Boechera arcuata |
Boechera pauciflora |
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arching rockcress, elegant rockcress |
Columbia rockcress, few-flower rock-cress, fuzzy suncress, hairy-stem rock-cress, small-flower 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 1 per caudex branch, arising from center of rosette near ground surface, (1.4–)3–11.2 dm, densely pubescent proximally, trichomes simple, 0.6–1.5 mm, mixed with stalked, 2- (or 3-)rayed ones, 0.2–0.4 mm, 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, 3–10 mm wide, margins usually dentate, rarely entire, sometimes ciliate, trichomes (simple or branched), to 1 mm, surfaces densely pubescent, trichomes stalked, 2–5-rayed, 0.3–0.6 mm. |
Cauline leaves | 10–30(–45), often concealing stem proximally; blade auricles 2–5(–6) mm, surfaces of distalmost leaves pubescent. |
(8–)14–60, often concealing stem proximally; blade auricles (1–)3–10 mm, surfaces of distalmost leaves glabrous or sparsely pubescent. |
Racemes | 12–50(–70)-flowered, usually unbranched. |
17–60-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 at anthesis; sepals pubescent; petals lavender to whitish, 5–8 × 1–2 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-descending, usually straight, rarely slightly recurved, 4–13 mm, pubescent, trichomes spreading, 2- or 3-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. |
horizontal, divaricate-descending or widely pendent, not appressed to rachis, not secund, curved, edges parallel, 5.5–10.5 cm × 1.5–2.2 mm; valves glabrous; ovules 80–162 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, 1.4–1.8 × 1–1.4 mm; wing continuous, 0.1–0.25 mm wide. |
2n | = 21. |
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Boechera arcuata |
Boechera pauciflora |
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Phenology | Flowering Mar–Jun. | Flowering May–Jun. |
Habitat | Rocky hillsides and cliffs in pine forests and chaparral | Rocky soil in sagebrush areas, mountain shrub communities, edges of conifer forests |
Elevation | 300-1800 m (1000-5900 ft) | 600-2500 m (2000-8200 ft) |
Distribution |
CA
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CA; ID; MT; NV; OR; UT; WA; WY; BC
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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 pauciflora is an apomictic species that arose through hybridization between B. retrofracta and B. sparsiflora. Specimens of B. pauciflora are commonly identified as Arabis holboellii var. pinetorum (= B. pinetorum), a superficially similar species restricted to the northern Sierra Nevada and southern Cascade Range (see M. D. Windham and I. A. 2007 for detailed comparison). Arabis elegans A. Nelson (1900), not Tineo & Lojacono (1886) is an illegitimate name, sometimes found in synonymy with Boechera pauciflora. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 365. | FNA vol. 7, p. 393. |
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 | Sisymbrium pauciflorum, Arabis arcuata var. subvillosa, Arabis columbiana, Arabis perelegans, Arabis sparsiflora var. columbiana, Arabis sparsiflora var. subvillosa, B. sparsiflora var. subvillosa |
Name authority | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 268. (2007) |
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