Boechera arcuata |
Boechera rubicundula |
|
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arching rockcress, elegant rockcress |
Mount Day rockcress |
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Habit | Perennials; usually long-lived; sexual; caudex often woody (well-developed). | Perennials; long-lived; apomictic; caudex woody. |
Stems | usually 1 per caudex branch, arising from center of rosette, elevated on woody base or from ground surface, (2–)3–8 dm, densely pubescent proximally, trichomes short-stalked, 2-rayed and simple, to 1 mm, pubescent distally. |
usually 1 per caudex branch, arising from center of rosette, often somewhat elevated above ground surface on woody base, 1–5 dm, densely pubescent proximally, trichomes simple, 0.5–1 mm, mixed with long-stalked, 2- or 3-rayed ones, 0.1–0.5 mm, moderately to sparsely pubescent distally. |
Basal leaves | blade linear to oblanceolate, 2–7(–12) mm wide, margins usually entire, rarely denticulate, ciliate along petiole, trichomes to 1.5 mm, surfaces densely pubescent, trichomes usually short-stalked, 2–5-rayed (rarely some simple), 0.4–0.8 mm. |
blade oblanceolate, 4–8 mm wide, margins denticulate, ciliate along petiole, trichomes to 1 mm, surfaces densely pubescent, trichomes long-stalked, 2–5-rayed, 0.1–0.5 mm. |
Cauline leaves | 10–30(–45), often concealing stem proximally; blade auricles 2–5(–6) mm, surfaces of distalmost leaves pubescent. |
8–25, often concealing stem proximally; blade auricles 1–3 mm, surfaces of distalmost leaves moderately pubescent. |
Racemes | 12–50(–70)-flowered, usually unbranched. |
12–34-flowered, usually unbranched. |
Flowers | ascending at anthesis; sepals pubescent; petals purple, 9–14 × 2–4 mm, glabrous or sparsely pubescent (trichomes abaxially); pollen ellipsoid. |
ascending at anthesis; sepals pubescent; petals purplish, 6–8 × 2–2.5 mm, glabrous; pollen spheroid. |
Fruiting pedicels | usually divaricate-ascending, rarely horizontal, gently recurved or straight, 8–22 mm, pubescent, trichomes subappressed, 2–4-rayed. |
divaricate-ascending to horizontal, straight, 5–10 mm, pubescent, trichomes spreading, simple and 2-rayed. |
Fruits | usually divaricate-ascending, rarely horizontal, not appressed to rachis, not secund, usually curved, edges parallel, (6–)8–13 cm × 1.5–2.2 mm; valves glabrous or trichomes relatively few, scattered; ovules 90–250 per ovary; style 0.01–0.5 mm. |
divaricate-ascending to horizontal, not appressed to rachis, not secund, straight or slightly curved, edges parallel, 4–8 cm × 1.7–2.2 mm; valves glabrous; ovules 70–102 per ovary; style 0.1–0.3 mm. |
Seeds | uniseriate or sub-biseriate, 1.5–1.7 × 1–1.2 mm; wing continuous, 0.1–0.2 mm wide. |
uniseriate, 1.4–1.8 × 1–1.3 mm; wing continuous, 0.1–0.2 mm wide. |
Boechera arcuata |
Boechera rubicundula |
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Phenology | Flowering Mar–Jun. | Flowering Apr–May. |
Habitat | Rocky hillsides and cliffs in pine forests and chaparral | Mountain slopes |
Elevation | 300-1800 m (1000-5900 ft) | ca. 1200 m (ca. 3900 ft) |
Distribution |
CA
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CA |
Discussion | Although usually treated as a variety of Arabis (Boechera) sparsiflora (e.g., R. C. Rollins 1993), B. arcuata is easily distinguished from that species by having rachises and fruiting pedicels pubescent with subappressed, 2–4-rayed trichomes and a geographic range limited to southern and western California. By contrast, B. sparsiflora has rachises and fruiting pedicels with spreading, usually simple trichomes (sometimes glabrescent) and an allopatric distribution north and east of the Sierra Nevada. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Morphological evidence suggests that Boechera rubicundula is an apomictic species that arose through hybridization between B. arcuata and B. breweri (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison). It is known only from the type locality on Mt. Day in west-central California. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 365. | FNA vol. 7, p. 404. |
Parent taxa | Brassicaceae > tribe Boechereae > Boechera | Brassicaceae > tribe Boechereae > Boechera |
Sibling taxa | ||
Synonyms | Streptanthus arcuatus, Arabis holboellii var. arcuata, Arabis maxima, Arabis sparsiflora var. arcuata | Arabis arcuata var. rubicundula |
Name authority | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) | (Jepson) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 273. (2007) |
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