Boechera williamsii |
Boechera cobrensis |
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cobre rock-cress, Masonic rock-cress, sagebrush rockcress |
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Habit | Perennials; short-lived; sexual; caudex not woody. | Perennials; long-lived; (often cespitose); sexual; caudex somewhat woody (usually without persistent leaf bases). |
Stems | usually 1 per caudex branch, arising from center of rosette near ground surface, 0.7–2.2 dm, glabrous throughout. |
usually 1 per caudex branch, arising from center of rosette near ground surface, (1.2–)2.5–6 dm, densely pubescent proximally, trichomes short-stalked, 4–10-rayed, 0.1–0.2 mm, sparsely pubescent or glabrous distally. |
Basal leaves | blade oblanceolate, 1–2 mm wide, margins entire, ciliate near petiole base, trichomes (simple), to 0.4 mm, surfaces sparsely to densely pubescent, trichomes short-stalked, 4–8-rayed, 0.03–0.1 mm. |
blade linear to narrowly oblanceolate, 1–4 mm wide, margins entire, ciliate near petiole base, trichomes (simple), to 0.6 mm, surfaces densely pubescent, trichomes short-stalked, 4–10-rayed, 0.1–0.2 mm. |
Cauline leaves | 6–11, sometimes concealing stem proximally; blade auricles to 0.5 mm, surfaces of distalmost leaves glabrous. |
5–10, not concealing stem; blade auricles 1–1.5 mm, surfaces of distalmost leaves usually sparsely pubescent. |
Racemes | 5–17-flowered, unbranched. |
10–25-flowered, often sparingly branched. |
Flowers | erect at anthesis; sepals glabrous; petals white, 3–4 × 0.5–0.8 mm, glabrous; pollen ellipsoid. |
divaricate-ascending at anthesis; sepals pubescent; petals white to lavender, 3.5–6 × 0.7–1 mm, glabrous; pollen ellipsoid. |
Fruiting pedicels | erect, straight, 2–4(–7) mm, glabrous. |
divaricate-ascending to horizontal, often straight proximally, usually strongly recurved or reflexed distally, 4–17 mm, usually pubescent, rarely glabrous, trichomes appressed, branched. |
Fruits | erect, usually appressed to rachis, not secund, straight, edges parallel, 2–3.5 cm × 2.2–2.5 mm; valves glabrous; ovules 60–96 per ovary; style 0.05–0.2 mm. |
pendent, not appressed to rachis, not secund, straight or slightly curved, edges parallel, 2.5–5.5 cm × 1.7–2.5 mm; valves glabrous; ovules 34–64 per ovary; style 0.05–0.2 mm. |
Seeds | sub-biseriate, 0.7–0.9 × 0.5–0.6 mm, not winged or minutely winged distally. |
uniseriate, 1.4–1.8 × 1–1.2 mm; wing continuous, 0.25–0.5 mm wide. |
2n | = 14. |
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Boechera williamsii |
Boechera cobrensis |
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Phenology | Flowering May–Jun. | Flowering May–Jun. |
Habitat | Gravelly soil in sagebrush-grassland communities | Sandy soil, usually under shelter of shrubs in semi-desert communities |
Elevation | 2300-2800 m (7500-9200 ft) | 1200-2800 m (3900-9200 ft) |
Distribution |
WY |
CA; ID; NV; OR; WY
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Discussion | Boechera williamsii is distinguished from all other sexual species of the genus by its combination of relatively short (3–4 mm), white petals, minute, 4–8-rayed trichomes on basal leaves, erect, appressed fruits, and relatively small, wingless seeds. It is known only from Fremont and Sublette counties in west-central Wyoming. The taxon traditionally treated as Arabis (Boechera) williamsii var. saximontana is here recognized as an apomictic species of hybrid origin (see M. D. Windham and I. A. Al-Shehbaz 2007b for detailed comparison). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Boechera cobrensis is a sexual diploid commonly found on stabilized sand dunes. The related B. lignifera often is found in similar habitats, and the two species can be difficult to distinguish where their ranges overlap in Idaho and Wyoming. It is possible that B. cobrensis was involved in the origin of some apomictic populations currently assigned to B. lignifera. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 411. | FNA vol. 7, p. 370. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Arabis williamsii | Arabis cobrensis |
Name authority | (Rollins) Dorn: Vasc. Pl. Wyoming ed. 3, 376. (2001) | (M. E. Jones) Dorn: Vasc. Pl. Wyoming ed. 3, 375. (2001) |
Web links |