Morphotaxonomic Assessment of the pratensis Species Complex with Ontogenetic Development and Redescription of Oligonychus pratensis (Banks) (Acari: Prostigmata: Tetranychidae)

Abstract

The Banks grass mite/New World date mite, Oligonychus pratensis (Banks) (Acari: Prostigmata: Tetranychidae), is a globally distributed and economically significant agricultural pest. The present study comprehensively addresses the morphotaxonomic identification of globally reported populations of O. pratensis, to resolve ambiguities within the pratensis complex. Detailed morphological characterizations of all mobile stages (larva, protonymph, deutonymph, male, and female) of the Californian population of O. pratensis were provided, with key diagnostic traits utilized in this taxonomic assessment. The taxonomic notes are provided for worldwide populations of O. pratensis reported from six biogeographic realms. The taxonomic identity of the claimed populations of O. pratensis from South Africa (Afrotropical realm), El Salvador (Neotropical realm), China, Pakistan (Oriental realm), and Saudi Arabia (Palearctic realm) were found to either be “doubtful” or exhibit notable differences compared to the Californian population. Notably, the purported Chinese population of O. pratensis was identified as a cryptic species, likely a novel taxon within the gossypii species subgroup. Furthermore, the study confirmed the absence of O. pratensis in Saudi Arabia. Additionally, ontogenetic changes across developmental stages are documented. The findings of this study may contribute to a clearer understanding of the true distribution and global occurrence of O. pratensis, providing robust diagnostic characteristics to support future research.

1. Introduction

The Banks grass mite/New World date mite, Oligonychus pratensis (Banks) (Acari: Prostigmata: Tetranychidae), belongs to the subgenus Reckiella Tuttle & Baker and the species group/subgroup exsiccator sensu Mushtaq et al. [1]. It is a serious pest of date fruit, grasses, maize, wheat, sorghum, and sugar cane in the New World [2,3]. It was first described in Pullman, Washington, United States (type locality) on Timothy grass (Phleum pratense L., Poaceae; type host) [4]. To date, it has been reported on approximately 83 host plants from 13 families (Arecaceae, Cucurbitaceae, Cyperaceae, Euphorbiaceae, Juglandaceae, Malvaceae, Moraceae, Poaceae, Rosaceae, Rubiaceae, Sapindaceae, Solanaceae, Zygophyllaceae) and is distributed across 17 localities in six biogeographic realms: Afrotropical, Australasian, Nearctic, Neotropical, Oriental, and Palearctic [5].

The distribution of O. pratensis in some localities (e.g., China, Egypt, Pakistan, Saudi Arabia, South Africa, and Syria) remains uncertain due to the involvement of the pratensis species complex (cryptic/sibling species) and possible taxonomic misidentification arising from observed morphological variations in male and female characteristics. Additionally, many descriptions are based on brief accounts of females and, in some cases, without male specimens [1,6,7,8,9,10,11,12,13]. The taxonomic identification of O. pratensis depends on the morphology of the male aedeagus, a feature potentially used to differentiate it from other closely related species [6,7,13,14,15,16,17]. However, the improper mounting of male specimens could jeopardize the significance of the aedeagal morphology for species differentiation [1]. This could explain the intraspecific variations in aedeagus shape detected in this and previous studies among different populations of O. pratensis described from various geographical regions [2,6,7,9,14,15,16,17,18,19,20,21].

In the original description by Banks [4], O. pratensis was briefly described solely based on female specimens, as males were unknown at the time, a fact later confirmed by McGregor [22]. In subsequent descriptions from various localities, males of O. pratensis either remained unknown (e.g., [8]), or the male slide was lost [7], or traits of the male aedeagus varied across populations [6]. In other instances, males were described briefly, sometimes without illustrating the aedeagus [10,16,19,20,23,24]. Despite exhibiting intraspecific variations, O. pratensis has been reported in some localities (e.g., [10,11,24]), without providing critical character information or making comparisons with the original or subsequent descriptions from the United States, the species’ type locality [2,4,6,17,18,22,25,26]. Moreover, it has been revealed that some purported populations of O. pratensis from China [9] and Saudi Arabia [1,10] were taxonomically misidentified [1,12,27].

Given the challenges associated with the taxonomic identification of O. pratensis, an economically significant and widely distributed spider mite pest, the objectives of this study were to (i) assess the current taxonomic status of globally reported populations of O. pratensis and (ii) provide a comprehensive morphological redescription, including its ontogenetic development, based on fresh samples from California, United States, the species’ type locality.

2. Materials and Methods

The complete taxonomic literature on O. pratensis published globally from 1912 to 2023 was compiled using various search engines, websites, acarological and entomological research journals, and personal communications with acarologists worldwide. This literature, including descriptions, illustrations, and diagnostic keys of all globally reported populations of O. pratensis e.g., [1,2,4,6,7,8,9,10,12,13,14,15,16,17,18,19,20,21,24], was critically reviewed to confirm its actual geographical distribution and discuss issues related to cryptic species within the pratensis species complex. Additionally, we contacted authors who reported O. pratensis from different countries to resolve the taxonomic identity of the pratensis complex. However, only one population of laboratory-reared O. pratensis (including all developmental stages) was kindly sent by our colleagues from California (United States) [3].

For the full morphological redescription of O. pratensis, slide-mounted larval, protonymphal, deutonymphal, and adult (male and female) specimens were examined under a BX51 phase-contrast microscope (Olympus, Tokyo, Japan) at the Acarology Research Laboratory, King Saud University (KSU), Saudi Arabia. Different body parts (including gnathosoma, idiosoma, and legs) were imaged using an auto-montage software system (Syncroscopy, Cambridge, UK) attached to a phase contrast microscope (DM2500, Leica^®, Weltzer, Germany). The captured images were used as templates and illustrated with Adobe Illustrator (Adobe System Inc., San Jose, CA, USA). The generic identification (based on females) was carried out using the diagnostic key by Bolland et al. [28]. The subgenus (based on males) and species groups/subgroups (based on females) were determined following the key of Mushtaq et al. [1], while species-level identification was conducted using the key of Mushtaq et al. [12,13]. Furthermore, the specimens of O. pratensis, reported from Riyadh, Saudi Arabia [10], were re-examined to confirm the species’ identity through female and male morphological characters. The nomenclature for leg chaetotaxy and other terminologies follows Lindquist [29], and the nomenclature for body setae follows Grandjean [30,31]. Furthermore, various traits of the male aedeagus were measured from the published illustrations in an attempt to confirm the taxonomic identity of the globally reported populations of O. pratensis [13,14,15,16,17,18]. All body measurements are provided in micrometers. The slide-mounted specimens of the received Californian population of O. pratensis were deposited in the Acarology Section of the King Saud Museum of Arthropods (KSMA), Department of Plant Protection, College of Food and Agriculture Sciences, Riyadh, Saudi Arabia.

3. Results and Discussion

• Family Tetranychidae Donnadieu.

• Subfamily Tetranychinae Berlese.

• Tribe Tetranychini Reck.

• Genus Oligonychus Berlese.

• Type species Heteronychus brevipodus Targioni-Tozzetti [32]: 255.

• Diagnosis (based on female and male). As defined by Mushtaq et al. [1].

• Subgenus Reckiella Tuttle and Baker.

• Type species Tetranychus pratensis Banks [4]: 97.

• Diagnosis (based on male). As defined by Mushtaq et al. [1].

• Oligonychus (Reckiella) pratensis (Banks [4])

• (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13, Figure 14, Figure 15, Figure 16, Figure 17, Figure 18, Figure 19, Figure 20, Figure 21 and Figure 22)

• Tetranychus pratensis Banks, 1912. Banks [4]: 97

• Paratetranychus pratensis (Banks, 1912). Banks [33]: 37

• Oligonychus pratensis (Banks, 1912). Pritchard & Baker [33]: 349; Baker & Tuttle [17]: 274;

• Oligonychus (Reckiella) pratensis (Banks, 1912). Tuttle & Baker [26]: 349; Mushtaq et al. [1]: 106.

• Known host plants. 83 host plants belonging to 13 families [5].

• Distribution. 17 localities/countries belonging to six biogeographic realms [5].

• Diagnosis (based on male and female)—Male: Aedeagus turns dorsad with distinct terminal knob having rounded anterior projection and acute posterior projection, knob with posterior projection about 1.5–1.7 times longer than anterior projection. Knob length distinctly greater than width and height of knob stem. Shaft dorsal margin about 2–2.2 times longer than shaft width and 3 times longer than knob length. Knob axis forming strong acute angle with shaft axis. Empodium I with proximoventral claws, shorter than dorsal empodial claws. Female: Tibia I with nine and tibia II with seven tactile setae; peritreme straight with a bulbous end. Opisthosoma medially with transverse striae, except longitudinal to oblique striae pattern in-between setae f1–f1, forming irregular or V-shaped pattern posterior to f1, dorsal setae slender, serrate, not set on tubercles and longer than longitudinal distances to the bases of setae next-in-line.

3.1. Complete Description of the Californian Population of O. pratensis

• Female: (Figure 1, Figure 2, Figure 3 and Figure 4; n = 5)—Length of body (v2–h2) 298–390; width (c3–c3) 240–315.

• Dorsum (Figure 1a–c): Propodosomal shield medially with longitudinal striae; opisthosoma medially with transverse striae except area in-between setae f1–f1 with distinct patch of longitudinal to oblique striae, forming irregular or V-shaped pattern posterior to f1 (Figure 1c); lateral idiosoma with longitudinal to oblique striae; dorsal striae with small, semicircular lobes, wider than long (Figure 1b); dorsal setae slender, serrate (including setae h2 and h3, finely serrated), not set on tubercles and longer than longitudinal distances to the bases of setae next-in-line (Figure 1a); setae h3 located ventrally. Lengths of dorsal setae v2 65–72, sc1 113–120, sc2 82–85, c1 97–98, c2 97–103, c3 90–102, d1 92-98, d2 98–107, e1 95–97, e2 96–97, f1 80–90, f2 82–84, h2 41–46. Distances between setal bases: v2–v2 59–67, sc1–sc1 82–89, sc2–sc2 175–213, c1–c1 69–82, d1–d1 68–87, e1–e1 81–93, f1–f1 30–39, h2–h2 31–46, c1–d1 67–74, d1–e1 46–66, e1–f1 56–61, f1–h2 65–82.

Figure 1. Oligonychus pratensis, female, dorsum. (a–c): (a), dorsum; (b), lobes; (c), stria pattern between seta f1–f1. Scale bar 100 μm.

Figure 1. Oligonychus pratensis, female, dorsum. (a–c): (a), dorsum; (b), lobes; (c), stria pattern between seta f1–f1. Scale bar 100 μm.

• Venter (Figure 2): Coxisternal area between coxae I–II and area between setae 1a–ag with transverse striae medially, small sized lobes present anterior and posterior to setae 1a, comparatively large lobes present between setae 3a–ag; lateral opisthosoma with transverse, longitudinal to oblique lobed striae, pregenital area with longitudinal striae, striae on genital flap transverse between g1–g1, oblique posteriorly; Lengths of setae 1a 40–49, 1b 57–59, 1c 59–66, 2b 57–66, 2c 73–80, 3a 41–44, 3b 51–57, 4a 53–59, 4b 56–59, ag 49–52, g1 34–38, g2 34–39, ps1 14–19, ps2 16–20, h3 41–43. Distances between setal bases: 1a–1a 28–32, 3a–3a 52–57, 4a–4a 51–52, ag–ag 77–82, g1–g1 20–25, g2–g2 82–98, ps1–ps1 20–24, ps2–ps2 16–25.

Figure 2. Oligonychus pratensis, female, venter. Scale bar 100 μm.

Figure 2. Oligonychus pratensis, female, venter. Scale bar 100 μm.

• Gnathosoma (Figure 3a,b): Ventral infracapitulum with setae m smooth, long 43–51, subequal to m–m 45–52. Palp spinneret suζ 4–4.9 long, width 3–3.3, solenidion 4–6.4 long (Figure 3a). Stylophore rounded anteriorly. Peritreme simple, straight, and oval-shaped or bulbous distally (Figure 3b).

Figure 3. Oligonychus pratensis, female gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 10 μm.

Figure 3. Oligonychus pratensis, female gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 10 μm.

• Legs (Figure 4a–d): Length of legs (excluding coxae, from trochanter to tip of claw) leg I 231–246, leg II 172–215, leg III 205–220, leg IV 242–260. Leg segment setal formula as follows: coxae 2-2-1-1; trochanters 1-1-1-1; femora 10-6-4-4; genua 5-5-4-4; tibiae 9(1φ)-7-6-7; tarsi 13(1ω+2dup)-13(1ω+1dup)-9(1ω)-9(1ω). Tarsus I with four tactile setae behind proximal duplex setae (Figure 4a), and tarsus II with three tactile setae in line with and three tactile and one solenidion behind proximal to duplex setae (Figure 4b). Empodia with three pairs of proximoventral hairs.

Figure 4. Oligonychus pratensis, female legs I–IV, (a–d); right side legs. Scale bar 100 μm.

Figure 4. Oligonychus pratensis, female legs I–IV, (a–d); right side legs. Scale bar 100 μm.

• Male: (Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9; n = 5)—Length of body (v2–h2) 245–340; width (c3–c3) 220–240.

• Dorsum (Figure 5): Propodosoma medially with longitudinal striae; opisthosoma medially and posteriorly with typical transverse striae or irregular transverse striae in-between setae f1 and f2; lateral idiosoma with longitudinal to oblique striae; all striae without lobes (Figure 5); dorsal setae slender, serrate (including setae h2 and h3, finely serrated), not set on tubercles and longer than longitudinal distances to the bases of setae next-in-line (Figure 5). Lengths of dorsal setae v2 48–56, sc1 82–90, sc2 53–68, c1 65–78, c2 59–79, c3 66–79, d1 59–69, d2 71–80, e1 52–72, e2 55–67, f1 48–53, f2 41–42, h2 26–29, h3 16–23. Distances between dorsal setae: v2–v2 48–54, sc1–sc1 66–70, sc2–sc2 152–195, c1–c1 69–72, d1–d1 64–67, e1–e1 33–39, f1–f1 25–30, h2–h2 16–18, c1–d1 51–53, d1–e1 41–46, e1–f1 28–47, f1–h2 31–32.

Figure 5. Oligonychus pratensis, male, dorsum. Scale bar 50 μm.

Figure 5. Oligonychus pratensis, male, dorsum. Scale bar 50 μm.

• Venter (Figure 6): Ventral integument medially with transverse striae, without lobes. Ventral setae smooth and thin; lengths of setae 1a 33–39, 1b 38–43, 1c 46–48, 2b 48–56, 2c 51–57, 3a 31–36, 3b 41–50, 4a 40–44, 4b 37–48, ag 39–45, g1 15–21, g2 13–20, ps1 10–13, ps2 13–15. Distances between setal bases: 1a–1a 25–27, 3a–3a 47–48, 4a–4a 41–44, ag–ag 39–40, g1–g1 12–16, g2–g2 23–31, ps1–ps1 15–20, ps2–ps2 18–24.

Figure 6. Oligonychus pratensis, male, venter. Scale bar 50 μm.

Figure 6. Oligonychus pratensis, male, venter. Scale bar 50 μm.

• Aedeagus (Figure 7; Table 1): Dorsally directed aedeagus portion with distinct terminal knob having rounded anterior and acute posterior projections. Knob with a posterior projection about 1.5–1.7 times longer than anterior projection. Knob length distinctly greater than width and height of knob stem. Shaft dorsal margin about 2–2.2 times longer than the shaft width and 3 times longer than knob length. Knob axis forming strong acute angle with shaft axis.

Figure 7. Oligonychus pratensis, male, aedeagus. Scale bar 5 μm.

Figure 7. Oligonychus pratensis, male, aedeagus. Scale bar 5 μm.

• Gnathosoma (Figure 8a,b): Ventral infracapitulum with seta m 34–36, slightly shorter than distance between m–m 38–41. Palp spinneret suζ 4–4.8 long, width 2.4–3.8, solenidion ω 4.3–5.6 long. Stylophore and peritreme similar to females.

Figure 8. Oligonychus pratensis, male gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 10 μm.

Figure 8. Oligonychus pratensis, male gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 10 μm.

• Legs (Figure 9a–d): Length of legs (excluding coxae, from trochanter to tip of claw) leg I 193–225, leg II 160–171, leg III 145–178, leg IV 195–201. Leg segment setal formula as follows: coxae 2-2-1-1; trochanters 1-1-1-1; femora 10-6-4-4; genua 5-6-4-4; tibiae 9(4φ)-7-6-7; tarsi 13(3ω+2dup)-13(1ω+1dup)-9(1ω)-9(1ω). Tarsus I with four tactile setae well-behind and two tactile in-line with proximal duplex setae (Figure 9a) and tarsus II with five tactile setae well-behind and one tactile just behind duplex setae (Figure 9b). Empodium I with two claws, a dorsal claw and a proximoventral claw (proximoventral hairs fused to form proximoventral claw, bifid distally); empodia II–IV with three pairs proximoventral hairs.

Figure 9. Oligonychus pratensis, male, (a–d), leg I and III, right side legs; leg II and IV, left side legs. Scale bar 50 μm.

Figure 9. Oligonychus pratensis, male, (a–d), leg I and III, right side legs; leg II and IV, left side legs. Scale bar 50 μm.

• Deutonymph: (Figure 10, Figure 11, Figure 12 and Figure 13; n = 5)—Length of body (v2–f2) 240–275; width (c3–c3) 200–220.

• Dorsum (Figure 10a,b): Propodosomal shield medially with longitudinal striae; opisthosoma medially with transverse striae except area in-between setae f1–f1 and f1–f2 with distinct patch of typical longitudinal, irregular longitudinal, or oblique striae (Figure 10b); lateral idiosoma with longitudinal to oblique striae; stria without lobs; dorsal setae similar to females, not set on tubercles and longer than longitudinal distances to the bases of setae next-in-line (Figure 10a); setae h2 and h3 located ventrally, finely serrated. Lengths of dorsal setae v2 54–59, sc1 97–98, sc2 52–62, c1 51–67, c2 54–72, c3 59–71, d1 71-74, d2 58–67, e1 66–74, e2 80–85, f1 61–67, f2 52–59. Distances between setal bases: v2–v2 54–57, sc1–sc1 71–74, sc2–sc2 166–175, c1–c1 67–69, d1–d1 68–75, e1–e1 51–56, f1–f1 20–28, c1–d1 43–52, d1–e1 41–44, e1–f1 43–48.

Figure 10. Oligonychus pratensis, deutonymph, dorsum. (a,b), (a), dorsum; (b), stria between seta f1–f1; Scale bar 100 μm.

Figure 10. Oligonychus pratensis, deutonymph, dorsum. (a,b), (a), dorsum; (b), stria between seta f1–f1; Scale bar 100 μm.

• Venter (Figure 11): Coxisternal area between coxae I–IV and area between setae ag–g1 with transverse striae medially, striae without lobes; lateral opisthosoma with transverse, longitudinal to oblique striae. Lengths of setae 1a 34–36, 1b 31–48, 1c 34–54, 2b 43–49, 2c 59–64, 3a 29–34, 3b 34–41, 4a 43–45, 4b 39–41, ag 38–51, g1 23–26, ps1 16–18, ps2 11–15, h2 28–33, h3 31–34. Setae g2 absent. Distances between setal bases: 1a–1a 23–25, 3a–3a 41–43, 4a–4a 43–50, ag–ag 41–44, g1–g1 28–28, ps1–ps1 11–16, ps2–ps2 12–15, h2–h2 12–18, h3–h3 48–66.

Figure 11. Oligonychus pratensis, deutonymph, venter. Scale bar 100 μm.

Figure 11. Oligonychus pratensis, deutonymph, venter. Scale bar 100 μm.

• Gnathosoma (Figure 12a,b): Ventral infracapitulum with setae m smooth, long 26–38, shorter than distance m–m 30–34. Palp spinneret suζ 4–4.7 long, width 2.4–3, solenidion ω 4.8–5 long (Figure 12a). Stylophore and peritreme similar to females (Figure 12b).

Figure 12. Oligonychus pratensis, deutonymph gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 30 μm.

Figure 12. Oligonychus pratensis, deutonymph gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 30 μm.

• Legs (Figure 13a–d): Length of legs (excluding coxae, from trochanter to tip of claw) leg I 157–171, leg II 118–132, leg III 121–126, leg IV 123–144. Leg segment setal formula as follows: coxae 2-2-1-1; trochanters 1-1-1-0; femora 6-3-2-2; genua 5-5-3-3; tibiae 7(1φ)-5-5-5; tarsi 12(1ω+2dup)-10(0+1dup)-8(1ω)-8.

Figure 13. Oligonychus pratensis, deutonymph legs, (a–d), leg I–IV, right side legs. Scale bars: 50 μm.

Figure 13. Oligonychus pratensis, deutonymph legs, (a–d), leg I–IV, right side legs. Scale bars: 50 μm.

• Protonymph: (Figure 14, Figure 15, Figure 16 and Figure 17; n = 5)—Length of body (v2–f2) 190–220; width (c3–c3) 170–183.

• Dorsum (Figure 14a,b): Propodosomal shield medially with longitudinal striae; opisthosoma medially with transverse striae except area in-between setae f1–f1 and f1–f2 with distinct patch of typical longitudinal, irregular longitudinal, or oblique striae (Figure 14b); lateral idiosoma with longitudinal to oblique striae; striae without lobes; dorsal setae similar to deutonymph, not set on tubercles, and longer than longitudinal distances to the bases of setae next-in-line; setae h2 and h3 located ventrally. Lengths of dorsal setae v2 35–43, sc1 49–66, sc2 34–46, c1 38–48, c2 41–54, c3 36–46, d1 34-46, d2 49–51, e1 33–49, e2 38–49, f1 33–48, f2 20–38. Distances between setal bases: v2–v2 45–49, sc1–sc1 60–62, sc2–sc2 131–134, c1–c1 51–56, d1–d1 52–56, e1–e1 31–33, f1–f1 21–49, c1–d1 46–51, d1–e1 33–39, e1–f1 34–44.

Figure 14. Oligonychus pratensis, protonymph dorsum. (a,b), (a), dorsum; (b), stria between seta f1–f1. Scale bar 50 μm.

Figure 14. Oligonychus pratensis, protonymph dorsum. (a,b), (a), dorsum; (b), stria between seta f1–f1. Scale bar 50 μm.

• Venter (Figure 15): Coxisternal area between coxae I–IV and area anterior and posterior to setae ag with transverse striae medially, striae without lobes; lateral opisthosoma with transverse, longitudinal to oblique striae. Lengths of setae 1a 21–25, 1b 28–33, 1c 31–37, 2b 43–45, 3a 26–38, 3b 25–31, ag 25–33, ps1 11–19, ps2 10–18, h2 20–23, h3 18–24. Setae g1 and g2 absent. Distances between setal bases: 1a–1a 18–19, 3a–3a 37–39, ag–ag 31–34, ps1–ps1 10–13, ps2–ps2 9–11, h2–h2 13–14, h3–h3 48–51.

Figure 15. Oligonychus pratensis, protonymph venter. Scale bar 50 μm.

Figure 15. Oligonychus pratensis, protonymph venter. Scale bar 50 μm.

• Gnathosoma (Figure 16a,b): Ventral infracapitulum with setae m smooth, long 28–34, shorter than distance m–m 30–32. Palp spinneret suζ 4–4 long, width 2, solenidion ω 3.2–4 long (Figure 16a). Stylophore and peritreme similar to females (Figure 16b).

Figure 16. Oligonychus pratensis, protonymph gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 20 μm.

Figure 16. Oligonychus pratensis, protonymph gnathosoma: (a,b); (a), palp; (b), stylophore, scale bar 20 μm.

• Legs (Figure 17a–d): Length of legs (excluding coxae, from trochanter to tip of claw) leg I 121–128, leg II 98–110, leg III 97–103, leg IV 84–100. Leg segment setal formula as follows: coxae 2-1-1-0; trochanters 0-0-0-0; femora 3-3-2-2; genua 4-4-2-2; tibiae 5(1φ)-5-5-5; tarsi 9(0ω+2dup)-9(0ω+1dup)-8-6.

Figure 17. Oligonychus pratensis, protonymph legs: leg I–IV; (a–d), right side legs. Scale bars: 50 μm.

Figure 17. Oligonychus pratensis, protonymph legs: leg I–IV; (a–d), right side legs. Scale bars: 50 μm.

• Larva: (Figure 18, Figure 19, Figure 20 and Figure 21; n = 5)—Length of body (v2–f2) 165–190; width (c3–c3) 125–140.

• Dorsum (Figure 18): Propodosomal shield medially with longitudinal to oblique striae; opisthosoma medially with transverse striae; lateral idiosoma with longitudinal to oblique striae; striae without lobes; dorsal setae similar to deutonymph, not set on tubercles, and longer than longitudinal distances to the bases of setae next-in-line; setae h2 and h3 located ventrally. Lengths of dorsal setae v2 37–48, sc1 56–59, sc2 44–49, c1 41–49, c2 38–44, c3 38–47, d1 37–41, d2 36–43, e1 34–44, e2 35–44, f1 34–41, f2 35–36. Distances between setal bases: v2–v2 37–46, sc1–sc1 56–59, sc2–sc2 88–94, c1–c1 39–49, d1–d1 41–48, e1–e1 26–27, f1–f1 11–15, c1–d1 44–47, d1–e1 29–38, e1–f1 36–43.

Figure 18. Oligonychus pratensis, larva dorsum. Scale bar 50 μm.

Figure 18. Oligonychus pratensis, larva dorsum. Scale bar 50 μm.

• Venter (Figure 19): Coxisternal area between coxae I–III and area posterior to setae 3a with transverse striae medially, striae without lobes; lateral opisthosoma with longitudinal to oblique striae. Lengths of setae 1a 23–25, 1b 29–32, 3a 23–25, ps1 9–11, ps2 11–13, h2 19–25, h3 18–22. Setae ag, g1, and g2 absent. Distances between setal bases: 1a–1a 21–22, 3a–3a 40–48, ps1–ps1 8–11, ps2–ps2 8–11, h2–h2 8–12, h3–h3 24–37.

Figure 19. Oligonychus pratensis, larva venter. Scale bar 50 μm.

Figure 19. Oligonychus pratensis, larva venter. Scale bar 50 μm.

• Gnathosoma (Figure 20a,b): Palp spinneret suζ 3.2–4.1 long, width 1.3, solenidion ω 3–3.8 long (Figure 20a). Stylophore and peritreme similar to females (Figure 20b).

Figure 20. Oligonychus pratensis, larva gnathosoma; (a,b), (a) palp; (b) stylophore. Scale bar 20 μm.

Figure 20. Oligonychus pratensis, larva gnathosoma; (a,b), (a) palp; (b) stylophore. Scale bar 20 μm.

• Legs (Figure 21a–c): Length of legs (excluding coxae, from trochanter to tip of claw) leg I 109–118, leg II 91–103, leg III 97–107. Leg segment setal formula as follows: coxae 1-0-0; trochanters 0-0-0; femora 3-3-2; genua 4-4-2; tibiae 5(1φ)-5-5; tarsi 7(0ω+1dup)-7(0ω+1dup)-6. Tarsus I and tarsus II with two tactile seta proximal to duplex setae. Empodia with three pairs of proximoventral hairs.

Figure 21. Oligonychus pratensis, larva legs: leg I–III, (a–c); right side legs. Scale bar 50 μm.

Figure 21. Oligonychus pratensis, larva legs: leg I–III, (a–c); right side legs. Scale bar 50 μm.

3.2. Remarks

The complete morphological description of all developmental stages of O. pratensis (Californian population) is hereby provided for the first time (Table 2). The ontogenetic studies of the tetranychid mites are very rare, and it becomes difficult to provide useful information related to setal pattern differences. Li et al. [9] incorrectly provided the ontogeny of O. pratensis due to wrong species identification. It will be discussed in detail in later sections and will be referred to as “pratensis sensu Li et al.” for comparison in this section.

The basic chaetotaxy pattern in tetranychid mites was studied by Grandjean [34] and updated by Lindquist [29]. It was reported that the full extent of coxal setae appears at the deutonymphal and adult stages and that the absence or presence of setae on coxae IV could potentially differentiate between protonymph and deutonymph stages [29]. A similar pattern was observed in the Californian population of O. pratensis, where the coxae IV setae (4b) appear in the deutonymphal stage while they were absent in the protonymph (Table 2).

The setae on the leg trochanters of Californian O. pratensis followed the typical pattern of the family Tetranychidae [29], where trochanters I–III had one setae (v’) first appearing at deutonymphal stages and on trochanter IV only at the adult stage. Typically for the family Tetranychidae [29], femurs I–III of O. pratensis larvae in the present study have a 3-3-2 setal formula. This continued to appear in protonymph with formula 3-3-2-2. At the deutonymphal stage, three more setae were added to femur I, while none were added to femur II–IV. The complete set of femoral setae appeared in adult stages (Table 2). The chaetotaxy of leg genu, tibiae, and tarsi I–IV also followed the typical pattern of the subfamily Tetranychinae [29]. However, setae v1’ were added in female tarsus II, differentiating Californian O. pratensis from pratensis sensu Li et al. [9].

3.3. Taxonomic Notes on the Globally Reported Population of O. pratensis

3.3.1. Notes on the Afrotropical Populations of O. pratensis

Oligonychus pratensis has been reported in the Afrotropical realm in four countries: Mauritius, Madagascar, Senegal, and South Africa [5,14,23,35,36]. The populations from Mauritius [35], Madagascar [36], and Senegal [23] were not described morphotaxonomically. However, brief morphological data were provided for the South African population [14], but its taxonomic identity was later questioned and deemed ‘doubtful’ as slide-mounted male specimens were lost [7]. Based on the limited morphological data from Meyer and Ryke [14] and through the available/published diagnostic keys [1,13], the South African O. pratensis [14] belongs to the species group/subgroup exsiccator [1]. However, it differs from the Californian population of O. pratensis in several features: females possess three tactile setae behind the proximal duplex setae (vs. four in the Californian population), and there are notable variations (or differences) in aedeagal traits (Table 1; Figure 22). For example, the shaft’s dorsal margin is approximately 2.3 times longer than the knob length (vs. 3 times); the knob is about 2.3 times longer than its stem width (vs. more than 3 times); the knob’s posterior projection is shorter than the stem height (vs. longer); and the angle between the shaft and the bent terminal part is obtuse (vs. acute in the Californian population). We recommend a comprehensive revision using integrative taxonomic approaches to confirm the distribution of O. pratensis in the Afrotropical realm, including recollection from previously reported localities and host plants.

Table 1. Morphometric data of different aedeagal parameters—viz. height of bent aedeagal part (H1), height of knob stem (H2), length of shaft dorsal margin (L1), length of knob (L2), width of shaft (W1), width of knob stem (W2), length of knob anterior projection (AL), length of knob posterior projection (PL), angle formed between shaft axis and knob axis (α1), and angle formed between shaft axis and axis of bent part (α2), relatively measured for different populations of O. pratensis, either collected/described in the present study or re-described from the published literature.

O. pratensis Populations (References)	H1/L1	H1/W1	L1/L2	L1/W1	L2/W2	L2/H2	PL/AL	PL/H2	PL/W2	α1	α2
O. pratensis (California, present study)	0.3	0.6	3.0	2.0	3.3	2.7	1.5	1.2	1.5	22.0	69.0
A-a [18]	0.3	0.6	3.5	1.9	3.0	3.0	0.7	1.0	1.0	29.0	73.0
A-b [18]	0.4	0.8	3.4	2.0	3.5	2.0	2.8	1.0	1.8	30.0	74.0
B [6]	0.6	1.0	2.0	1.7	2.5	2.5	2.8	0.9	0.9	25.0	86.0
C [14]	0.3	0.6	2.3	1.6	2.3	3.5	1.3	0.6	0.4	9.0	113.0
D [19]	0.6	1.0	2.1	1.6	2.9	1.8	1.2	0.6	1.0	24.0	75.0
E [20]	0.7	0.9	1.8	1.3	2.8	1.7	2.8	0.8	1.3	17.0	80.0
F [37]	0.4	0.6	3.2	1.7	2.6	1.8	2.1	0.8	1.1	21.0	68.0
G [7]	0.4	0.5	3.5	1.4	1.9	2.6	0.8	0.6	0.4	27.0	73.0
H [15]	0.3	0.5	3.6	1.4	1.7	1.7	2.5	0.9	0.9	18.0	70.0
I [6]	0.5	0.6	2.6	1.3	2.6	1.7	1.0	0.5	0.8	30.0	72.0
J [16]	0.7	0.7	1.8	1.0	2.5	1.5	1.6	0.5	0.8	parallel	83.0
K [17]	0.5	0.8	2.8	1.7	3.4	1.7	1.2	0.6	1.2	36.0	72.0
L-a [21]	0.5	0.8	2.8	1.6	2.0	1.9	1.2	0.6	0.7	45.0	70.0
L-b [21]	0.4	0.6	2.7	1.4	2.3	2.6	1.4	0.9	0.8	40.0	73.0
L-c [21]	0.4	0.5	2.9	1.3	3.0	2.5	0.7	0.7	0.8	25.0	78.0
M-a [9]	0.5	1.0	3.1	2.3	2.8	1.7	1.5	0.6	1.0	31.0	66.0
M-b [9]	0.4	1.0	2.9	2.3	2.8	1.9	1.2	0.7	1.0	33.0	74.0

H1/L1, The height of the bent aedeagal part (H1) divided by the length of the shaft dorsal margin (L1). H1/W1, The height of the bent aedeagal part (H1) divided by the shaft width (W1). L1/L2, The length of the shaft dorsal margin (L1) divided by the knob length (L2). L1/W1, The length of the shaft dorsal margin (L1) divided by the shaft width (W1). L2/W2, The length of the knob (L2) divided by the width of the knob stem (W2). L2/H2, The length of the knob (L2) divided by the height of the knob stem (H2). PL/AL, The length of the knob posterior projection (PL) divided by the length of the knob anterior projection (AL). PL/H2, The length of the knob posterior projection (PL) divided by the height of the knob stem (H2). PL/W2, The length of the knob posterior projection (PL) divided by the width of the knob stem (W2).

Table 1. Morphometric data of different aedeagal parameters—viz. height of bent aedeagal part (H1), height of knob stem (H2), length of shaft dorsal margin (L1), length of knob (L2), width of shaft (W1), width of knob stem (W2), length of knob anterior projection (AL), length of knob posterior projection (PL), angle formed between shaft axis and knob axis (α1), and angle formed between shaft axis and axis of bent part (α2), relatively measured for different populations of O. pratensis, either collected/described in the present study or re-described from the published literature.

O. pratensis Populations (References)	H1/L1	H1/W1	L1/L2	L1/W1	L2/W2	L2/H2	PL/AL	PL/H2	PL/W2	α1	α2
O. pratensis (California, present study)	0.3	0.6	3.0	2.0	3.3	2.7	1.5	1.2	1.5	22.0	69.0
A-a [18]	0.3	0.6	3.5	1.9	3.0	3.0	0.7	1.0	1.0	29.0	73.0
A-b [18]	0.4	0.8	3.4	2.0	3.5	2.0	2.8	1.0	1.8	30.0	74.0
B [6]	0.6	1.0	2.0	1.7	2.5	2.5	2.8	0.9	0.9	25.0	86.0
C [14]	0.3	0.6	2.3	1.6	2.3	3.5	1.3	0.6	0.4	9.0	113.0
D [19]	0.6	1.0	2.1	1.6	2.9	1.8	1.2	0.6	1.0	24.0	75.0
E [20]	0.7	0.9	1.8	1.3	2.8	1.7	2.8	0.8	1.3	17.0	80.0
F [37]	0.4	0.6	3.2	1.7	2.6	1.8	2.1	0.8	1.1	21.0	68.0
G [7]	0.4	0.5	3.5	1.4	1.9	2.6	0.8	0.6	0.4	27.0	73.0
H [15]	0.3	0.5	3.6	1.4	1.7	1.7	2.5	0.9	0.9	18.0	70.0
I [6]	0.5	0.6	2.6	1.3	2.6	1.7	1.0	0.5	0.8	30.0	72.0
J [16]	0.7	0.7	1.8	1.0	2.5	1.5	1.6	0.5	0.8	parallel	83.0
K [17]	0.5	0.8	2.8	1.7	3.4	1.7	1.2	0.6	1.2	36.0	72.0
L-a [21]	0.5	0.8	2.8	1.6	2.0	1.9	1.2	0.6	0.7	45.0	70.0
L-b [21]	0.4	0.6	2.7	1.4	2.3	2.6	1.4	0.9	0.8	40.0	73.0
L-c [21]	0.4	0.5	2.9	1.3	3.0	2.5	0.7	0.7	0.8	25.0	78.0
M-a [9]	0.5	1.0	3.1	2.3	2.8	1.7	1.5	0.6	1.0	31.0	66.0
M-b [9]	0.4	1.0	2.9	2.3	2.8	1.9	1.2	0.7	1.0	33.0	74.0

H1/L1, The height of the bent aedeagal part (H1) divided by the length of the shaft dorsal margin (L1). H1/W1, The height of the bent aedeagal part (H1) divided by the shaft width (W1). L1/L2, The length of the shaft dorsal margin (L1) divided by the knob length (L2). L1/W1, The length of the shaft dorsal margin (L1) divided by the shaft width (W1). L2/W2, The length of the knob (L2) divided by the width of the knob stem (W2). L2/H2, The length of the knob (L2) divided by the height of the knob stem (H2). PL/AL, The length of the knob posterior projection (PL) divided by the length of the knob anterior projection (AL). PL/H2, The length of the knob posterior projection (PL) divided by the height of the knob stem (H2). PL/W2, The length of the knob posterior projection (PL) divided by the width of the knob stem (W2).

Table 2. Ontogenetic development of the chaetotaxy of legs in Oligonychus pratensis (Banks) (Acari: Prostigmata: Tetranychidae).

Leg	Stage	Coxa	Trochanter	Femur	Genu	Tibia	Tarsus
I	Larvae	1b	-	d, v’, bv”	l’, v’, l” v”	db, l’, v’, l”, v”, φ	pζ’, u’, ft’, pζ”, u”, ft”, pv’ pv” ω”
	Protonymph	1c	-	-	-	-	tc’, tc’’, ω’, v’1
	Deutonymph	-	v’	l’, l”, v”	d	l’1, l”1	ω’’1, v’’, l’1, l”1
	Female	-	-	l’1, l”1, v’1, v”1	-	v’1, v”1	v’2
	Male	-	-	l’1, l”1, v’1, v”1	-	φ’1, φ”1, φ”2	ω’1, ω’2
II	Larvae	-	-	d, v’, bv”	l’, v’, l”, v”	db, l’, v’, l”, v”	pζ’, u’, ft’, pζ”, u”, ft”, pv’ pv” ω”
	Protonymph	2b	-	-	-	-	tc’, tc’’
	Deutonymph	2c	v’	-	d	-	-
	Female	-	-	l’1, l”1, v’’1	-	l’1, v’1-	-
	Male	-	-	_	-	-	-
III	Larvae	-	-	ev’, d	l’, v’	d, l’, v’, l”, v”	u’, u”, ft’, ft”, pv’ pv”
	Protonymph	3b	-	-	-	-	tc’, tc’’
	Deutonymph	-	v’	-	d	-	ω’
	Female	-	-	v’, l’1	v”	v”1	v’1
	Male	-	-	-	v”	-	-
IV	Protonymph	-	-	d, ev’	l’, v’	d, l’, v’, l”, v”	u’, u”, ft’, ft”, pv’ pv”
	Deutonymph	4b	-	-	d	-	tc’, tc’’
	Female	-	v’	v’, l’1	v”	l’1, v’1	ω’, v’1
	Male	-	-	-	-	-	-

Table 2. Ontogenetic development of the chaetotaxy of legs in Oligonychus pratensis (Banks) (Acari: Prostigmata: Tetranychidae).

Leg	Stage	Coxa	Trochanter	Femur	Genu	Tibia	Tarsus
I	Larvae	1b	-	d, v’, bv”	l’, v’, l” v”	db, l’, v’, l”, v”, φ	pζ’, u’, ft’, pζ”, u”, ft”, pv’ pv” ω”
	Protonymph	1c	-	-	-	-	tc’, tc’’, ω’, v’1
	Deutonymph	-	v’	l’, l”, v”	d	l’1, l”1	ω’’1, v’’, l’1, l”1
	Female	-	-	l’1, l”1, v’1, v”1	-	v’1, v”1	v’2
	Male	-	-	l’1, l”1, v’1, v”1	-	φ’1, φ”1, φ”2	ω’1, ω’2
II	Larvae	-	-	d, v’, bv”	l’, v’, l”, v”	db, l’, v’, l”, v”	pζ’, u’, ft’, pζ”, u”, ft”, pv’ pv” ω”
	Protonymph	2b	-	-	-	-	tc’, tc’’
	Deutonymph	2c	v’	-	d	-	-
	Female	-	-	l’1, l”1, v’’1	-	l’1, v’1-	-
	Male	-	-	_	-	-	-
III	Larvae	-	-	ev’, d	l’, v’	d, l’, v’, l”, v”	u’, u”, ft’, ft”, pv’ pv”
	Protonymph	3b	-	-	-	-	tc’, tc’’
	Deutonymph	-	v’	-	d	-	ω’
	Female	-	-	v’, l’1	v”	v”1	v’1
	Male	-	-	-	v”	-	-
IV	Protonymph	-	-	d, ev’	l’, v’	d, l’, v’, l”, v”	u’, u”, ft’, ft”, pv’ pv”
	Deutonymph	4b	-	-	d	-	tc’, tc’’
	Female	-	v’	v’, l’1	v”	l’1, v’1	ω’, v’1
	Male	-	-	-	-	-	-

Figure 22. Different aedeagus shapes of O. pratensis showing variations, redrawn from previous descriptions, (A-a,A-b) [18], (B) [6] (C) [14], (D) [19], (E) [20], (F) [37], (G) [7], (H) [15], (I) [6], (J) [16], (K) [17], (L-a–L-c) [21], and, (M-a,M-b) [9]. Scale bar 10μm.

Figure 22. Different aedeagus shapes of O. pratensis showing variations, redrawn from previous descriptions, (A-a,A-b) [18], (B) [6] (C) [14], (D) [19], (E) [20], (F) [37], (G) [7], (H) [15], (I) [6], (J) [16], (K) [17], (L-a–L-c) [21], and, (M-a,M-b) [9]. Scale bar 10μm.

3.3.2. Notes on the Australasian Populations of O. pratensis

In the Australasian realm, O. pratensis has been reported only from the Hawaiian Islands [5,6,35]. The specimens of the Hawaiian population were initially misidentified/mislabeled as O. exsiccator (Zehnter) at the Acarology Laboratory, University of Hawaii at Manoa, as noted by Jeppson et al. [6]. Later, Goff [38] reexamined these specimens and confirmed them as O. pratensis but did not describe them morphotaxonomically. We recommend a thorough investigation of the Hawaiian population of O. pratensis by revisiting and recollecting the fresh specimens from the reported localities and host plants.

3.3.3. Notes on the Nearctic Populations of O. pratensis

In the Nearctic realm, O. pratensis has been reported by various authors from Mexico and the United States (the country of its type locality) [5]. However, only a few authors have provided taxonomic descriptions (e.g., [2,4,6,16,17,18,20,22,26]), offering morphological details of only the key traits of the male aedeagus. Pritchard and Baker [6] briefly described the male of O. pratensis, collected from the type locality (Pullman, WA, USA), and designated it as a topotype. Further, the intraspecific variations in aedeagal morphology among different Nearctic populations of O. pratensis were highlighted. Additionally, the aedeagal parameters of some previously described Nearctic populations [2,16,17,20] differed from those of the Californian population examined in this study (Table 1; Figure 22).

3.3.4. Notes on the Neotropical Populations of O. pratensis

In the Neotropical realm, O. pratensis has been reported from five countries: Brazil, Colombia, Costa Rica, El Salvador, and Honduras [5]. However, most of these reports (e.g., [39,40,41,42]) lack detailed morphotaxonomic information, and only brief morphological data for the population in El Salvador were provided [19]. We observed morphological variations/differences in key traits of the male aedeagus between the populations from El Salvador and California (Table 1; Figure 22). Additionally, Feres et al. [42] reported O. pratensis inhabiting the desert fan palm, Washingtonia filifera (Lindl.) H.Wendl. (Arecaceae), in Brazil, without morphological description or illustration. Globally, W. filifera has not been reported as a host for O. pratensis [5], except for a misidentification of O. washingtoniae as O. pratensis in Saudi Arabia [1,27]. Recently, O. washingtoniae has also been reported in Iran, inhabiting the same host plant [43], which raises doubts about identifying O. pratensis reported by Feres et al. [42].

3.3.5. Notes on the Oriental Populations of O. pratensis

In the Oriental (Indomalayan) realm, O. pratensis has been reported from two countries: China and Pakistan [5]. In China, O. pratensis was reported on grasses (Poaceae) in Jiangxi Province by Ma and Yuan [44] and in Hunan Province by Li et al. [9]. However, Ma and Yuan [44] did not provide morphological details for the Jiangxi population, whereas Li et al. [9] provided a full morphological description and ontogenetic development for the Hunan population. The taxonomic identity of the claimed Hunan population of O. pratensis [9] was later revealed as a cryptic species belonging to the species subgroup gossypii of the species group exsiccator [1]. Within the gossypii subgroup (10 species), the Hunan population closely resembles O. uruma [45], as both share key morphological traits of the male aedeagus, female and male palp spinneret, female medial dorsal hysterosomal striae, and number of setae on tibia I. However, the claimed Chinese population of O. pratensis differs from O. uruma by having a female peritreme straight distally (vs. hooked), female tarsus III and IV with eight and nine tactile setae, respectively (vs. 9 and 10), and a male aedeagus with a shaft dorsal margin almost three times longer than the knob (vs. less than 2.5 times longer in O. uruma). The present study reveals that the purported Chinese population of O. pratensis [9] is probably a ‘new species’ in the genus Oligonychus.

From Pakistan, O. pratensis has been reported, first and only time on Abelmoschus esculentus (L.) Moench (Malvaceae), Morus alba L. (Moraceae), and Solanum melongena L. (Solanaceae) [8,46]. The Pakistani populations were either briefly described based on a single female specimen [46], or without any morphological details [46]. We found that the females of Pakistani O. pratensis [8] exhibited notable differences, such as having eight setae on femur I and seven setae on tibia III vs. 10 and six, respectively, in the Californian population of O. pratensis.

3.3.6. Notes on the Palearctic Populations of O. pratensis

In the Palearctic realm, O. pratensis has been reported in five countries: Algeria, Egypt, Iraq, Saudi Arabia, and Syria [5]. Unfortunately, no morphological details were provided for any of these reported populations. Despite our efforts to obtain specimens from some Palearctic populations for morphological comparisons, including attempts with colleagues (e.g., [11]), we were unsuccessful. In Saudi Arabia (SA), O. pratensis has been reported on Zea mays L., Cynodon dactylon L. (Poaceae), and W. filifera [1,10,47], but without morphological details. Subsequent studies have since corrected this misidentification of two Saudi populations of O. pratensis. The identity of the O. pratensis population reported from Riyadh (SA) was confirmed as O. washingtoniae [1,27], while another from Baha was reidentified as O. afrasiaticus (McGregor) [10,13]. In this study, the third reported O. pratensis population, collected from Riyadh in 2010/2014 [10], was re-examined and confirmed as O. afrasiaticus. Furthermore, an integrated taxonomic investigation of Oligonychus species diversity in SA did not report O. pratensis [48], suggesting its absence in the region. These findings encourage revisiting, re-collecting, and re-examining the O. pratensis populations reported in Algeria, Iraq, Egypt, and Syria to confirm the species’ identity.

4. Conclusions

In conclusion, the present study comprehensively discussed the taxonomic challenges associated with the Oligonychus pratensis species complex, based on the globally published literature and the detailed morphological characterization of the Californian population of O. pratensis. Several populations previously identified as O. pratensis from South Africa (Afrotropical realm), El Salvador (Neotropical realm), China, Pakistan (Oriental realm), and Saudi Arabia (Palearctic realm) were determined to be either ‘doubtful’ or ‘misidentified.’ Furthermore, populations briefly described in localities such as Algeria, Brazil, Egypt, Iraq, and Syria warrant comprehensive re-examination. This should involve re-collecting specimens from the reported localities and employing modern integrated taxonomic approaches. Additionally, the morphological analysis conducted in this study suggests that the O. pratensis population reported in China may represent a novel species within the genus Oligonychus (Reckiella), specifically belonging to the gossypii subgroup of the exsiccator species group sensu Mushtaq et al. Moreover, it was revealed that O. pratensis does not occur in Saudi Arabia and that prior records of this species from the region likely resulted from morphological misidentification. The current morphological and previously conducted molecular characterization (GenBank accession number: OQ185450) [13] of the Californian population of O. pratensis can serve as a guideline for confirming the taxonomic identity of any closely related populations/species within the pratensis complex.