Boechera oxylobula |
Boechera johnstonii |
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Johnston's rockcress |
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Habit | Perennials; short- to long-lived; (cespitose); sexual; caudex usually not woody. | Perennials; long-lived; (cespitose); sexual; caudex 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 1 per caudex branch, arising from center of rosette near ground surface, 0.5–2 dm, densely pubescent proximally, trichomes short-stalked, 4–10-rayed, 0.07–0.15 mm, sparsely to densely pubescent 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 narrowly oblanceolate, 1.5–4 mm wide, margins entire, not ciliate, surfaces densely pubescent, trichomes short-stalked, 6–14-rayed, 0.07–0.15 mm. |
Cauline leaves | 3–12, not concealing stem; blade auricles absent, surfaces of distalmost leaves usually glabrous, rarely sparsely pubescent. |
4–10, often concealing stem proximally; blade auricles absent, surfaces of distalmost leaves densely pubescent. |
Racemes | 2–12-flowered, unbranched. |
10–18-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. |
ascending at anthesis; sepals pubescent; petals purple, 9–14 × 2–4 mm, glabrous; pollen ellipsoid. |
Fruiting pedicels | divaricate-ascending to horizontal, slightly to strongly recurved, 3–8 mm, glabrous or sparsely pubescent, trichomes (isolated), simple. |
divaricate-ascending, straight, 5–14 mm, pubescent, trichomes appressed, branched. |
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. |
divaricate-ascending, not appressed to rachis, not secund, straight, edges parallel, 4–6 cm × 2.5–4 mm; valves glabrous; ovules 26–34 per ovary; style (0.7–)1–2 mm. |
Seeds | uniseriate, 0.9–1.2 × 0.6–1 mm; wing often continuous, 0.07–0.1 mm wide. |
uniseriate, 1.9–2.7 × 1.5–2.2 mm; wing continuous, 0.3–0.7 mm wide. |
Boechera oxylobula |
Boechera johnstonii |
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Phenology | Flowering May–Jul. | Flowering Feb–Mar. |
Habitat | Cliffs, rocky slopes, gravelly soil in sagebrush and open conifer forests | Rocky areas and gravelly soil in chaparral and oak-pine savannas |
Elevation | 2100-3600 m (6900-11800 ft) | 1300-1700 m (4300-5600 ft) |
Distribution |
CO |
CA |
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. Boechera johnstonii and B. hirshbergiae are too similar to be considered distinct species. Even with the expanded circumscription, this distinctive sexual species is known only from the area of Cuyamaca Lake (San Diego County) and the San Jacinto Mountains (Riverside County). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 391. | FNA vol. 7, p. 386. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Arabis oxylobula, Arabis aprica, Arabis demissa, Arabis rugocarpa, B. demissa | Arabis johnstonii, Arabis hirshbergiae, B. hirshbergiae |
Name authority | (Greene) W. A. Weber: Phytologia 51: 370. (1982) | (Munz) Al-Shehbaz: Novon 13: 386. (2003) |
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