Boechera falcatoria |
Boechera arcuata |
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arching rockcress, elegant rockcress |
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Habit | Perennials; short- to long-lived; apomictic; caudex sometimes woody. | Perennials; usually long-lived; sexual; caudex often woody (well-developed). |
Stems | 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. |
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. |
Basal leaves | 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. |
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. |
Cauline leaves | 3–7(–10), not concealing stem; blade auricles 0.2–1 mm, surfaces of distalmost leaves glabrous. |
10–30(–45), often concealing stem proximally; blade auricles 2–5(–6) mm, surfaces of distalmost leaves pubescent. |
Racemes | 6–15-flowered, unbranched. |
12–50(–70)-flowered, usually unbranched. |
Flowers | ascending at anthesis; sepals pubescent; petals white or lavender, 5–7 × 1.5–2.5 mm, glabrous; pollen spheroid. |
ascending at anthesis; sepals pubescent; petals purple, 9–14 × 2–4 mm, glabrous or sparsely pubescent (trichomes abaxially); pollen ellipsoid. |
Fruiting pedicels | horizontal to divaricate-ascending, straight, 3–9 mm, glabrous. |
usually divaricate-ascending, rarely horizontal, gently recurved or straight, 8–22 mm, pubescent, trichomes subappressed, 2–4-rayed. |
Fruits | 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. |
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. |
Seeds | uniseriate, 1.5–2 × 1.1–1.5 mm; wing continuous, 0.1–0.2 mm wide. |
uniseriate or sub-biseriate, 1.5–1.7 × 1–1.2 mm; wing continuous, 0.1–0.2 mm wide. |
Boechera falcatoria |
Boechera arcuata |
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Phenology | Flowering May–Jun. | Flowering Mar–Jun. |
Habitat | Rock outcrops and gravelly soil in sagebrush and mountain shrub communities | Rocky hillsides and cliffs in pine forests and chaparral |
Elevation | 2000-2200 m (6600-7200 ft) | 300-1800 m (1000-5900 ft) |
Distribution |
UT |
CA
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Discussion | 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.) |
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.) |
Source | FNA vol. 7, p. 376. | FNA vol. 7, p. 365. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Arabis falcatoria | Streptanthus arcuatus, Arabis holboellii var. arcuata, Arabis maxima, Arabis sparsiflora var. arcuata |
Name authority | (Rollins) Dorn: Brittonia 55: 3. (2003) | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) |
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