hudson) Lyngbye (Rhodophyta). Scale on photos (b,c): 1 division = 1 mm; (a) underwater photo; (b) general view; (c) axes with constrictions. Reprinted from [17].

Lomentaria clavellosa (Lightfoot ex Turner) Gaillon 1828 (Figure 129).

Order: Rhodymeniales; Family: Lomentariaceae.

Synonym: Chylocladia clavellosa (Turner) Hooker 1833.

Common names: Club bead-weed, Feathery tube weed.

Habitat: A marine species commonly found on rocks and stones in pools, the lower intertidal, and subtidal zones. It is widely distributed and frequently encountered.

Description: Soft, slightly flattened fronds with a vibrant pinkish-red hue, reaching up to 400 mm in height. The main axis typically bears numerous distichous branches, sometimes appearing only in apical tufts. The ultimate branchlets feature spindle-shaped ramuli, with no obvious constrictions present on any part of the frond.

Figure 129. Lomentaria clavellosa. Scale on photo (b): 1 division = 1 mm; (a) general appearance (reprinted with permission from Ignácio Bárbara); (b) herbarium specimen reprinted from [17].

5.3. Cylindrical Thick

Caulacanthus ustulatus (Mertens ex Turner) Kützing (Figure 130).

Order: Gigartinales; Family: Caulacanthaceae.

Synonym: Caulacanthus divaricatus (Suhr) Papenfuss 1943.

Habitat: On rock and on mussels, mostly on upper but also on mid-intertidal.

Description: Reddish-brown in color, darkening to black upon desiccation. Forms dense, entangled tufts that are rough to the touch and can reach up to 5 cm in height. The plant is anchored by cylindrical, creeping axes, from which additional axes emerge—also cylindrical in cross section and irregularly branched. Branches (ramifications) terminate in acute apices, often bearing small spines.

Figure 130. Caulacanthus ustulatus. Scale on images (a): 1 division = 1 mm; (a) field photo; (b) apexes with spines. Reprinted from [17].

Chondracanthus acicularis (Roth) Fredericq (Figure 131).

Order: Gigartinales; Family: Gigartinaceae.

Synonym: Gigartina acicularis (Roth) J.V. Lamouroux 1813.

Common name: Creephorn.

Habitat: On rocks in the intertidal zone. It tends to form extensive tufts or carpets in the middle and lower-intertidal.

Description: Purple-red or blackish, cartilaginous, cylindrical, to 10 cm long. Irregularly bipinnately branched, branches curved, sharply pointed. Discoid base, often stoloniferous and entangled.

Figure 131. Chondracanthus acicularis. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) general view, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Chondria coerulescens (J. Agardh) Sauvageau (Figure 132).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Chondriopsis coerulescens J. Agardh 1863.

Common name: Iridescent cartilage weed.

Habitat: Found on sand-covered rocks in the low to mid intertidal zone.

Description: Bluish or yellowish in color with a distinctive blue iridescence, turning black upon drying. Young axes exhibit a striking turquoise iridescence when alive. The thallus is cartilaginous, flexible, and cylindrical. Erect axes, either isolated or forming dense tufts, range from 3 to 8 cm in height, with the main axis measuring 0.4–0.5 mm in diameter. Branching occurs sparsely at irregular intervals in a spiral pattern, extending to one to three orders of branching. Branches are linear with rounded apices, attenuated at the point of insertion, often elongated and curving downward. Attachment is achieved through a system of interlaced cylindrical axes.

Figure 132. Chondria coerulescens. Scale on image (c): 1 division = 1 mm; (a) underwater photo; (b) specimen detail; (c) details of the branches and apices. Reprinted from [17].

Chondria scintillans Feldmann-Mazoyer 1964 (Figure 133).

Order: Ceramiales; Family: Rhodomelaceae.

Habitat: The area between the high and low tide lines, characterized by alternating exposure to air and submersion due to tidal fluctuations. This zone typically extends from the shoreline down to depths of approximately 15 m.

Description: The species name “scintillans” refers to the iridescent surface of the red algae.

Figure 133. Chondria scintillans. (a) underwater photo; (b) general view. Reprinted from [17].

Chondria dasyphylla (Woodward) C. Agardh (Figure 134).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Laurencia dasyphylla (Woodward) Greville 1830.

Common names: Diamond cartilage weed.

Habitat: on rocks, sometimes at pools covered by sand, lower-intertidal and subtidal.

Description: Thallus red, reddish-brown or purple, sometimes discolored to pink, up to 20 cm in height and of cartilaginous consistency. It is fixed by a tangle of creeping axes from which erect cylindrical axes depart, on which are alternately, or opposite side branches whose length decreases toward the terminal parts of the axis; these branches carry short branchlets, club-shaped, slightly curved, with rounded apices that are clearly attenuated at the point of insertion, similarly to the branches.

Figure 134. Chondria dasyphylla. Scale on image (c): 1 division = 1 mm; (a) underwater photo; (b) specimen detail; (c) club-shaped branches. Reprinted from [17].

Chylocladia verticillata (Lightfoot) Bliding 1928 (Figure 135).

Order: Rhodymeniales; Family: Champiaceae.

Synonym: Kaliformia verticillata (Lightfoot) Stackhouse 1816.

Common name: Juicy Whorl Weed.

Habitat: On rocks and stones and epiphytic, lower intertidal and subtidal.

Description: The fronds are soft and gelatinous, forming cylindrical structures that range in color from pinkish to brown-red. In sunlit environments, they may appear bleached yellow or nearly white. Growing up to 300 mm in height, they contain watery mucilage. The main axis is simple and joined, featuring nodal diaphragms with slight constrictions at the nodes. Each node bears two or more branches, which themselves may be further branched, ending in small, beaded ultimate ramuli. The branching pattern is highly variable, with plants from exposed coastal areas often exhibiting a simpler form with small terminal tufts of ramuli.

Figure 135. Chylocladia verticillata. Scale on image (b): 1 division = 1 mm; (a) detail of tetrasporophyte (reprinted with permission from Ignácio Bárbara); (b) herbarium specimen, reprinted from [17].

Furcellaria lumbricalis (Hudson) J.V. Lamouroux 1813 (Figure 136).

Order: Gigartinales; Family: Furcellariaceae.

Synonym: Sphaerococcus fastigiatus (Linnaeus) Wahlenberg 1826.

Common name: Clawed forkweed.

Habitat: This species thrives on rocky surfaces in the lower intertidal and shallow subtidal zones, frequently found in pools within open areas. It is commonly seen on sandy and muddy shores, demonstrating an ability to tolerate reduced salinity levels.

Description: This species has a cartilaginous texture and features cylindrical, brownish-black fronds that are repeatedly dichotomously branched and fastigiate. Fronds can reach up to 2 mm in diameter and 300 mm in length, terminating in sharply pointed apices. The plant anchors itself via extensively branched rhizoids. Structurally multiaxial, its medulla is composed of cylindrical cells interspersed with rhizoids, while the cortex consists of irregular filaments. Inner cortical cells are elliptical, whereas the outer cells are narrow, elongated, and arranged in radial rows.

Figure 136. Furcellaria lumbricalis. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

Gracilaria gracilis (Stackhouse) M. Steentoft, L.M. Irvine & W.F. Farnham (Figure 137).

Order: Gracilariales; Family: Gracilariaceae.

Synonym: Gracilaria verrucosa var. procerrima (Esper) M.P. Reis, nom. inval. 1981.

Common name: Slender wart weed.

Habitat: On rocks and stones, intertidal and subtidal, especially on sandy shores.

Description: Dark crimson-brownish-red, greenish translucent or yellowish to brown, green; cartilaginous, cylindrical, to 10–30 (60 cm) long. Diameter of axes 0.5–3 mm, branching very irregular, sparse or profuse, rising from small, fleshy, perennial discoid holdfast; apices pointed. With or without hemispherical wart-like cystocarps.

Gymnogongrus griffithsiae (Turner) Kützing (Figure 138).

Figure 137. Gracilaria gracilis. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) specimen detail; (c) cross section with cystocarp (40×). Reprinted from [17].

Order: Gigartinales; Family: Phyllophoraceae.

Synonym: Sphaerococcus griffithsiae (Turner) C. Agardh 1817.

Habitat: On sand-covered rocks; upper to mid intertidal.

Description: Brow-red to blackish purple, stiff-erect, cartilaginous, cylindrical to compressed, to 7.5 cm high, repeatedly dichotomous, with rounded, somewhat flattened apices; expanded discoid base.

Figure 138. Gymnogongrus griffithsiae. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) several specimens. Reprinted from [17].

Rhodomela confervoides (Hudson) P.C. Silva 1952 (Figure 139).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Sphaerococcus confervoides (Hudson) C. Agardh 1817.

Common name: Straggly Bush weed.

Habitat: Found on rocks and shells within intertidal pools across all tidal levels. Widely distributed and commonly occurring.

Description: The fronds of this species are cylindrical, cartilaginous, and bushy, exhibiting a brownish-red coloration and reaching lengths of up to 300 mm. The fronds are repeatedly and irregularly branched, with branches adorned by small, pinnate branchlets and simple, pointed ramuli. In winter, the branchlets are shed, leaving the frond bare and spiky—creating a stark contrast to its fuller summer form. Internally, a central siphon is surrounded by elongated cells, with an outer layer composed of small, pigmented cells. Articulations are present but remain indistinct.

Figure 139. Rhodomela confervoides. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) specimen detail. Reprinted from [17].

Scinaia furcellata (Turner) J. Agardh (Figure 140).

Order: Nemaliales; Family: Scinaiaceae.

Synonym: Chondria furcellata (Turner) C. Agardh 1817.

Common name: Southern Scinà’s Weed.

Habitat: On rocks, stones and shells; in lower-intertidal pools and channels (generally with sandy deposits) and subtidal.

Description: Reddish brown to pink fronds, gelatinous but firm, cylindrical, 1–3 mm diameter, to 10 cm long, dichotomously branched (several times in several planes giving the border a bulky corymbiform aspect) from small discoid base. Constrictions at irregular intervals in mature fronds; acute apices but rounded at the end.

Figure 140. Scinaia furcellata (Turner) J. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) specimen detail. Reprinted from [17].

Gigartina pistillata (S.G. Gmelin) Stackhouse (Figure 141).

Order: Gigartinales; Family: Gigartinaceae.

Synonym: Gelidium gigartinum (Linnaeus) Lyngbye 1819.

Common name: Pestle weed.

Habitat: Lower intertidal and subtidal, supports the presence of sand.

Description: Dark-red or red brown, almost black, erect, up to 20 cm high, cartilaginous, somewhat elastic, attached through a small basal disk. Dichotomously branched into a plane; compressed stipes which are progressively transformed into axis of oval or elliptical section. Tetrasporocysts are in the form of small bumps; cystocarps spherical (up to 3 mm of diameter) in short simple or bifid thalli.

Figure 141. Gigartina pistillata. Scale on images (b,c,e): 1 division = 1 mm; (a) field photo; (b) tetrasporophyte; (c) tetrasporangial sori; (d) female gametophyte; (e) female gametophyte with cystocarps. Reprinted from [17].

Hypnea musciformis (Wulfen) J.V. Lamouroux 1813 (Figure 142).

Order: Gigartinales; Family: Cystocloniaceae.

Synonym: Sphaerococcus divaricatus C. Agardh 1827.

Common names: Hook weed, Hooked seaweed, Hypnea.

Habitat: Typically found in calm intertidal zones and shallow subtidal reef flats, as well as tidepools and rocky intertidal benches. Most commonly occurs in the lower intertidal to shallow subtidal reef flats, where it attaches to sandy flat rocks.

Description: Usually red in coloration, though it may appear yellowish-brown under high light exposure or in nutrient-poor environments. It forms clumps or masses of loosely intertwined cylindrical branches, measuring 10–20 cm in height and 0.5–1.0 cm in diameter, gradually tapering toward the tips. The structure is firm, cartilaginous, and highly branched, with branching patterns that are often irregular, tendril-like, and twist around the axes of other algae. Many branches and axes terminate in broad, flattened hooks. Holdfasts are either small and inconspicuous or entirely absent.

Figure 142. Hypnea musciformis. Scale on image: 1 division = 1 mm; herbarium specimen. Reprinted from [17].

Nemalion elminthoides (Velley) Batters 1902 (Figure 143).

Order: Nemaliales; Family: Nemaliaceae.

Synonym: Palmella elminthoides (Withering) S.F. Gray 1821.

Common names: Sea Noodle, Sea Noodles, Threadweed.

Habitat: On exposed rocky shores, generally epilithic in the tidal zone in clear waters.

Description: The thallus is cylindrical and ranges in color from reddish to purple-brown. It has a softly gelatinous texture and can be simple or sparsely dichotomously branched. Measuring up to 2 mm in width and reaching lengths of 250 mm, it is anchored by a discoid holdfast.

Figure 143. Nemalion elminthoides. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Pseudopolyides furcellarioides Gallardo, I. Bárbara & Cremades 2013 (Figure 144).

Order: Gigartinales; Family: Cruoriaceae.

Habitat: Found on rocky substrates from the lower intertidal zone to the upper subtidal, thriving in both exposed and semi-exposed environments. It demonstrates resilience by tolerating the sand cover.

Description: These plants range from 5 to 23 cm in height, exhibiting hues from brownish-black to purplish-red, appearing brown when viewed under incandescent transmitted light. The thalli are cartilaginous and terete, with vegetative branches measuring between 1100 and 2100 µm in diameter. Branching is predominantly dichotomous, occasionally trichotomous, extending up to eight orders, and Some axes are compressed.

Figure 144. Pseudopolyides furcellarioides. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen (all reprinted with permission from Ignácio Bárbara).

Sphaerococcus coronopifolius Stackhouse 1797 (Figure 145).

Order: Gigartinales; Family: Sphaerococcaceae.

Synonym: Coronopifolia coronopifolia Le Jolis 1896.

Common name: Berry Wart Cress.

Habitat: Rarely found on rocks in the lower intertidal zone, but often common in the shallow subtidal, down to depths of 15 m.

Description: This species displays narrow, compressed, two-edged cartilaginous fronds with a vivid scarlet coloration. The main axes are dark brownish-red and can reach lengths of up to 300 mm. Branching is abundant and occurs in dichotomous, sub-dichotomous, or alternate patterns. Terminal branchlets are acute and often bear short marginal proliferations. The tetrasporophyte stage, Haematocelis fissurata, manifests as a thick crust with oily fissures and is occasionally found in association with this species.

Figure 145. Sphaerococcus coronopifolius. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

5.4. Flattened Thick Red Macroalgae

Ahnfeltiopsis devoniensis (Greville) P.C. Silva & De Cew (Figure 146).

Order: Gigartinales; Family: Phyllophoraceae.

Synonym: Gymnogongrus devoniensis (Greville) Schotter 1968.

Common name: Devonshire fan weed.

Habitat: On rocks, intertidal pools, lower intertidal or shallow sublittoral.

Description: A. devoniensis is difficult to distinguish from Gymnogongrus crenulatus; however, it typically exhibits smaller dimensions, with a maximum length of around 10 cm. Its branches have parallel sides, and the reproductive structures (cystocarps) are internal. The species forms a brownish-red, medium-sized flattened frond with regular dichotomous branching, anchored by disk-like holdfasts approximately 3 mm in diameter.

Figure 146. Ahnfeltiopsis devoniensis. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) general view; (c) cross section of two blades showing the internal reproductive structures (cystocarps) (40×). Reprinted from [17].

Calliblepharis ciliata (Hudson) Kützing 1843 (Figure 147).

Order: Gigartinales; Family: Cystocloniaceae.

Synonym: Rhodymenia ciliata (Hudson) Greville 1830.

Common name: Eyelash Weed.

Habitat: Larger lower intertidal pools and subtidal (0–25 m) on stones, maerl and shells, widely distributed, common in south and west, sometimes frequent in drift.

Description: Flattened, subcartilaginous fronds of purple-red coloration, reaching up to 300 mm in length and 20–70 mm in width. Fronds are lanceolate or forked, with irregular pinnate branching. In maturity (typically during summer), the margins and surface become covered with short, stiff proliferations. A short, cylindrical stipe emerges from a creeping, branched holdfast.

Figure 147. Calliblepharis ciliata. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen. Reprinted from [17].

Calliblepharis jubata (Goodenough & Woodward) Kützing 1843 (Figure 148).

Order: Gigartinales; Family: Cystocloniaceae.

Synonym: Calliblepharis lanceolata Batters 1902.

Common name: False Eyelash Weed.

Habitat: Occurs on rocks and as an epiphyte, typically found from the mid-intertidal to shallow subtidal zones.

Description: Dark brown-red, cartilaginous but flaccid, up to 30 cm long. Stipe more or less cylindrical, to 10 cm long; sparingly branched rhizoidal holdfast. Blade lanceolate, to 15 cm wide, simple, irregularly pinnate or dichotomously divided, clothed with tendril-like coiled or hooked proliferations, to 10 cm (or more) long; surface with small spinous excrescences in well-developed specimens.

Figure 148. Calliblepharis jubata. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Chondrus crispus Stackhouse 1797 (Figure 149).

Order: Gigartinales; Family: Gigartinaceae.

Synonym: Gymnogongrus norvegicus (Gunnerus) J. Agardh 1851.

Common names: Irish moss, Carragheen, Carragheen moss, Dorset weed, Pearl moss, Sea moss, Sea pearl moss, Jelly moss, Rock moss, Gristle moss, Curly moss, Curly gristle moss, Carrageen, Carraghean, Carrageenin.

Habitat: On rocks, lower intertidal and shallow subtidal; in pools in the mid-intertidal.

Description: Dark purplish-red, red, yellowish or greenish, gametophytes are often iridescent under water, cartilaginous, up to 22 cm high. Stipe compressed, narrow, expanding gradually to a flat, fan-like blade, repeatedly dichotomously branched, in tufts. Axils rounded, apices rounded or truncated, fronds thicker in central zone than margins. Reproductive structures (namely to the female gametophytes fruiting bodies (carposporangia) that occur in cystocarps that protrude strongly).

Figure 149. Chondrus crispus. Scale on images (b,c): 1 division = 1 mm; (a) underwater photo; (b) tetrasporophyte; (c) female gametophyte. Reprinted from [9].

Chondracanthus teedei (Mertens ex Roth) Kützing 1843 (Figure 150).

Order: Gigartinales; Family: Gigartinaceae.

Synonym: Gigartina teedei (Mertens ex Roth) J.V. Lamouroux 1813.

Common name: Shikin-nori.

Habitat: On rocks below the intertidal zone.

Description: The upper thallus branches are cylindrical, while the lower ones are flattened, displaying a dark crimson to black-red hue. They exhibit irregular-pinnate branching, repeatedly extending in a cartilaginous-firm manner. The lateral branches are widely spaced and sharply pointed, with the youngest terminal sections resembling thorns. The base is discoid in shape.

Figure 150. Chondracanthus teedei. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [12]; (c) Harvey’s illustration, reprinted from [18], public domain.

Chondracanthus teedei var. lusitanicus (J.E. De Mesquita Rodrigues) Bárbara & Cremades (Figure 151).

Order: Gigartinales; Family: Gigartinaceae.

Synonym: Gigartina teedei var. lusitanica J.E. De Mesquita Rodrigues 1958.

Habitat: On rocks and intertidal pools, generally in shallow water.

Description: This variety of C. teedei was first described by Mesquita Rodrigues (1958) from specimens collected in Buarcos Bay (Figueira da Foz, Portugal). C. teedei typically presents flattened main axes with regular pinnate branching. The fronds are cartilaginous and membranous, exhibiting a purplish-violet color that darkens upon desiccation and turns greenish-yellow as it decays.

However, specimens collected in Buarcos Bay show distinct morphological differences compared to those from Brittany (France), Barcelona (Spain), and the Mediterranean Sea. The principal axes of the fronds and their ramifications are notably broader—reaching up to 1 cm in older portions—resulting in a more robust appearance. These fronds often attain lengths of up to 20 cm. Additionally, the branching is denser and more luxuriant, with pinnules developing not only along the margins of the branches but also across their surfaces.

Figure 151. Chondracanthus teedei var. lusitanicus. Scale on images (b–e): 1 division = 1 mm; (a) underwater photo; (b) general view; (c) non-fructified thallus; (d) tetrasporophyte; (e) fructified female gametophyte. Reprinted from [17].

Dilsea carnosa (Schmidel) Kuntze 1898 (Figure 152).

Order: Gigartinales; Family: Dumontiaceae.

Synonym: Sarcophyllis edulis (Stackhouse) J. Agardh 1876.

Common name: Red Rags.

Habitat: Marine species, on rock in shady pools, lower intertidal on rock, and shallow subtidal to 25 m, usually on rock in kelp forests; widely distributed, common.

Description: These foliose red algae are dark red, often transitioning to yellow in their upper regions. As the thickest of their kind in the North Atlantic, they feature flattened, cartilaginous fronds that emerge in varied sizes—small, medium, and large—from a robust, discoid holdfast. Their fronds are obtuse and ovate, tapering at the base, reaching up to 500 mm in length and 250 mm in width. Reproduction takes place during the depths of winter.

Figure 152. Dilsea carnosa. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Gelidium corneum (Hudson) J.V. Lamouroux 1813 (Figure 153).

Order: Gelidiales; Family: Gelidiaceae.

Synonym: Gelidium sesquipedale (Clemente) Thuret 1876.

Common names: Kanteen, Giant Gelidium, Atlantic Agar.

Habitat: On rocks and tide pools in exposed areas.

Description: This species exhibits a dark red hue with a firm, cartilaginous texture. Its thalli can grow up to 30 cm in length, featuring branches with an obtuse apex that taper at the base. It commonly forms dense clusters of fronds, often thriving beneath a protective kelp canopy.

Figure 153. Gelidium corneum. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Greville’s illustration, reprinted from [27], public domain.

Gelidium pulchellum (Turner) Kützing (Figure 154).

Order: Gelidiales; Family: Gelidiaceae.

Synonym: Gelidium latifolium var. pulchellum (Turner) Van Heurck 1908.

Habitat: Found in and around tidal pools within the mid- and lower-intertidal zones.

Description: Fronds are dark red-brown, cartilaginous, and range from 5 to 10 cm in height. They exhibit regular or irregular bipinnate branching and arise from a creeping base. The main axes are narrow and cylindrical, becoming somewhat flattened toward the upper portions. Ultimate branches are initially short and pointed, later becoming pathulate, especially during reproductive stages. Overall appearance varies depending on habitat conditions and seasonal changes.

Figure 154. Gelidium pulchellum. Scale on image (c): 1 division = 1 mm; (a) underwater photo; (b) general view; (c) detail; (d) spathulate branches from a tetrasporophyte (40×); (e) detail from (d) photo (100×). Reprinted from [17].

Gelidium pusillum (Stackhouse) Le Jolis 1863 (Figure 155).

Order: Gelidiales; Family: Gelidiaceae.

Synonym: Gelidium repens Okamura 1899.

Common name: Hai-tengusa.

Habitat: A marine and estuarine species occurring in rock pools and on sandy rocks, especially in environments with widely fluctuating salinities, such as those typical of upper-shore zones.

Description: This species has a cartilaginous texture and appears in shades of purplish to blackish red. It forms dense turf-like structures, reaching heights of 2 to 10 mm, emerging from a creeping base that integrates shell fragments and small mollusks. Its erect fronds are flattened, leaf-like, and range from 0.5 to 2 mm in width.

Figure 155. Gelidium pusillum. Scale on image (a): 1 division = 1 mm; (a,b) microscopic observation (40×). Reprinted from [17].

Gelidium spinosum (S.G. Gmelin) P.C. Silva (Figure 156).

Order: Gelidiales; Family: Gelidiaceae.

Synonym: Gelidium latifolium (Greville) Bornet 1883.

Habitat: In and around tidal pools in mid- and lower-intertidal.

Description: A small cartilaginous alga, typically crimson to purplish-red in color, measuring 20–60 mm in length. The main axes are distinctly flattened and often narrower at the base. Ultimate branches are short, frequently opposite, and may be spine-like or spathulate in form.

Figure 156. Gelidium pulchellum. Scale on image (c): 1 division = 1 mm; (a) general view; (b) underwater photo; (c) herbarium specimen. Reprinted from [17].

Gracilaria multipartita (Clemente) Harvey (Figure 157).

Order: Gracilariales; Family: Gracilariaceae.

Synonym: Chondrus multipartitus (Clemente) Greville 1833.

Common name: Cleaved wart weed.

Habitat: On rocks or other hard substrata, tolerant to sand, intertidal and subtidal.

Description: Translucent, dull purple to reddish-brown in color, reaching up to 25 cm in length. The thallus is cartilaginous and very brittle. The compressed stipe gradually expands into a blade, which may be up to 1 mm thick and approximately 1 cm wide between dichotomies. The stipe branches up to six times within the plane of the blade. The blade margins are frequently proliferous.

Figure 157. Gracilaria multipartita. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) general view. Reprinted from [17].

Grateloupia filicina (J.V. Lamouroux) C. Agardh (Figure 158).

Order: Halymeniales; Family: Grateloupiaceae.

Synonym: Delesseria filicina J.V. Lamouroux 1813.

Common name: Chop-chop.

Habitat: On rocks, in rock pools (sometimes with sand), from mid-intertidal to shallow subtidal.

Figure 158. Grateloupia filicina. Scale on images (b,c): 1 division = 1 mm; (a) field photo; (b) general view; (c) marginal proliferations. Reprinted from [17].

Gymnogongrus crenulatus (Turner) J. Agardh (Figure 159).

Order: Gigartinales; Family: Phyllophoraceae.

Synonym: Actinococcus peltaeformis F. Schmitz 1893.

Common name: Norwegian fan weed.

Habitat: On rocks, lower littoral and subtidal, tolerant of sand cover; plants typically encrusted with Bryozoan, Foraminifera and calcareous algae.

Description: Dark red fronds, to 10 cm high, cartilaginous, fleshy, flattened, with short cylindrical stipe from basal disk. Repeatedly dichotomous, branches strap-shaped with parallel margins, often longitudinally twisted. Apices rounded, often paler than the rest of the frond. Reproductive structures appear as external, wart-like excrescences (tetrasporoblasts).

Figure 159. Gymnogongrus crenulatus. (a) underwater photo; (b) detail of tetrasporoblasts; (c) tetra-sporoblast transversal section (50×). Reprinted from [17].

Hildenbrandia rubra (Sommerfelt) Meneghini 1841 (Figure 160).

Order: Hildenbrandiales; Family: Hildenbrandiaceae.

Synonym: Hildenbrandia rosea Kützing 1843.

Habitat: This species is found on rocks and stones across all tidal levels, frequently appearing in splash zones within caves and extending into subtidal areas. It is widely distributed and highly abundant, especially in upper shore regions.

Description: H. rubra forms thin, tightly adherent sheets on rocky substrates, creating a continuous layer that is difficult to remove without breaking the underlying rock. It has a leathery consistency and a smooth surface, punctuated by small elevations corresponding to conceptacles. This dark red to nearly black alga grows slowly, forming extensive patches that can be widespread. At times, it may be difficult to determine whether one is observing a single large individual or several smaller ones.

Figure 160. (a) underwater photo (reprinted with permission from Ignácio Bárbara); (b) Harvey’s illustration, reprinted from [18], public domain.

Laurencia obtusa (Hudson) J.V. Lamouroux 1813 (Figure 161).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Chondria obtusa (Hudson) C. Agardh 1817.

Common name: Rounded brittle fern.

Habitat: Occurs on solid substrata in extremely shallow areas of calm water, as well as in exposed locations within the intertidal zone.

Description: Plants form a bushy structure with green or yellow axes and rose-colored branchlets, reaching 1.5 to 2.5 mm in diameter. The main stems are long and sparsely branched in an alternate pattern, measuring 0.75 to 1.50 mm in diameter. Toward the upper portions, branching becomes denser and more widely spreading in a paniculated arrangement. The smallest branches, along with the short, truncated ultimate branchlets, are either opposite or sub-verticillate, ranging from 0.5 to 0.75 mm in diameter. Tetrasporangia are arranged in a band just below the apex of the slightly modified branchlets.

Figure 161. Laurencia obtusa. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Laurencia pyramidalis Bory ex Kützing 1849 (Figure 162).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Laurencia obtusa var. pyramidata Bory ex J. Agardh 1852.

Common name: Pyramidal Fern-weed.

Habitat: Usually epiphytic, annual, lower intertidal.

Description: Species known for its distinctive pyramidal or conical shape and bushy thallus. It typically grows to a height of about 10 cm, exhibiting a bright red to pinkish color. This alga is found in shallow waters, often between 1 and 20 m deep, and prefers rocky substrates, reefs, and coral rubble where it can form dense populations.

Figure 162. Laurencia pyramidalis. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) several specimens with scale. Reprinted from [17].

Metacallophyllis laciniata (Hudson) A. Vergés & L.Le Gall 2017 (Figure 163).

Order: Gigartinales, Family: Kallymeniaceae.

Synonym: Callophyllis laciniata (Hudson) Kützing 1843.

Common names: Beautiful fan weed, Fanweed.

Habitat: On rock or epiphytic on Laminaria hyperborea holdfasts, shady pools of lower intertidal or subtidal.

Description: Occurs on solid substrata in extremely shallow areas of calm water, as well as in exposed locations within the intertidal zone.

Description: Plants form a bushy structure with green or yellow axes and rose-colored branchlets, reaching 1.5 to 2.5 mm in diameter. The main stems are long and sparsely branched in an alternate pattern, measuring 0.75 to 1.50 mm in diameter. Toward the upper portions, branching becomes denser and more widely spreading in a paniculated arrangement. The smallest branches, along with the short, truncated ultimate branchlets, are either opposite or sub-verticillate, ranging from 0.5 to 0.75 mm in diameter. Tetrasporangia are arranged in a band just below the apex of the slightly modified branchlets.

Figure 163. Metacallophyllis laciniata. Scale on image (b): 1 division = 1 mm, (a) field photo; (b) herbarium specimen. Reprinted from [17].

Mastocarpus stellatus (Stackhouse) Guiry (Figure 164).

Order: Gigartinales; Family: Phyllophoraceae.

Synonym: Gigartina stellata (Stackhouse) Batters 1902.

Common names: Grape pip weed; False Irish-moss.

Habitat: On rocks in the intertidal zone. Tends to form extensive tufts in the upper intertidal.

Description: Dark reddish-brown to purplish brown, cartilaginous, often in dense tufts, up to 17 cm high. Fronds dichotomously branched, channeled with thickened margins and widened from a narrow stipe, discoid holdfast. Female gametophyte: upper part of frond with papillae (1 cm long or more) on surfaces and margins, male gametophyte: lack papillae; generally rare; tetrasporophyte: purplish-black crust (Petrocelis cruenta phase).

Figure 164. Mastocarpus stellatus. (a) field photo; (b) cystocarps surface detail; (c) Petrocelis cruenta phase. Reprinted from [17].

Osmundea hybrida (De Candolle) K.W. Nam 1994 (Figure 165).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Laurencia hybrida (A.P. de Candolle) T. Lestiboudois 1827.

Common name: False Pepper Dulse.

Habitat: This marine species inhabits stones and shells, occasionally growing epiphytically. Found in the upper intertidal zone, it is widely distributed and frequently encountered in local environments.

Description: The fronds are cylindrical, cartilaginous, and tufted, ranging in color from dark purple to greenish yellow, and reaching a length of 150 mm. The main axis exhibits repeatedly pinnate branching, with predominantly alternate branches that shorten towards the apex, forming a pyramidal outline. The ultimate ramuli are short, spreading, and truncate. The axis is mono-siphonous, containing elongated pericentral cells and one to two outer layers of rounded, pigmented cells. The apex is concave, encircled by ephemeral, colorless dichotomous hairs that surround the apical cell.

Figure 165. Osmundea hybrida. Scale on images (b): 1 division = 1 mm; (a) general view; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Osmundea pinnatifida (Hudson) Stackhouse (Figure 166).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Laurencia pinnatifida (Hudson) J.V. Lamouroux 1813.

Common name: Pepper dulse.

Habitat: On rocks in the intertidal zone.

Description: Dark red to dark purple (sometimes bleached to yellow-red), cartilaginous, fleshy, erect, compressed/flattened and densely branched fronds with 2–10 cm high and 2–8 mm wide. Main axes robust, basally rounded, branching irregularly alternating in one plane (distichous), in the upper part repeated-pinnate, terminal part short and blunt-rounded; tips have a longitudinal groove (seen with an ×10 lens). Fixed by a disk from where several fronds and stoloniferous branches may arise.

Figure 166. Osmundea pinnatifida. Scale on images (b,c): 1 division = 1 mm; (a) underwater photo; (b) general view; (c) apical fronds. Reprinted from [17].

Palmaria palmata (Linnaeus) F. Weber & D. Mohr 1805 (Figure 167).

Order: Palmariales; Family: Palmariaceae.

Synonym: Rhodymenia palmata (Linnaeus) Greville 1830.

Common names: Crannogh, Dillesk, Dillisk, Dried dulse, Dulse, Sheep Dulse, Shelldulse, Water Leaf.

Habitat: This marine species inhabits rocks and mussels and also grows epiphytically on various algae. It is found across all intertidal levels, with a preference for areas near low water, and extends into shallow subtidal zones, particularly thriving on the upper part of Laminaria hyperborea.

Description: Fronds are reddish-brown, flattened, and range from membranous to leathery in texture. They typically measure 50–300 mm in length, though specimens may occasionally reach up to 1000 mm. Emerging from a discoid base, the fronds usually possess a small stipe that gradually broadens into simple, dichotomously, or palmately divided structures, often adorned with distinctive marginal leaflets. The blade shows considerable morphological variability, with segments ranging from broadly ovate to narrowly linear.

Figure 167. Palmaria palmata. (a) general view, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Plocamium cartilagineum (Linnaeus) P.S. Dixon (Figure 168).

Order: Plocamiales; Family: Plocamiaceae.

Synonym: Gelidium cartilagineum (Linnaeus) Gaillon 1828.

Common names: Cocks comb, Cock’s comb, Branched cock’s comb, Red comb weed.

Habitat: On rocks or epiphyte, at lower intertidal pools, infralittoral up to about 20 m.

Description: Thallus bright scarlet to pinkish reddish brown, membranous consistency, cartilaginous on the axes, up to 30 cm long. Narrow, compressed, tufted, much divided branching fronds. It is fixed from a small basal disk from which a main axis, compressed, 1–4 mm wide, branches alternately in a single plane; the branching occurs alternately along the fronds and becomes more frequent towards the tips. The general appearance of this species can greatly vary from very compact and closely branched to a much broader appearance with widely separated branching. The last branches are arranged, typically, on only one side of the branch that bears them, giving a distinctive feathery or comb-like appearance (pectinate).

Figure 168. Plocamium cartilagineum. Scale on images (b,c): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen; (c) pectinate branches. Reprinted from [17].

Plocamium suhrii Kützing 1849 (Figure 169).

Order: Plocamiales; Family: Plocamiaceae.

Synonym: Plocamium nobile J. Agardh 1851.

Habitat: Inhabits lower eulittoral rock pools in the shallow sublittoral zone.

Description: These plants range from bright to pale red and can grow up to 15 cm tall. They are complanate and extensively branched, with erect, compressed axes measuring 1.5–2 mm in width. The lateral branchlets form distinct groups, each consisting of one simple and one compound branchlet. Simple branchlets are triangular, reaching up to 4 mm in length and 1.5 mm in width at the base, occasionally displaying a slightly serrated outer margin. Tetrasporangial stichidia are branched two to three times and develop laterally on adventitious branchlets situated in the axils of lateral branchlets.

Figure 169. Plocamium suhrii. (a) Underwater photo; (b) microscopic observation (20×) (all reprinted with permission from Ignácio Bárbara).

Polyneura bonnemaisonii (C. Agardh) Maggs & Hommersand 1993 (Figure 170).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Delesseria bonnemaisonii C. Agardh 1822.

Common name: Crimson Veined Weed.

Habitat: This marine species thrives on rocky surfaces in deep lower intertidal pools, often settling on Laminaria hyperborea stipes. It is widely distributed, with a higher presence along southern and southwestern shores, particularly during summer and autumn.

Description: The fronds are thick, soft, and range in color from deep crimson to rose, turning orange in freshwater. They are translucent, flattened, and fan-shaped, growing up to 300 mm in length. The stipe reaches up to 6 mm, emerging from a flattened discoid base. The blade can be simple or deeply divided into wedge- or ribbon-shaped segments, with a proliferous and undulating margin. Venation is palmate, lacking a distinct midrib, with anastomosing veins. In younger parts, microscopic veins are present.

Figure 170. Polyneura bonnemaisonii. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Pterocladiella capillacea (S.G. Gmelin) Santelices & Hommersand 1997 (Figure 171).

Order: Gelidiales; Family: Pterocladiaceae.

Synonym: Pterocladia capillacea (S.G. Gmelin) Bornet 1876.

Common name: Branched Wing Weed.

Habitat: Marine species, in large pools and lagoons in the lower intertidal and shallow subtidal, widely distributed on south and south-western shores, never common.

Description: With a cartilaginous texture, this dark purplish-red alga features flattened fronds measuring 2 mm in width and reaching up to 200 mm in height. Its branching pattern is pinnate or bipinnate, often bare at the base, with opposite or alternate branches that typically taper at both ends. The distinctive arrangement frequently results in a ‘Christmas-tree’ appearance, while the fronds emerge in a loose tuft from a rhizoidal base.

Figure 171. Pterocladiella capillacea. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Okamura Kintaro illustration, reprinted from [30], public domain.

Pterosiphonia complanata (Clemente) Falkenberg (Figure 172).

Order: Ceramiales; Family: Rhodomelaceae.

Synonym: Polysiphonia complanata (Clemente) J. Agardh 1863.

Common name: Flat winged weed.

Habitat: On rocks (and on sand-covered rocks) and epiphytic, lower intertidal and subtidal.

Description: Dark red thallus, cartilaginous consistency, 5 to 10 cm high. Fixed by rhizoids from which rise compressed axes of 1 to 2 mm wide, branching into a single plane, alternately. Axes bare or scarcely branched in their lower part and carry in the margin’s short spines in the manner of very characteristic saw teeth. From the last, pinnate branches, they alternate, simple at the beginning, later being bifid or multifid. Axes show a polysiphonated structure with a central siphon surrounded by pericentral siphons and outwards by cortical cells (cross section under the microscope).

Figure 172. Pterosiphonia complanata. Scale on images (b,c): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen; (c) detailing of branches. Reprinted from [17].

5.5. Thin Laminate/Foliaceous or in Ribbons Red Macroalgae

Acrosorium ciliolatum (Harvey) Kylin 1924 (Figure 173).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Acrosorium venulosum (Zanardini) Kylin 1924.

Common name: Red Hook Weed.

Habitat: On rocks and epiphytic, lower intertidal and subtidal, widely distributed, occasional.

Description: The fronds are flattened, membranous, and deep red, ranging from 30 to 150 mm in length, occasionally reaching 200 mm. They are deeply segmented into linear-lanceolate sections with irregular branching patterns, often ending in hook-like structures. The margins are toothed and frequently show some degree of proliferation. A network of microscopic veins traverses the fronds, while macroscopic veins are absent.

Figure 173. Acrosorium ciliolatum. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

Apoglossum ruscifolium (Turner) J. Agardh 1898 (Figure 174).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Hypoglossum ruscifolium (Turner) Kützing 1843.

Common name: Veined Tongue Weed.

Habitat: Marine species found on rocks and as an epiphyte in the lower intertidal to subtidal zones. Widely distributed but occurs occasionally.

Description: Fronds are membranous, tufted, and bright red, reaching up to 100 mm in length. Each frond features a conspicuous midrib and wavy margins, up to 6 mm wide, and is repeatedly branched from the midrib. Apices are blunt. Numerous microscopic veins radiate at wide angles from the midrib.

Figure 174. Apoglossum ruscifolium. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Cryptopleura ramosa (Hudson) L. Newton (Figure 175).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Nitophyllum ramosum (Hudson) Batters 1902.

Common name: Fine-veined crinkle weed.

Habitat: On rock and on Laminaria hyperborea stipes, lower intertidal and subtidal.

Description: Brownish red fronds, often iridescent under water, thin, membranous, somewhat papyraceous when older, to 10–20 cm long. Fixed by a basal disk from which the sessile or slightly stiped blades develop. Blades dichotomously divided, of 4–6 mm width, linear or lobed, becoming irregular in upper parts, with rounded apices. The base of the lamina presents bundles of numerous parallel veins that diverge from the upper parts where they become anastomosed. The young parts present small veins (visible with magnifying glass). Margins are often very wavy and proliferous, sometimes with rhizoidal attachment processes or with flattened hooks (do not confound with Acrosorium uncinatum). Very polymorphic.

Figure 175. Cryptopleura ramosa. Scale on images (b,c): 1 division = 1 mm; (a) underwater photo; (b) herbarium specimen; (c) blade with veins and with wavy and proliferous margins. Reprinted from [17].

Delesseria sanguinea (Hudson) J.V. Lamouroux 1813 (Figure 176).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Sphaerococcus sanguineus (Hudson) Wahlenberg 1826.

Common name: Sea Beech.

Habitat: Marine species found on rocks in deep, shaded lower intertidal pools and in the subtidal zone.

Description: Fronds are vivid crimson and membranous, supported by a cartilaginous, cylindrical, branched stipe arising from a thickened discoid holdfast. The entire structure may reach up to 300 mm in length. Branches bear spirally arranged, leaf-like blades that are ovate-lanceolate in shape, each with a short stipe and a pinnately branched midrib. The membranous portion is monostromatic, and mature blades display undulating but intact margins. During winter, reproductive structures develop as small, oval, stalked blades along the midribs.

Figure 176. Delesseria sanguinea. Scale on image (a): 1 division = 1 mm; (a) herbarium specimen, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Erythroglossum laciniatum (Lightfoot) Maggs & Hommersand 1993 (Figure 177).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Polyneura laciniata (Lightfoot) P.S. Dixon 1983.

Common names: Laver, Laver slack, Laver sloke, Purple laver, Red Laver.

Habitat: Occurs on rocks and as an epiphyte in deep lower intertidal pools and subtidal zones down to 30 m. It is a frequent component of the Laminaria hyperborea (Phaeophyceae) understory vegetation.

Description: Fronds are crisp and rigid, with a flattened, fan-shaped morphology and a dark purplish-red coloration. When submerged, they may exhibit a striking blue iridescence. The frond shape ranges from entire to deeply cleft, dividing into wedge- or ribbon-shaped segments, and can reach up to 300 mm in length. The stipe extends up to 25 mm from a discoid base. Venation is palmate, lacking a distinct midrib, with anastomosing veins and fine microscopic veins visible in younger regions. Older portions of the frond are polystromatic, while distal areas remain monostromatic.

Figure 177. Erythroglossum laciniatum. Scale on image (b): 1 division = 1 mm; (a) underwater photo; (b) specimen detail, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Erythroglossum lusitanicum Ardré 1970 (Figure 178).

Order: Ceramiales; Family: Delesseriaceae.

Habitat: Primarily found on wave-exposed coastlines, this species thrives in the lower intertidal to upper subtidal zones, reaching depths of up to 2 m. It forms dense turfs, covering sand-laden rocks and occupying pools within these dynamic marine environments.

Description: E. lusitanicum that distinguishes it from congeners in Atlantic Europe are thallus growth that occurs in each blade by means of a single apical cell located in the tip, and its turf forming habit.

Figure 178. Erythroglossum lusitanicum. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen; (c) microscopic observation (5×). Reprinted from [17].

Grateloupia filicina (J.V. Lamouroux) C. Agardh (Figure 179).

Order: Halymeniales, Family: Grateloupiaceae.

Synonym: Delesseria filicina J.V. Lamouroux 1813.

Common name: Chop-chop.

Habitat: On rocks, on sand-covered rocks and in shallow tide pools, intertidal.

Description: Fronds compact and tufted, displaying a deep purplish-brown hue, reaching up to 120 mm in height. The main axis measures 1–4 mm in width, with a branching pattern that is either once or twice pinnate. Both axes and branchlets taper gracefully at their bases and tips.

Figure 179. Grateloupia filicina. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

Grateloupia turuturu Yamada (Figure 180).

Order: Halymeniales; Family: Grateloupiaceae.

Synonym: Halymenia sinensis C.K. Tseng & C.F. Chang 1984.

Common names: Devil’s tongue weed, Red lettuce.

Habitat: Occurs on rocks and as an epiphyte in deep lower intertidal pools and subtidal zones down to 30 m. It is a frequent component of the Laminaria hyperborea (Phaeophyceae) understory vegetation.

Description: Fronds are crisp and rigid, with a flattened, fan-shaped morphology and a dark purplish-red coloration. When submerged, they may exhibit a striking blue iridescence. The frond shape ranges from entire to deeply cleft, dividing into wedge- or ribbon-shaped segments, and can reach up to 300 mm in length. The stipe extends up to 25 mm from a discoid base. Venation is palmate, lacking a distinct midrib, with anastomosing veins and fine microscopic veins visible in younger regions. Older portions of the frond are polystromatic, while distal areas remain monostromatic.

Figure 180. Grateloupia turuturu. Scale on image (c): 1 division = 1 mm; (a) underwater photo; (b) field photo; (c) general view. Reprinted from [17].

Hypoglossum hypoglossoides (Stackhouse) Collins & Hervey (Figure 181).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Hypoglossum angustifolium (Kützing) Aysel et al. 2014.

Common name: Under tongue weed.

Habitat: On rock and epiphytic, lower intertidal and subtidal.

Description: Rose-pink to carmine fronds, membranous, 2–20 (30) cm long, arising from a discoid base. Frond linear-lanceolate, with well-marked midrib and thin membranous margins, 1–5 (8) mm wide, monostromatic except in midribs, repeatedly branched irregularly from midrib (on both sides of the midrib) in repeated branches, similar but successively shorter and narrower branches of equal shape (proliferations). Basal sections of older fronds have a stalk-like midrib. Fronds with pointed apices, margins without microscopic veins.

Figure 181. Hypoglossum hypoglossoides. Scale on images (b,c): 1 division = 1 mm; (a) field photo; (b) general view; (c) blades with mid-riband pointed apexes. Reprinted from [17].

Neopyropia leucosticta (Thuret) L.-E. Yang & J. Brodie 2020 (Figure 182).

Order: Bangiales; Family: Bangiaceae.

Synonym: Pyropia leucosticta (Thuret) Neefus & J. Brodie 2011.

Common name: Pale Patch Laver.

Habitat: Marine species, usually epiphytic on larger algae, mid-intertidal to shallow subtidal, spring to autumn, widely distributed, common.

Description: Slender, delicate reddish-brown fronds with a single-layered membranous structure, turning pink as they dry. They can reach up to 150 mm in length, emerging from a basal holdfast with a very short stipe.

Figure 182. Neopyropia leucosticta. Scale on image (b): 1 division = 1 mm, (a) field photo; (b) herbarium specimen. Reprinted from [17].

Nitophyllum punctatum (Stackhouse) Greville (Figure 183).

Order: Ceramiales; Family: Delesseriaceae.

Synonym: Aglaophyllum punctatum (Stackhouse) Kützing 1847.

Common name: Spotted scarf weed.

Habitat: On rocks, cobbles or other mobile surfaces and epiphytic, in mid- and lower intertidal pools and in the subtidal (to 15 m).

Description: Fronds are rose-pink, translucent, and delicately membranous, with an elongate, fan-shaped outline. Margins are often fringed and folded. Fronds typically reach up to 30 cm in height, though exceptional specimens may attain 50–100 cm. They are sessile or borne on a very short stipe (<2 mm long). The frond is highly polymorphic and veinless, either undivided or deeply sub-dichotomously divided to the base. Apices are blunt or rounded, often ribbon-like in appearance.

Gametophyte plants develop rounded spots up to 5 mm in diameter, appearing as swellings on both sides of the lamina. In contrast, tetrasporophyte plants produce characteristic elongated spot.

Figure 183. Nitophyllum punctatum. Scale on images (b,c): 1 division = 1 mm; (a) underwater photo; (b) tetrasporophyte (detail); (c) fructified female gametophyte (detail). Reprinted from [17].

Porphyra dioica J. Brodie & L.M. Irvine 1997 (Figure 184).

Order: Bangiales; Family: Bangiaceae.

Synonym: Porphyra umbilicalis f. rosea Hamel 1924.

Common name: Black Laver.

Habitat: Marine species, on rock, in intertidal, mainly on semi-exposed shores hanging downwards from rocks embedded in sand or affected by sand. Most common in spring and early summer; widely distributed.

Description: A delicate red alga characterized by its slender, membranous fronds with a smooth, slippery texture. Its blades resemble long, glossy ribbons and display a range of colors, from olive-green to purple-brown, sometimes appearing nearly black.

Figure 184. Porphyra dioica. (a) field photo; microscopic observation (40×) of a cross section of the blade of a female gametophyte (b), and of a male gametophyte (c) (all reprinted with permission from Ignácio Bárbara).

Porphyra linearis Greville (Figure 185).

Order: Bangiales; Family: Bangiaceae.

Synonym: Porphyra umbilicalis var. linearis (Greville) Cotton 1912.

Common names: Winter laver, Laver.

Habitat: On rocks in the upper intertidal and splash zone during winter and spring.

Description: Purple-brown, delicate, linear, membranous, 2–4 cm (−20) cm long and 0.5–1.0 (−2.5) cm broad; usually simple with short stipe from basal holdfast. Orange patches when reproductive.

Figure 185. Porphyra linearis. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) general view. Reprinted from [17].

Porphyra umbilicalis Kützing (Figure 186).

Order: Bangiales; Family: Bangiaceae.

Synonym: Porphyra insolita Kornmann & Sahling 1991.

Common names: Laverbread, Purple laver, Sloak, Slook, Laver, Tough laver.

Habitat: On rocks, mussels, etc., mid intertidal to splash zone.

Description: Reddish brown, brownish, gray brown or olive green in the field, drying to brownish purple. Circular, orbiculate to elongate frond, (up to 40 cm across, monostromatic blades single or multiple, sometimes forming a rosette. Margins are sometimes much pleated. Sori marginal, attached by a minute but stout holdfast, stipe indistinct.

Figure 186. Porphyra umbilicalis Kützing. Scale on image (b): 1 division = 1 mm, (a) field photo; (b) herbarium specimen. Reprinted from [17].

Rhodophyllis divaricata (Stackhouse) Papenfuss 1950 (Figure 187).

Order: Gigartinales; Family: Cystocloniaceae.

Synonym: Bifida divaricata Stackhouse 1809.

Common name: Leafy Rose Weed.

Habitat: This species grows on rocks, shells, and as an epiphyte in subtidal environments. It is widely distributed and commonly found.

Description: The fronds of this species are translucent, membranous, and carmine in color, dichotomously divided from the base, forming dense, globe-style tufts that can reach up to 100 mm in height. Their segments have rounded apices, lacked veins, and featured smooth margins or fringes adorned with leafy processes.

Figure 187. Rhodophyllis divaricata. (a) general view (reprinted with permission from Ignácio Bárbara); (b) Harvey’s illustration, reprinted from [18], public domain.

Rhodymenia pseudopalmata (J.V. Lamouroux) P.C. Silva 1952 (Figure 188).

Order: Rhodymeniales; Family: Rhodymeniaceae.

Synonym: Delesseria pseudopalmata (J.V. Lamouroux) J.V. Lamouroux 1813.

Common name: Rosy Fan Weed.

Habitat: his species thrives on rocks and in shady pools, extending from the lower intertidal zone to the subtidal region. It also grows epiphytically on Laminaria hyperborea stipes.

Description: This species features flattened, fan-shaped fronds with a rather stiff texture and a striking rose-red hue, reaching up to 100 mm in height. They emerge from a discoidal base, with long or short stipes. The fronds are repeatedly dichotomously lobed, characterized by wide axils, rounded apices, and smooth margins.

Figure 188. Rhodymenia pseudopalmata. Scale on image (b): 1 division = 1 mm, (a) field photo; (b) herbarium specimen. Reprinted from [17].

Schizymenia dubyi (Chauvin ex Duby) J. Agardh 1851 (Figure 189).

Order: Nemastomatales; Family: Schizymeniaceae.

Synonym: Halymenia dubyi Chauvin ex Duby 1830.

Common name: Liver Weed.

Habitat: Pools and on rock mid lower intertidal zone.

Description: The fronds of this species are erect, leaf-like, and flat, exhibiting a brown-red (liver-colored) translucency that gradually widens from the base. They may remain simple or become irregularly split or lobed at a narrow angle, often overlapping. Frequently, the fronds take on a distinct sickle shape, with smooth margins and a soft, slippery texture that does not proliferate. Cystocarps are minute and sunken, while the stipe is very short and stunted, anchored by a small discoid holdfast.

Figure 189. Schizymenia dubyi. Scale on image (b): 1 division = 1 mm, (a) field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

5.6. Calcareous Red Macroalgae

Amphiroa rigida J.V. Lamouroux 1816 (Figure 190).

Order: Corallinales; Family: Lithophyllaceae.

Synonym: Amphiroa spina Kützing 1843.

Common name: Twig algae.

Habitat: Species recorded in shallow and deep waters in sheltered and shaded sites; sometimes found on rocky pools in exposed areas. Bathymetric distribution: mainly sublittoral.

Description: A. rigida is a rigid, calcified alga characterized by its articulated, irregular, dichotomous branching, which often occurs at the edge or center of a joint. Even after drying, its joints remain firm and retain their structure. This species typically grows to a height of 2.5–6 cm and exhibits a range of pink hues, from soft pastels to vibrant tones. When dried, it transitions to a white coloration.

Figure 190. Amphiroa rigida. (a) underwater photo; (b) specimens’ detail. Reprinted from [17].

Corallina officinalis Linnaeus 1758 (Figure 191).

Order: Corallinales; Family: Corallinaceae.

Synonym: Corallina compacta P. Crouan & H. Crouan 1867.

Common name: Coral weed.

Habitat: On rocks, lower intertidal to upper subtidal; usually in intertidal pools.

Description: Fronds are whitish-pink to lilac, calcified, and articulated, typically reaching 60–70 mm in height, with occasional specimens up to 120 mm. The axis is cylindrical to compressed and repeatedly pinnate, arising from an expanded discoid base. Branching is often irregular. Growth forms are highly variable and frequently stunted. In unfavorable habitats, the erect system may be vestigial, although an extensive basal structure is often well developed.

Figure 191. Corallina officinalis. Scale = 1 cm; (a) underwater photo; (b) herbarium specimen. Reprinted from [17].

Ellisolandia elongata (J. Ellis & Solander) K.R. Hind & G.W. Saunders 2013 (Figure 192).

Order: Corallinales; Family: Corallinaceae.

Synonym: Corallina elongata J. Ellis & Solander 1786.

Habitat: On rocks, lower intertidal to upper subtidal; usually in intertidal pools.

Description: Fronds are whitish-pink to reddish-lilac, calcified, with small articulations arranged in a fish-bone-like pattern. They reach up to 5 cm in height. The axis is compressed and repeatedly pinnate, arising from a discoid base. Reproductive structures (conceptacles) appear as swollen bodies in the terminal segments, accompanied by horn-like projections and a central pore (refer to detail in Figure 192d).

Figure 192. Ellisolandia elongata. Scale on image (c): 1 division = 1 mm; (a) underwater photo; (b) field photo; (c,d) detail of the conceptacle with a pore and antennae/hornlike segments. Reprinted from [17].

Jania longifurca Zanardini 1844 (Figure 193).

Order: Corallinales; Family: Corallinaceae.

Synonym: Corallina longifurca (Zanardini) Kützing 1845.

Habitat: Growing on rocks (epilithic), frequently found in the same locations as Jania rubens, or attached to Cystoseira species and other algae as an epiphyte.

Description: The thallus is tree-like, upright, and robust, anchored by an encrusting base, with a height ranging from 3 to 7 cm. Its segmented structure is composed of genicula and intergenicula, displaying a consistent pattern of dichotomous branching. The intergenicula are cylindrical and slightly elongated, expanding at the junctions where lateral branches emerge. The conceptacles are positioned at the tips, stalked, and spherical in shape. This epiphytic species thrives from the surface down to a depth of 20 m, characterized by a soft yellowish-pink hue.

Figure 193. Jania longifurca. Scale on image (b): 1 division = 1 mm; (a) Field photo; (b) herbarium specimen. Reprinted from [17].

Jania rubens (Linnaeus) J.V. Lamouroux 1816 (Figure 194).

Order: Corallinales; Family: Corallinaceae.

Synonym: Jania spermophorus J.V. Lamouroux 1843.

Common name: Slender-beaded Coral Weed.

Habitat: Exclusively epiphytic, growing solely on the brown algae Cladostephus and Cystoseira in the lower intertidal zones of southern and western Britain and Ireland, where it is frequently abundant.

Description: Fronds are slender and rose-pink, articulated and calcified, reaching up to 50 mm in height. Branching is repeatedly dichotomous, with luxuriant specimens occasionally exhibiting secondary pinnation. Cylindrical segments measure up to 120 µm in diameter, while branch-bearing segments are slightly compressed, reaching up to 180 µm in diameter. The thallus is anchored by a small conical disk and is capable of vegetative propagation through the development of attachment disks on branches that come into contact with solid substrata.

Figure 194. Jania rubens. Scale on image (b): 1 division = 1 mm; (a) Field photo; (b) herbarium specimen, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Jania squamata (Linnaeus) Ji H. Kim, Guiry & H.-G. Choi 2007 (Figure 195).

Order: Corallinales; Family: Corallinaceae.

Synonym: Haliptilon squamatum (Linnaeus) H.W. Johansen, L.M. Irvine & A. Webster 1973.

Habitat: Marine species, mostly epiphytic on Cystoseira species in lower-shore pools on moderately wave-exposed coasts. Occasionally on rock. Rare.

Description: Fronds are distinctively pink with whitish tips, calcified, and articulated, exhibiting a regular pinnate structure that can extend up to 200 mm in length. The axis is compressed and repeatedly pinnate, emerging from and intertwining with a stoloniferous base. This species is more abundant and systematically branched compared to Corallina officinalis. The articulations are relatively large, prominently shield-shaped, and often resemble arrowheads.

Figure 195. Jania squamata. (a) Underwater photo; (b) specimen detail, reprinted from [17]; (c) Harvey’s illustration, reprinted from [18], public domain.

Lithophyllum byssoides (Lamarck) Foslie 1900 (Figure 196).

Order: Corallinales; Family: Lithophyllaceae.

Synonym: Lithophyllum lichenoides Philippi 1837.

Common names: in english: Coralline crust; in portuguese: Folha-da-pedra.

Similar species: Tenarea tortuosa (Esper) Me. Lemoine 1910 (formerly Lithophyllum tortuosum).

Habitat: Marine species, on rock, lower intertidal semi-exposed and exposed pools, frequently associated with intertidal populations of the purple sea-urchin Paracentrotus lividus, the pink encrustations.

Description: This encrusting calcareous alga forms vertical lamellae that interconnect, creating more or less regular spaces between them, a few millimeters wide. It develops extensive crusts over rocky surfaces, reaching lengths of several dozen centimeters. Living specimens, gray-violet in color, form characteristic cushion-like clumps, and it marks the lower boundary of the mid-littoral zone and can provide shelter within its cavities for a fauna assemblage with affinities to the infralittoral zone.

Figure 196. Lithophyllum byssoides. Scale on image (b): 1 division = 1 mm; (a) field photo; (b) herbarium specimen. Reprinted from [17].

Lithophyllum hibernicum Foslie 1906 (Figure 197).

Order: Corallinales; Family: Lithophyllaceae.

Synonyms: Lithophyllum fasciculatum f. subtile (Foslie) Foslie 1897; Lithothamnion fasciculatum f. subtile Foslie 1897.

Habitat: Found on rocks and other solid substrates, this species frequently thrives in wave-exposed areas of the intertidal zone.

Description: Crusts exhibit extraordinary morphological variability, ranging from smooth and tightly adhering to the substrate, to forms with thick, undulating, and bulging margins. These distinctive margins develop upon encountering a neighboring thallus, lifting the substrate in the process. The color varies from pink-violet to gray-violet. This species is similar to Lithophyllum incrustans Philippi 1837.

Figure 197. Lithophyllum hibernicum. (a) field photo, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Mesophyllum expansum (Philippi) Cabioch & M.L. Mendoza 2003 (Figure 198).

Order: Hapalidiales; Family: Hapalidiaceae.

Synonym: Lithophyllum expansum Philippi 1837.

Habitat: Calcareous encrusting species, can reach a diameter of 30 cm. Under artificial lighting, it reveals a vivid pink coloration, with elegantly draping branches. While sometimes spotted near the surface, it is well-adapted to depths of up to 70 m.

Figure 198. Mesophyllum expansum. Scale on image (b): 1 division = 1 mm; (a) general view; (b) herbarium specimen. Reprinted from [17].

Mesophyllum lichenoides (J. Ellis) Me. Lemoine 1928 (Figure 199).

Order: Hapalidiales; Family: Hapalidiaceae.

Synonym: Lithophyllum lichenoides (J. Ellis) Rosanoff ex Hauck 1883.

Common name: Pink plates.

Habitat: Marine species, epiphytic on Corallina officinalis or Ellisolandia elongata, in tidal pools; it can also occur in epilithic and epizoic forms, as well as unattached, spanning habitats from the lower intertidal zone to the subtidal region.

Description: Thin, brittle fronds, ranging from pale to dark purple, form a leafy, calcified structure. They attach at the base, with free, lobed margins. The fronds exhibit a semicircular shape with concentric banding. Reproduction occurs in winter and spring within small, wart-like conceptacles.

Figure 199. Mesophyllum lichenoides. (a) underwater photo, reprinted from [17]; (b) Harvey’s illustration, reprinted from [18], public domain.

Peyssonnelia coriacea Feldmann 1941 (Figure 200).

Order: Peyssonneliales; Family: Peyssonneliaceae.

Common names: Rumoi-iwanokawa, Mayoi-iwanokawa.

Habitat: This species is rare, typically found in the protected infralittoral and circalittoral zones, where it forms a coating on rocky surfaces shielded from intense light or settles in detrital environments with moderate water flow.

Description: This laminar alga has a slightly calcified, flat thallus with wavy margins. It attaches to the substrate via its lower surface, which bears concentric grooves along the edges. The thallus typically reaches a diameter of approximately 3 cm. Its coloration ranges from red to yellow, often displaying greenish hues, particularly near the margins or apex.

Figure 200. Peyssonnelia coriacea. (a) field photo; (b) specimen detail. Reprinted from [17].

6. Conclusions

This illustrated guide to the macroalgae of the Portuguese Atlantic continental coast stands as a valuable resource for biodiversity documentation, ecological awareness, and practical identification. By presenting a curated selection of species accompanied by visual references and updated taxonomic information, it addresses critical gaps in regional phycological literature.

The complexity of macroalgal identification, shaped by morphological plasticity, cryptic diversity, and rapid taxonomic revisions, underscores the need for dynamic and accessible tools. This guide responds by combining scientific rigor with visual clarity, facilitating accurate recognition across user groups, from researchers and students to citizens.

Importantly, the macroalgal diversity revealed along Portugal’s coast reflects both ecological richness and vulnerability. Shifts in species distributions, invasive introductions, and the ongoing impact of climate change demand vigilant monitoring and adaptive management. This guide contributes to those efforts by enabling field-based biodiversity assessments and supporting informed stewardship of coastal habitats [31,32].

As scientific understanding evolves and new species records emerge, this guide should be viewed as a living resource—open to refinement through continued fieldwork, taxonomic collaboration, and public engagement via platforms like MACOI—Portuguese Seaweeds Website (http://www.flordeutopia.pt/macoi/, accessed on 29 September 2025). Ultimately, the work encourages a deeper appreciation of marine plant life and promotes sustainable connections between coastal ecosystems and human communities.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Acknowledgments

Leonel Pereira thanks the FCT—Foundation for Science and Technology, I.P., in the structure of Project UIDB/04004/2025—Centre for Functional Ecology—Science for the People & the Planet. He would also like to thank Ignácio Bárbara, University of Coruña, for providing photos of some of the species of seaweed present on the Portuguese coast.

Conflicts of Interest

The author declares no conflicts of interest.

Glossary

Anastomosed	network of channels that separate and recombine in various points such as blood vessels or the veins of a leaf
Apex (plural: apices)	the tip or the point furthest from the point of attachment
Arbuscular	shrub-like in growth or general appearance
Axils	zone/angle of branching between the main axis and the secondary branches
Basal disk	flat structure, disk-shaped, which ensures algae fixation to the substrate
Basal	at the base, situated or attached at the base
Bifid	separated or cut in two for about half its length
Bifurcated	which is divided/branched out into two parts
Bipinnate	branching that is twice pinnate, i.e., a pinnated branch that supports itself smaller branches pinnately divided
Blade	flattened structure that normally forms the main bulk of the thallus
Bulb	rounded or globular shape
Cartilaginous	of cartilage-like consistency; firm
Cell	structural and functional unit of living beings
Conceptacles	cavities or crypts on the thallus, internally covered by reproductive structures (oogoniums and/or antheridia) and by sterile filaments (paraphyses) that communicate with the exterior through one or several pores (ostioles)
Conical	cone shaped
Coriaceous	tough as leather; like leather
Cortex/Cortication	the outermost part of the thallus, located around the central zone; is usually composed of small and pigmented cells
Corticated	provided with cortex
Corymbiform	with branches arising from different points, but reaching approximately the same height, giving the thallus a flat top appearance
Cystocarp	reproductive structure that develops on the female’s thallus of some red macroalgae, after its fertilization, and inside which are the gonimoblasts and carpospores.
Deciduous	which falls or breaks out at a certain stage of development at some point in the year
Desiccation	refers to the drying of macroalgae exposed to the dry environment when emerged from the water by the descent of the tides
Dichotomous	pattern of branching whose branches are divided into two equal branches in a regular/repeated manner
Discoid	disk-shaped
Distichous	arranged alternately in two rows along opposite sides of the axis
Distromatic	consisting of two layers of cells
Epiphyte	that grows on another plant or macroalgae
Falcate	sickle-shaped, flattened and more or less curved
Filiform	thin as a wire
Foliaceous	leaf-shaped
Frond	upright part of a macroalgae
Fusiform	spindle shape; elongated and with the extremities narrower than the center
Gametangia	Gametes-producing structure
Gametophyte	thallus where gametangia form
Gas-bladders	bladders filled with air
Helical	propeller-shaped
Hermaphrodite	that has in the same thallus female (oogonia) and male (antheridia) reproductive structures which in turn produce female gametes (oospheres) and male gametes (antherozoids)
Hook-like	resembling a hook especially in recurved form
Intertidal	coastal zone between the highest and lowest spring tide levels
Involucre	which envelops or covers
Iridescent	which reflects the colors of the rainbow, usually presenting a bluish color
Lanceolate	longer than broad, narrowly ovate, broadest in the lower half and tapering to the tip, like a lance or spear head
Lobed	central often rounded, formed by incisions to about halfway to the midrib
Margin	edge of a blade
Monostromatic	a single layer of cells
Mucilaginous	containing mucilage, viscous
Multifid	separated in many parts
Nodose	that has knots
Obtuse	not pointed, rounded
Orbiculate	sphere-shaped
Ovoid	egg-shaped
Papillae	small protrusions formed on the surface
Papyraceous	whose texture resembles papyrus
Peduncles	structures that serve as support
Perennial	permanent, who lives more than a year
Pericentrals	cells that are in the periphery of the central cell
Pinnate	branching pattern typically in pairs opposite each other, similar to a feather
Pinnule	ultimate division of the branches
Piriform	pear-shaped
Plastid	essential organelles for amino-acid synthesis, photosynthesis and other processes
Pleated	wavy
Polysiphonous	axes whose cells look like siphons
Prostrated	which grows adherent to the substrate
Pseudo-dichotomous	branched by division almost dichotomous, whose branches are divided into two unequal branches
Pyrenoid	protein granules, generally surrounded by starch; are irregularly distributed within (intra-plastidial) or outside the plastids (extra-plastidial)
Receptacles	structure with conceptacles, present in some brown algae
Rhizoids	cells or filaments that allow the thallus to be attached to the substrate
Seasonal	which only occurs at certain times of the year
Serrated	serrated; provided with small denticles
Sessile	attached directly by its base without a peduncle
Siphon	without transverse septa
Sori	group of reproductive organs on the surface of a thallus
Sparse	dispersed
Spathulate	in the form of a spatula
Stipe	portion situated between the rhizoids and the blade of a macroalgae
Stoloniferous	which forms prostrate axes (from which erect axes develop)
Subtidal	coastal zone below the level of the lowest tides
Supratidal/Splash Zone	coastal zone above the level of the highest tides
Tetrasporangia	sporangium that originates four spores
Tetrasporophyte	one of the generations of the triphasic cycle of certain red algae; produces tetrasporangia with tetraspores, that will give rise to the gametophytes
Thallus	Algal Body
Translucent	which lets the light pass and diffuses it, but does not allow a clear distinction
Trichoblasts	transparent hair-like branches, may be simple or branched
Tripinnate	branching that is twice pinnate, i.e., a pinnated branch that supports itself, smaller branches pinnately divided and where the latter also branch out in pinnated form
Truncated	cut
Tuffs	group or plume of filaments or blades
Undivided	which are not divided; whole
Uniseriate	formed by only one row of cells; can be simple or branched
Verticil	horizontal set of branches arranged around a common axis and in the same horizontal plane

References

Araújo, R.; Sousa-Pinto, I.; Bárbara, I.; Quintino, V. Macroalgal communities of intertidal rock pools in the northwest coast of Portugal. Acta Oecologica 2006, 30, 192–202. [Google Scholar] [CrossRef]
Verbruggen, H. Morphological complexity, plasticity, and species diagnosability in the application of old species names in DNA-based taxonomies. J. Phycol. 2014, 50, 26–31. [Google Scholar] [CrossRef] [PubMed]
Vasconcelos, R.P.; Reis-Santos, P.; Fonseca, V.; Maia, A.; Ruano, M.; França, S.; Vinagre, C.; Costa, M.J.; Cabral, H. Assessing anthropogenic pressures on estuarine fish nurseries along the Portuguese coast: A multi-metric index and conceptual approach. Sci. Total Environ. 2007, 374, 199–215. [Google Scholar] [CrossRef] [PubMed]
Gaspar, R.; Pereira, L.; Neto, J.M. Ecological reference conditions and quality states of marine macroalgae sensu Water Framework Directive: An example from the intertidal rocky shores of the Portuguese coastal waters. Ecol. Indic. 2012, 19, 24–38. [Google Scholar] [CrossRef]
Stewart, H.L.; Carpenter, R.C. The Effects of Morphology and Water Flow on Photosynthesis of Marine Macroalgae. Ecology 2003, 84, 2999–3012. [Google Scholar] [CrossRef]
Carpenter, R.C. Competition Among Marine Macroalgae: A Physiological Perspective. J. Phycol. 1990, 26, 6–12. [Google Scholar] [CrossRef]
Jurkus, E.; Povilanskas, R.; Taminskas, J. Current Trends and Issues in Research on Biodiversity Conservation and Tourism Sustainability. Sustainability 2022, 14, 3342. [Google Scholar] [CrossRef]
Bellgrove, A.; McKenzie, P.F.; Cameron, H.; Pocklington, J.B. Restoring rocky intertidal communities: Lessons from a benthic macroalgal ecosystem engineer. Mar. Pollut. Bull. 2017, 117, 17–27. [Google Scholar] [CrossRef] [PubMed]
Gaspar, R.; Fonseca, R.; Pereira, L. Illustrated Guide to the Macroalgae of Buarcos Bay, Figueira da Foz, Portugal; University of Coimbra: Coimbra, Portugal, 2020; 130p. [Google Scholar] [CrossRef]
Pereira, L. Guia Ilustrado das Macroalgas—Conhecer e Reconhecer Algumas Espécies da Flora Portuguesa; Coimbra University Press: Coimbra, Portugal, 2009; 90p. [Google Scholar] [CrossRef]
Bhuyan, M.; Islam, T.; Nabi, M.; Kunda, M. Pictorial Dictionary of Seaweed. 2023. Bangladesh Oceanographic Research Institute, 184p. Available online: https://www.researchgate.net/publication/378076262_Pictorial_Dictionary_of_Seaweed (accessed on 19 September 2025).
Pereira, L. Guia Ilustrado das Macroalgas Marinhas das Praias Rochosas da Figueira da Foz, Portugal/Illustrated Guide to the Marine Macroalgae of the Rocky Shores of Figueira da Foz, Portugal, 1ª Edição/Edition ed; CFE—Centre for Functional Ecology: Science for People & Planet—Marine Resources, Conservation and Technology—Marine Algae Lab: Coimbra, Portugal, 2025; in press. [Google Scholar]
Pereira, L. Non-indigenous seaweeds in the Iberian Peninsula, Macaronesia Islands (Madeira, Azores, Canary Islands) and Balearic Islands: Biodiversity, ecological impact, invasion dynamics, and potential industrial applications. Algal Res. 2024, 78, 103407. [Google Scholar] [CrossRef]
Macreadie, P.I.; Jarvis, J.; Trevathan-Tackett, S.M.; Bellgrove, A. Seagrasses and Macroalgae: Importance, Vulnerability and Impacts. In Climate Change Impacts on Fisheries and Aquaculture; John Wiley & Sons: New York, NY, USA, 2017; pp. 729–770. [Google Scholar] [CrossRef]
Yoon, H.S.; Andersen, R.A.; Boo, S.M.; Bhattacharya, D. Stramenopiles. In Encyclopedia of Microbiology, 3rd ed.; Schaechter, M., Ed.; Academic Press: Oxford, UK, 2009; pp. 721–731. [Google Scholar] [CrossRef]
Yoon, H.S.; Zuccarello, G.C.; Bhattacharya, D. Evolutionary History and Taxonomy of Red Algae. In Red Algae in the Genomic Age; Seckbach, J., Chapman, D.J., Eds.; Springer: Dordrecht, The Netherlands, 2010; pp. 25–42. [Google Scholar] [CrossRef]
Pereira, L. Portuguese Seaweeds Website. Available online: http://www.flordeutopia.pt/macoi/ (accessed on 16 August 2025).
Harvey, W.H. Phycologia Britânica; Several Volumes; Reeve & Benham: London, UK, 1851. [Google Scholar]
Pereira, L. Edible Seaweeds of the World, 1st ed.; CRC Press: Boca Raton, FL, USA, 2016; 442p, ISBN 9-781498-73047. [Google Scholar] [CrossRef]
Pereira, L. Therapeutic and Nutritional Uses of Algae. CRC Press: Boca Raton, FL, USA, 2018; 560p, ISBN 9781498755382. [Google Scholar] [CrossRef]
Leandro, A.; Pereira, L.; Gonçalves, A.M.M. Diverse Applications of Marine Macroalgae. Mar. Drugs 2020, 18, 17. [Google Scholar] [CrossRef] [PubMed]
Prisa, D.; Fresco, R.; Jamal, A.; Saeed, M.F.; Spagnuolo, D. Exploring the Potential of Macroalgae for Sustainable Crop Production in Agriculture. Life 2024, 14, 1263. [Google Scholar] [CrossRef] [PubMed]
Pereira, L. Littoral of Viana do Castelo—ALGAE (Bilingual). Câmara Municipal de Viana do Castelo: Viana do Castelo, Portugal, 2010; 68p, ISBN 978-972-588-217-7. [Google Scholar]
Pereira, L. Littoral of Viana do Castelo—ALGAE. Uses in Agriculture, Gastronomy and Food Industry (Bilingual); Câmara Municipal de Viana do Castelo: Viana do Castelo, Portugal, 2010; 68p, ISBN 978-972-588-218-4. [Google Scholar]
Kalasariya, H.S.; Yadav, V.K.; Yadav, K.K.; Tirth, V.; Algahtani, A.; Islam, S.; Gupta, N.; Jeon, B.-H. Seaweed-Based Molecules and Their Potential Biological Activities: An Eco-Sustainable Cosmetics. Molecules 2021, 26, 5313. [Google Scholar] [CrossRef] [PubMed]
Guiry, M.D. AlgaeBase (Listing the World’s Algae). National University of Ireland, Galway. Available online: https://www.algaebase.org/ (accessed on 12 September 2025).
Available online: http://www.flordeutopia.pt/macoi/spec_list_detail.php?spec_id=83&searchSpecies=gelidium+corneum+%28hudson%29+j.v.lamouroux (accessed on 20 June 2025).
Available online: https://commons.wikimedia.org/wiki/File:Ceramium_echionotum_19880601a.jpg (accessed on 20 June 2025).
Available online: https://wikidocumentaries-demo.wmcloud.org/Q55277166?language=pap (accessed on 20 June 2025).
Available online: https://pt.m.wikipedia.org/wiki/Ficheiro:Icones_of_Japanese_algae_%28Pl._CXV%29_%288006305996%29.jpg (accessed on 20 June 2025).
Gibbons, E.G.; Quijón, P.A. Macroalgal features and their influence on associated biodiversity: Implications for conservation and restoration. Front. Mar. Sci. 2023, 10, 1304000. [Google Scholar] [CrossRef]
Herrero, J.J.; Simes, D.C.; Abecasis, R.; Relvas, P.; Garel, E.; Ventura Martins, P.; Santos, R. Monitoring invasive macroalgae in southern Portugal: Drivers and citizen science contribution. Front. Environ. Sci. 2023, 11, 1324600. [Google Scholar] [CrossRef]

Figure 1. Branching types: (a) irregular; (b) opposite; (c) dichotomous; (d) whorled; (e) pectinate. Reprinted from [17]. (f) Alternate, reprinted from [18]; public domain.

Figure 2. Coastal zonation: (a)—mean high water spring tides; (b)—mean high water neap tides; (c)—mean low water neap tides; (d)—mean low water spring tides. Reprinted from [9].

Figure 3. Illustrated icons representing key aspects of macroalgae’s potential uses by humans and its relevance to non-indigenous species, adapted from [9,12].

Figure 4. Green Macroalgae (Phylum Chlorophyta). Reprinted from [17].

Figure 5. Brown Macroalgae (Phylum Heterokontophyta, Class Phaeophyceae). Reprinted from [9].

Figure 6. Red Macroalgae (Phylum Rhodophyta). Reprinted from [9].

Figure 7. Filamentous macroalgae. Reprinted from [9].

Figure 8. Foliaceus macroalgae. Reprinted from [17].

Figure 9. Tubular macroalgae. Reprinted from [9].

Figure 10. Spongy macroalgae. Reprinted from [17].

Figure 11. Filamentous macroalgae. Reprinted from [17].

Figure 12. Laminate/Foliaceus or ribbon macroalgae. Reprinted from [9].

Figure 13. Cylindrical macroalgae. Reprinted from [9].

Figure 14. Big-Sized/Laminated macroalgae (Kelps). Reprinted from [9].

Figure 15. Cylindrical/Filamentous macroalgae (1 division = 1 mm). Reprinted from [9].

Figure 16. Cylindrical/Hollow macroalgae (1 division = 1 mm). Reprinted from [9].

Figure 17. Cylindrical/Thick macroalgae (1 division = 1 mm). Reprinted from [9].

Figure 18. Flattened Thick Macroalgae (1 division = 1 mm). Reprinted from [9].

Figure 19. Thin Laminate/Foliaceus or in ribbon macroalgae (1 division = 1 mm). Reprinted from [9].

Figure 20. Calcareous macroalgae (1 division = 1 mm). Reprinted from [9].

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Pereira, L. Illustrated Guide to the Main Macroalgae of the Portuguese Continental Atlantic Coast. Encyclopedia 2025, 5, 176. https://doi.org/10.3390/encyclopedia5040176

AMA Style

Pereira L. Illustrated Guide to the Main Macroalgae of the Portuguese Continental Atlantic Coast. Encyclopedia. 2025; 5(4):176. https://doi.org/10.3390/encyclopedia5040176

Chicago/Turabian Style

Pereira, Leonel. 2025. "Illustrated Guide to the Main Macroalgae of the Portuguese Continental Atlantic Coast" Encyclopedia 5, no. 4: 176. https://doi.org/10.3390/encyclopedia5040176

APA Style

Pereira, L. (2025). Illustrated Guide to the Main Macroalgae of the Portuguese Continental Atlantic Coast. Encyclopedia, 5(4), 176. https://doi.org/10.3390/encyclopedia5040176

Article Menu

Illustrated Guide to the Main Macroalgae of the Portuguese Continental Atlantic Coast

Abstract

1. Introduction

1.1. Overview of Macroalgal Diversity and Taxonomy

1.2. Pigmentary Composition and Classification of Macroalgae

1.3. Morphological Types

Branching Types

1.4. The Habitat of Rocky Shores

1.5. Non-Indigenous Algae on the Western Portuguese Coast

1.6. Uses

2. Illustrated Guide

2.1. Green Macroalgae (Phylum Chlorophyta)

2.2. Brown Macroalgae (Phylum Heterokontophyta, Class Phaeophyceae)

2.3. Red Macroalgae (Phylum Rhodophyta)

3. Chlorophyta (Green Macroalgae)

3.1. Filamentous Green Macroalgae

3.2. Laminar Green Algae

3.3. Green Tubular and Vesiculosus Algae

3.4. Sponge Green Algae

4. Heterokontophyta, Phaeophyceae (Brown Macroalgae)

4.1. Filamentous Brown Macroalgae

4.2. Laminate/Foliaceus or Ribbons Brown Macroalage

4.3. Cylindrical Brown Macroalgae

4.4. Big-Sized, Laminated Brown Macroalgae (Kelps)

4.5. Bladder Like or Globose Algae

5. Rhodophyta (Red Macroalgae)

5.1. Cylindrical Filamentous Red Macroalgae

5.2. Cylindrical Hollow

5.3. Cylindrical Thick

5.4. Flattened Thick Red Macroalgae

5.5. Thin Laminate/Foliaceous or in Ribbons Red Macroalgae

5.6. Calcareous Red Macroalgae

6. Conclusions

Funding

Institutional Review Board Statement

Informed Consent Statement

Data Availability Statement

Acknowledgments

Conflicts of Interest

Glossary

References

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