Boechera arcuata |
Boechera fernaldiana |
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arching rockcress, elegant rockcress |
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Habit | Perennials; usually long-lived; sexual; caudex often woody (well-developed). | Perennials; long-lived; (cespitose); sexual; caudex somewhat woody (sometimes with persistent, crowded leaf bases). | ||||
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 or slightly elevated on woody base, 1–3.8 dm, densely pubescent proximally, trichomes short-stalked, 4–8-rayed, 0.04–0.1 mm, sometimes mixed with stalked, 2-rayed ones, to 0.5 mm, usually sparsely pubescent distally. |
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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, 1–4 mm wide, margins entire, ciliate along petiole, trichomes (simple), to 1 mm, surfaces densely pubescent, trichomes short-stalked, 4–8-rayed, 0.04–0.1 mm. |
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Cauline leaves | 10–30(–45), often concealing stem proximally; blade auricles 2–5(–6) mm, surfaces of distalmost leaves pubescent. |
5–10, not concealing stem; blade auricles 0.3–2 mm, surfaces of distalmost leaves usually sparsely pubescent. |
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Racemes | 12–50(–70)-flowered, usually unbranched. |
10–20-flowered, usually unbranched. |
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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 (purplish or greenish) glabrous or sparsely or moderately pubescent; petals white or purple to lavender, 7–12 × 1.5–4 mm, glabrous; pollen ellipsoid. |
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Fruiting pedicels | usually divaricate-ascending, rarely horizontal, gently recurved or straight, 8–22 mm, pubescent, trichomes subappressed, 2–4-rayed. |
divaricate-ascending, straight, 5–20 mm, sparsely pubescent, trichomes appressed, branched. |
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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 or curved, edges parallel, 3.5–6.5(–7.5) cm × 1–1.6 mm; valves glabrous; ovules 30–72 per ovary; style 0.1–1 mm. |
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Seeds | uniseriate or sub-biseriate, 1.5–1.7 × 1–1.2 mm; wing continuous, 0.1–0.2 mm wide. |
uniseriate, 1–1.2 × 0.8–1 mm; wing continuous, ca. 0.1 mm wide. |
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Boechera arcuata |
Boechera fernaldiana |
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Phenology | Flowering Mar–Jun. | |||||
Habitat | Rocky hillsides and cliffs in pine forests and chaparral | |||||
Elevation | 300-1800 m (1000-5900 ft) | |||||
Distribution |
CA
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CO; NV; UT |
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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.) |
Subspecies 2 (2 in the flora). Taxa treated here as subspecies of Boechera fernaldiana share many morphological traits, and most recent authors (R. C. Rollins 1993; N. H. Holmgren 2005b) did not recognize them as distinct. They are consistently separated by the characters listed below, show some degree of molecular divergence (C. D. Bailey et al., unpubl.), and their ranges are separated by ca. 500 km. They clearly represent genetically isolated population systems that warrant taxonomic recognition. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 7, p. 365. | FNA vol. 7, p. 378. | ||||
Parent taxa | Brassicaceae > tribe Boechereae > Boechera | Brassicaceae > tribe Boechereae > Boechera | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Synonyms | Streptanthus arcuatus, Arabis holboellii var. arcuata, Arabis maxima, Arabis sparsiflora var. arcuata | Arabis fernaldiana, Arabis canescens var. stylosa, Arabis fernaldiana var. stylosa | ||||
Name authority | (Nuttall) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 64. (2006) | (Rollins) W. A. Weber: Phytologia 51: 370. (1982) | ||||
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