*2.2. Morphological Observations*

Morphological characters were evaluated according to the List of Descriptors for *Origanum vulgare* L. elaborated by the Medicinal and Aromatic Plants Working Group of European Cooperative Programme for Plant Genetic Resources (MAPs WG ECP/GR) [40]. Observations were carried out directly before the first harvest of raw material, on 10 plants per subspecies. Following traits were determined: plant growth habit, plant height (cm), number of shoots per plant, number of internodes per shoots, color of petals, branching density, stem pubescence, color of stem, degree of lignification, foliage density, shape of leaf blade, leaf area, leaf margin and shape of leaf apex. Moreover, microscopic observations concerning density of glandular trichomes on abaxial and adaxial surface of the leaves were evaluated, according to the method described by Kosakowska et al. [41]. Photographic documentation was performed (Figures 1 and 2).

(**a**) (**b**)

(**a**) (**b**) **Figure 2.** Glandular trichomes on abaxial leaf surface of common oregano (**a**) and Greek oregano (**b**).

#### *2.3. Chemical Analysis*

#### 2.3.1. Content of Essential Oil

A total of 50 g of air-dried herb was subjected for hydrodistillation for 3 h using a Clevenger-type apparatus. The content of essential oil was expressed as g <sup>×</sup> 100 g−<sup>1</sup> of dry weight (DW). Essential oils were collected and stored in amber vials, at 4 ◦C.

2.3.2. Analysis of Essential Oils by GC-MS and GC-FID (Gas Chromatography Coupled with Mass Spectrometry and Flame Ionization Detector)

The analysis was carried out by usage of an Agilent Technologies 7890A gas chromatograph coupled with a flame ionization detector (FID) and MS Agilent Technologies 5975C Inert XL\_MSD with Triple Axis Detector (Agilent Technologies, Wilmington, DE, USA). Polar, capillary, HP 20M column (25 m × 0.32 mm × 0.3 μm film thickness) (Agilent Technologies, Wilmington, DE, USA) was used. Separation conditions were given previously by B ˛aczek et al. [42].

#### 2.3.3. Total Content of Phenolic Acids

The analyses (Arnov's method) was performed in accordance with Polish Pharmacopeia 6th ed. [43]. A total of 1 g of air-dry, grounded herb was extracted twice with portions of 25 mL of distilled water (a total of 50 mL), with shaking for 30 min each time at room temperature (a total of 1 h). Collected extract was filled to 50 mL with distilled water. A total of 1 mL of extract was mixed with 5 mL of distilled water, 1 mL 0.5 M HCl, 1 mL of Arnov reagent (10 g of sodium molybdate and 10 g of sodium

nitrite dissolved in 100 mL of distilled water) and 1 mL 1 M NaOH and subsequently completed to 10 mL with distilled water. The absorbance of both basic (with extract) and comparison (without extract) solutions were measured at 490 nm. The total phenolic acid content was recalculated and given as caffeic acid equivalent (g <sup>×</sup> 100 g−<sup>1</sup> DW).
