Boechera oxylobula |
Boechera pusilla |
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Habit | Perennials; short- to long-lived; (cespitose); sexual; caudex usually not woody. | Perennials; long-lived; (cespitose); apomictic; caudex often woody. |
Stems | usually 3–7 per caudex branch, arising from margin of rosette near ground surface, or arising laterally proximal to sterile shoots, 0.4–2.5 dm, glabrous or pubescent proximally, trichomes simple and short-stalked, 2-rayed, 0.1–0.4 mm, glabrous distally. |
usually 2–6 per caudex branch, arising from margin of rosette near ground surface, 0.5–2 dm, glabrous or sparsely pubescent proximally, trichomes simple and short-stalked, 2-rayed, to 0.2 mm, glabrous distally. |
Basal leaves | blade linear to linear-oblanceolate, 1–2.5 mm wide, margins usually entire, rarely denticulate, often ciliate, trichomes (simple), 0.3–0.7 mm, surfaces glabrous or sparsely pubescent, trichomes short-stalked, 2- or 3-rayed, 0.1–0.4 mm. |
blade linear-oblanceolate, 1–2.5 mm wide, margins entire, ciliate along petiole, trichomes (simple), 0.4–0.7 mm, surfaces usually sparsely pubescent, rarely glabrous, trichomes short-stalked, 2- or 3-rayed, 0.1–0.4 mm. |
Cauline leaves | 3–12, not concealing stem; blade auricles absent, surfaces of distalmost leaves usually glabrous, rarely sparsely pubescent. |
3–5, not concealing stem; blade auricles 0–0.2 mm, surfaces of distalmost leaves usually glabrous or, rarely, margins sparsely ciliate. |
Racemes | 2–12-flowered, unbranched. |
6–13-flowered, unbranched. |
Flowers | ascending-divaricate at anthesis; sepals glabrous or pubescent; petals white to pale lavender, 4–5 × 1.5–2 mm, glabrous; pollen ellipsoid. |
divaricate-ascending at anthesis; sepals glabrous or sparsely pubescent, trichomes spreading, 2-rayed; petals white to lavender, 4–5 × 1.5–1.8 mm, glabrous; pollen spheroid. |
Fruiting pedicels | divaricate-ascending to horizontal, slightly to strongly recurved, 3–8 mm, glabrous or sparsely pubescent, trichomes (isolated), simple. |
horizontal to divaricate-descending, straight or slightly curved downward, 2–5 mm, glabrous. |
Fruits | pendent, not appressed to rachis, not or, rarely, weakly secund, straight, edges parallel, 1.5–3.5 cm × 1.2–2 mm; valves glabrous; ovules 28–44 per ovary; style 0.1–0.4 mm. |
horizontal or divaricate-descending, not appressed to rachis, secund, straight, edges parallel, 1.6–3.2 cm × 1.5–2 mm; valves glabrous; ovules 20–32 per ovary; style 0.1–0.4 mm. |
Seeds | uniseriate, 0.9–1.2 × 0.6–1 mm; wing often continuous, 0.07–0.1 mm wide. |
uniseriate, 1.2–1.5 × 0.8–0.9 mm; not winged or with distal wing 0.05–0.1 mm wide. |
Boechera oxylobula |
Boechera pusilla |
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Phenology | Flowering May–Jul. | Flowering May–Jun. |
Habitat | Cliffs, rocky slopes, gravelly soil in sagebrush and open conifer forests | Cracks and crevices of granitic rock outcrops |
Elevation | 2100-3600 m (6900-11800 ft) | 2400-2500 m (7900-8200 ft) |
Distribution |
CO |
WY |
Discussion | Most of the collections assigned here have been called Arabis (Boechera) demissa by other authors (e.g., R. C. Rollins 1993; N. H. Holmgren 2005b). Because the holotype of A. demissa is identical to B. oxylobula in nearly every way (see M. D. Windham and I. A. Al-Shehbaz 2006 for detailed comparison), we treat them as conspecific. Boechera oxylobula is restricted to Garfield, Gunnison, Hinsdale, Lake, Mineral, Park, and Saguache counties in central Colorado. The taxon traditionally treated as A. (Boechera) demissa var. languida is here recognized as an apomictic species of hybrid origin (see Windham and Al-Shehbaz 2007b for detailed comparison). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Of conservation concern. Morphological evidence suggests that Boechera pusilla is an apomictic species that arose through hybridization between B. lemmonii and B. pendulina; it is known only from the type locality in southwestern Wyoming. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 391. | FNA vol. 7, p. 400. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Arabis oxylobula, Arabis aprica, Arabis demissa, Arabis rugocarpa, B. demissa | Arabis pusilla |
Name authority | (Greene) W. A. Weber: Phytologia 51: 370. (1982) | (Rollins) Dorn: Vasc. Pl. Wyoming ed. 3, 376. (2001) |
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