Boechera arcuata |
Boechera rigidissima |
|
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arching rockcress, elegant rockcress |
Trinity Mountain rockcress |
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Habit | Perennials; usually long-lived; sexual; caudex often woody (well-developed). | Perennials; long-lived; apomictic; caudex 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, slightly elevated on woody base or from near ground surface, 2–6 dm, pubescent proximally, trichomes usually subsessile, 2- or 3-rayed, rarely simple, 0.25–0.4 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, 2–6 mm wide, margins entire, ciliate proximally, trichomes to 0.7 mm, surfaces sparsely pubescent, trichomes subsessile to short-stalked, 2–5-rayed, 0.1–0.4 mm. |
Cauline leaves | 10–30(–45), often concealing stem proximally; blade auricles 2–5(–6) mm, surfaces of distalmost leaves pubescent. |
5–10, rarely concealing stem proximally; blade auricles 0.5–2 mm, surfaces of distalmost leaves glabrous. |
Racemes | 12–50(–70)-flowered, usually unbranched. |
5–16-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 purple, 6–8 × 1.5–2 mm, glabrous; pollen spheroid. |
Fruiting pedicels | usually divaricate-ascending, rarely horizontal, gently recurved or straight, 8–22 mm, pubescent, trichomes subappressed, 2–4-rayed. |
divaricate-ascending, straight, 4–10 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. |
divaricate-ascending, not appressed to rachis, not secund, straight, edges somewhat undulate (not parallel), 4–6.5(–7.6) cm × 2.5–3.5 mm; valves glabrous; ovules 24–54 per ovary; style 0.2–0.8 mm. |
Seeds | uniseriate or sub-biseriate, 1.5–1.7 × 1–1.2 mm; wing continuous, 0.1–0.2 mm wide. |
uniseriate, 2.5–3.2 × 1.8–2.5 mm; wing distal, 0.3–1 mm wide. |
Boechera arcuata |
Boechera rigidissima |
|
Phenology | Flowering Mar–Jun. | Flowering Jul–Aug. |
Habitat | Rocky hillsides and cliffs in pine forests and chaparral | Rocky places in open conifer forests |
Elevation | 300-1800 m (1000-5900 ft) | 1800-2000 m (5900-6600 ft) |
Distribution |
CA
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CA; NV |
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. Plants assigned to Boechera rigidissima appear to represent a series of apomictic hybrids, possibly involving B. stricta and B. suffrutescens. The two varieties recognized by Rollins are well isolated geographically (in Trinity County, California, and Washoe County, Nevada, respectively) and show enough morphological divergence to suggest that they represent distinct origins, if not different combinations of parental genomes. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 365. | FNA vol. 7, p. 403. |
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 rigidissima, Arabis rigidissima var. demota |
Name authority | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) | (Rollins) Al-Shehbaz: Novon 13: 389. (2003) |
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