Ovicula biradiata Manley, 2025
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https://doi.org/10.3897/phytokeys.252.137624 |
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https://doi.org/10.5281/zenodo.14889602 |
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https://treatment.plazi.org/id/A67831A0-CC0A-5090-B27A-F6936DD1B820 |
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scientific name |
Ovicula biradiata Manley |
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Ovicula biradiata Manley , gen. et. sp. nov.
Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8
Description.
Annuals, small, flowering plants usually 1–2 (– 3) cm tall, from less than 1 cm wide to 3–7 cm across, whole plants densely white-tomentose. Root single, thread-like, 0.5–1 mm wide at the plant base. Stems unbranched, erect or branches, if evident, lateral, prostrate, spreading 1–4 cm in one or more directions, internodes ca. 1 cm long. Leaves basal, mostly in tight clusters or at nodes on short stems, proximal leaves spreading, distal ascending, petioles 1–4 mm long, blades ovate, 4–7 × 2.5–5 mm, entire, planar, gently involute or nearly conduplicate. Heads heterogamous, borne singly, essentially sessile (peduncles to ca. 1 mm long), obscured by woolly leaves. Involucres 5–7 × 4–6 mm, broadly funnelform to campanulate or subglobose. Phyllaries in 3 series, ca. 1–2 in outer series, ca. 1–2 in second series, outer slightly spreading, those in outer 2 series 3–4 × 2–3 mm, ovate, inner series ca. 7, linear, ca. 2 mm wide, with scarious margins ca. 0.5 mm wide, densely white-tomentose. Receptacles ca. 1 mm across, slightly saucer-shaped to flat, sometimes with a very small conic enation from near centre, otherwise basically smooth or with faint floret scars, epaleate. Ray florets 2 (– 3) per head, 3–6 × 0.6–1 mm long, positioned on opposing sides, pistillate and fertile, strap-like; corolla tube 2–3 mm long, densely pilose distally, with wavy trichomes 0.3–1 mm long, laminae 3–6 × 0.6–1 mm, 3 - lobed, whitish, markedly 4 - nerved proximally, 6 - nerved distally, nerves maroon, proximal portion of the abaxial ray laminae densely covered with sessile or short stipitate glandular trichomes. Disc florets 10–12 per head, perfect and fertile; corolla pale yellow, ca. 2–3 mm long, tube 0.6–0.9 mm long, throat 1.6–1.8 mm long, lobes 5, 0.1–0.3 mm long, distalmost throat and lobes densely pilose with wavy trichomes 0.3–0.5 mm long; anthers yellow, distal anther appendage narrowly obovate to subsagittate; style tip appendage truncate, apex papillate. Cypselae of ray and disc florets similar, 1.5–2 mm long, obconic-obpyramidal, slightly compressed or obscurely 4–5 - angled (prismatic), ribs 4–5, densely pubescent with straight, ascending-appressed, silvery trichomes 0.5–0.9 mm long, minutely forked at tip, partially obscuring the bases of pappus scales. Pappus of ray and disc florets similar, scales 5, ca. 1–3 × 0.8–1 mm, ovate, hyaline, with an apical arista ca. 1 mm long; the scales spreading when dry (Figs 1 View Figure 1 – 7 View Figure 7 ). Chromosome number unknown.
Similar to members of tribe Helenieae (sensu Baldwin et al. (2002)) , especially Tetraneuris , with its annual habit, radiate heads, phyllaries in 3 series, convex, epaleate receptacles, ray florets pistillate and fertile, strap-like 3 - lobed ray floret laminae with prominent, coloured veins, cypselae obconical, faintly ribbed and pappus of hyaline aristate scales, disc florets perfect and fertile, corollas yellow, 5 - lobed; differs from other Helenieae genera by its smaller size, shorter stems, tightly clustered small leaves, greater tomentum density and smaller, sessile heads with only 2 (– 3) ray florets.
Type.
USA • Texas: Brewster Co.; Big Bend National Park, low gravelly limestone exposure, eroded alluvial flats, NE of Dagger Mt. ; elev. 800 m, 20 Apr 2024, Debra Manley 2, with C. Whiting, C. Hoyt, P. Manning, and S. Menzies; holotype: SRSC 00058752 About SRSC (BIBE 61799); isotype: CAS 1352777 About CAS (BIBE 61820) .
Paratypes. USA • Texas; Brewster Co.: Big Bend National Park, low gravelly limestone exposure, eroded alluvial flats, NE of Dagger Mt. ; elev. 792.5 m, 20 Apr 2024, Debra Manley 3, with C. Whiting, C. Hoyt, P. Manning, and S. Menzies; BIBE 61800 ( SRSC 00058751 About SRSC ) .
Etymology.
The generic name from Latin Ovis “ sheep ” and - cula (diminutive ending) references the dense woolly indumentum of this new plant. The name honours the desert bighorn sheep (Ovis canadensis nelsonii), an iconic, but threatened desert animal that is currently rebounding in this part of the Chihuahuan Desert, providing hope for other rare species like O. biradiata. The specific epithet biradiata references the typically two conspicuous ray florets, occasionally three per head, positioned on opposing margins of the capitulum (Figs 1 View Figure 1 , 4 View Figure 4 ). A recommended common name for O. biradiata is “ woolly devil ”, in reference to the woolly indumentum, the proximity of populations to the locality known as Devil’s Den and the tendency for the ray florets to resemble horns.
Distribution and phenology.
Ovicula biradiata is known from limestone pediments of eastern Big Bend National Park where only three small populations have been found. Within these subpopulations, individual plants were abundant, but short-lived, indicating an ephemeral life history. The species was discovered on 2 March 2024 when plants were in full flower (Fig. 1 View Figure 1 ). It is not presently known how early the plants may produce flowers, but, in the same general area, there are other species in several families that may bloom in early February or even earlier. By late May, after a period of warm and dry weather, the delicate annual plants had ceased vegetative growth and only desiccated inflorescences could be found (Fig. 4 View Figure 4 ).
Habitat and associated taxa.
The general area of the three known locations for the new taxon, as so far observed, consists of a broad floodplain composed of fine sand and clay sediments and braided with drainage. This alluvial basin terrain is fringed with low, gravel-capped pediments which then extend into foothills and steeper slopes of a flanking limestone mountain range. The locations are within 625 m of each other and occur where a shallow layer of mixed alluvial gravel and stones overlie bedrock of the Boquillas Formation. This composite substrate occurs on both the Ernst and San Vicente members of the formation and the observed habitat exposures consist of thinly-bedded limestone, carbonate shale and siltstone overlain by Quaternary gravel, which is a heterogeneous mix of surrounding geologic substrates. One site includes a significant presence of iron-bearing rocks. The known locations receive full sun throughout the day with very little shade provided by the sparse vegetation or the flat topography (Figs 3 View Figure 3 , 4 View Figure 4 ).
Widely-distributed species noted in the habitat include Vachellia vernicosa (Britton & Rose) Seigler & Ebinger , Larrea tridentata (DC.) Coville , Tiquilia greggii (Torr. & A. Gray) A. T. Richardson , T. hispidissima (Torr. & A. Gray) A. T. Richardson , Agave lechuguilla Torr. , Thymophylla acerosa (DC.) Strother , Plantago sp. L., Oenothera sp. L., Physaria sp. (Nutt.) A. Gray, Nerisyrenia camporum Greene , Krameria sp. Loefl., Bouteloua sp. Lag., Aristida sp. L., Dasyochloa pulchella (Kunth) Willd. ex Rydb. , Ariocarpus fissuratus K. Schum. , Echinocactus horizonthalonius Lem. , Opuntia sp. (L.) Mill. and Grusonia aggeria (Ralston & Hilsenb.) E. F. Anderson. Cryptobiotic soil is present in the habitat as well. See Figs 2 View Figure 2 , 3 View Figure 3 for habitat photos and Fig. 9 View Figure 9 for a distribution map.
Conservation.
Ovicula biradiata is, so far, known only from within a small area in a seldom accessed part of Big Bend National Park. Nevertheless, the extremely narrow range and ephemerality of the species suggests that it is highly sensitive to variable weather patterns. Recently, this part of the Chihuahuan Desert has been under severe drought conditions and aridity is predicted to increase in this region due to climate change ( Climate Change Response Program 2024). Under current IUCN guidelines for assessment of conservation status (IUCN Standards and Petition Committee 2022), O. biradiata would, therefore, preliminarily qualify as being vulnerable (VU) and under a high threat of extinction. More study is needed on the reproductive biology and population structure of O. biradiata , as well as potential threats to its habitat, to determine if the species should be listed by the U. S. Fish and Wildlife Service under the Federal Endangered Species Act. Due to the extreme sensitivity of the known collection sites the geocoordinates of the locality have been withheld and the locality is obscured on the map (Fig. 9 View Figure 9 ).
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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