Boechera arcuata |
Boechera porphyrea |
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arching rockcress, elegant rockcress |
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Habit | Perennials; usually long-lived; sexual; caudex often woody (well-developed). | Perennials; usually long-lived; apomictic; caudex often 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. |
1 to several per caudex branch, arising from center of rosette or arising laterally proximal to sterile shoots, somewhat elevated on woody base or from ground surface, 2–5(–9) dm, usually glabrous proximally, rarely sparsely pubescent, trichomes simple and short-stalked, 2- or 3-rayed, 0.1–0.5 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 oblanceolate, (3–)5–15 mm wide, margins dentate, ciliate at least along petiole, trichomes to 1 mm, surfaces pubescent, trichomes short-stalked, 2–6-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. |
5–17(–21), sometimes concealing stem proximally; blade auricles 0.5–3.5(–5.5) mm, surfaces of distalmost leaves glabrous. |
Racemes | 12–50(–70)-flowered, usually unbranched. |
10–30(–70)-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 glabrous; petals lavender, 6.5–8.5 × 1–2.5 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, gently curved downward, 10–27 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. |
widely pendent, not appressed to rachis, not secund, usually curved, edges parallel, 3–7 cm × 1.8–2.5 mm; valves glabrous; ovules 100–160 per ovary; style 0.2–0.5 mm. |
Seeds | uniseriate or sub-biseriate, 1.5–1.7 × 1–1.2 mm; wing continuous, 0.1–0.2 mm wide. |
sub-biseriate, 1.1–1.6 × 0.9–1.1 mm; wing continuous, 0.1–0.2 mm wide. |
Boechera arcuata |
Boechera porphyrea |
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Phenology | Flowering Mar–Jun. | Flowering late Mar-early May. |
Habitat | Rocky hillsides and cliffs in pine forests and chaparral | Rocky slopes in evergreen woodlands or desert scrub |
Elevation | 300-1800 m (1000-5900 ft) | 1200-2100 m (3900-6900 ft) |
Distribution |
CA
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NM; TX |
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 porphyrea is an apomictic species that arose through hybridization between B. texana and B. perennans (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 365. | FNA vol. 7, p. 398. |
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 porphyrea |
Name authority | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) | (Wooton & Standley) Windham: Harvard Pap. Bot. 11: 272. (2007) |
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