Boechera arcuata |
Boechera holboellii |
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arching rockcress, elegant rockcress |
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Habit | Perennials; usually long-lived; sexual; caudex often woody (well-developed). | Biennials or perennials; short-lived; apomictic or sexual; caudex present or absent. |
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 near ground surface, 2–6.7 dm, densely pubescent proximally, trichomes short-stalked, 4–8-rayed, 0.1–0.3 mm, glabrous or 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, 2–5 mm wide, margins entire, sometimes ciliate near petiole base, trichomes (usually simple), to 0.7 mm, surfaces sparsely to moderately pubescent, trichomes short-stalked, 4–8-rayed, 0.1–0.3 mm. |
Cauline leaves | 10–30(–45), often concealing stem proximally; blade auricles 2–5(–6) mm, surfaces of distalmost leaves pubescent. |
7–40, often concealing stem proximally; blade auricles 1–4 mm, surfaces of distalmost leaves glabrous or sparsely pubescent. |
Racemes | 12–50(–70)-flowered, usually unbranched. |
10–60-flowered, usually unbranched. |
Flowers | ascending at anthesis; sepals pubescent; petals purple, 9–14 × 2–4 mm, glabrous or sparsely pubescent (trichomes abaxially); pollen ellipsoid. |
divaricate to pendent at anthesis; sepals pubescent; petals white, 4–8 × 1–2 mm, glabrous; pollen ellipsoid or spheroid. |
Fruiting pedicels | usually divaricate-ascending, rarely horizontal, gently recurved or straight, 8–22 mm, pubescent, trichomes subappressed, 2–4-rayed. |
descending to reflexed, most abruptly recurved near base, 5–10 mm, glabrous or sparsely pubescent, trichomes appressed, branched. |
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. |
descending to reflexed, not appressed to rachis, strongly secund, often curved, edges parallel, 0.35–0.65 cm × (2–)2.2–2.5 mm; valves glabrous; ovules 80–102 per ovary. |
Seeds | uniseriate or sub-biseriate, 1.5–1.7 × 1–1.2 mm; wing continuous, 0.1–0.2 mm wide. |
uniseriate to sub-biseriate, 1.4–1.7 × 1–1.2 mm; wing continuous, to 0.2 mm wide. |
2n | = 14, 21. |
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Boechera arcuata |
Boechera holboellii |
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Phenology | Flowering Mar–Jun. | Flowering Jul–Aug. |
Habitat | Rocky hillsides and cliffs in pine forests and chaparral | Rocky slopes and gravelly soil near coast |
Elevation | 300-1800 m (1000-5900 ft) | 100-300 m (300-1000 ft) |
Distribution |
CA
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Greenland |
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.) |
Both sexual diploid and apomictic triploid collections of Boechera holboellii are known; available data suggest that the triploid is an autopolyploid derivative of the sexual diploid but further study is needed. In the narrow circumscription adopted here, it appears to be restricted to Greenland (see discussion of B. quebecensis in M. D. Windham and I. A. Al-Shehbaz 2007b). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 365. | FNA vol. 7, p. 384. |
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 holboellii, Arabis holboellii var. tenuis, B. tenuis |
Name authority | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) | (Hornemann) Á. Löve & D. Löve: Bot. Not. 128: 513. (1976) |
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