Boechera arcuata |
Boechera falcatoria |
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arching rockcress, elegant rockcress |
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Habit | Perennials; usually long-lived; sexual; caudex often woody (well-developed). | Perennials; short- to long-lived; apomictic; caudex sometimes 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 2–7 per caudex branch, arising from margin of rosette near ground surface, 0.5–2(–3) dm, densely pubescent proximally, trichomes simple and stalked, 2-rayed, 0.3–0.8 mm, glabrous 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 narrowly oblanceolate, 1–3 mm wide, margins entire, ciliate, trichomes to 1 mm, surfaces pubescent, trichomes stalked, 2–4-rayed, 0.3–0.8 mm. |
Cauline leaves | 10–30(–45), often concealing stem proximally; blade auricles 2–5(–6) mm, surfaces of distalmost leaves pubescent. |
3–7(–10), not concealing stem; blade auricles 0.2–1 mm, surfaces of distalmost leaves glabrous. |
Racemes | 12–50(–70)-flowered, usually unbranched. |
6–15-flowered, 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 white or lavender, 5–7 × 1.5–2.5 mm, glabrous; pollen spheroid. |
Fruiting pedicels | usually divaricate-ascending, rarely horizontal, gently recurved or straight, 8–22 mm, pubescent, trichomes subappressed, 2–4-rayed. |
horizontal to divaricate-ascending, straight, 3–9 mm, glabrous. |
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. |
horizontal to divaricate-ascending, not appressed to rachis, not secund, usually strongly curved, edges parallel, 3.5–6.5 cm × 1.7–2 mm; valves glabrous; ovules 50–84 per ovary; style 0.05–0.5 mm. |
Seeds | uniseriate or sub-biseriate, 1.5–1.7 × 1–1.2 mm; wing continuous, 0.1–0.2 mm wide. |
uniseriate, 1.5–2 × 1.1–1.5 mm; wing continuous, 0.1–0.2 mm wide. |
Boechera arcuata |
Boechera falcatoria |
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Phenology | Flowering Mar–Jun. | Flowering May–Jun. |
Habitat | Rocky hillsides and cliffs in pine forests and chaparral | Rock outcrops and gravelly soil in sagebrush and mountain shrub communities |
Elevation | 300-1800 m (1000-5900 ft) | 2000-2200 m (6600-7200 ft) |
Distribution |
CA
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UT |
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.) |
Of conservation concern. Although the exact parentage of Boechera falcatoria, an apomictic hybrid, remains in doubt, it is virtually certain that B. cusickii contributed at least one genome. Boechera falcatoria has been confused with both B. pendulina and B. perennans, but is amply distinct from both (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison). Despite the proximity of the type locality to both Idaho and Nevada, the species is known only from northwestern Box Elder County. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 365. | FNA vol. 7, p. 376. |
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 falcatoria |
Name authority | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) | (Rollins) Dorn: Brittonia 55: 3. (2003) |
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