Boechera collinsii |
Boechera cascadensis |
|
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collin's suncress, Collins' rockcress |
Cascade rock-cress, Cascade suncress, Cascades rockcress, littleleaf rockcress |
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Habit | Perennials; usually short-lived; sexual; caudex not woody. | Perennials; long-lived; (cespitose); apomictic; caudex somewhat woody. |
Stems | usually 1 per caudex branch, arising from center of rosette near ground surface, (1.5–)2.5–8 dm, densely pubescent proximally, trichomes simple and short-stalked, 2-rayed, to 1 mm, sparsely pubescent or glabrous distally. |
usually 1 per caudex branch, arising from center of rosette near ground surface, 0.5–2.2 dm, sparsely pubescent proximally, trichomes simple and short-stalked, 2- or 3-rayed, 0.1–0.2 mm, glabrous distally. |
Basal leaves | blade oblanceolate, 1–7 mm wide, margins entire or dentate, ciliate along petiole, trichomes (simple), to 0.7 mm, surfaces moderately to densely pubescent, trichomes short-stalked, 5–8-rayed, 0.15–0.4 mm. |
blade linear-oblanceolate, 0.7–2 mm wide, margins entire, ciliate proximally, trichomes to 0.4 mm, surfaces densely pubescent, trichomes short-stalked, (2- or) 3–6-rayed, 0.05–0.2(–0.3) mm. |
Cauline leaves | (8–)15–40, concealing stem proximally; blade auricles 1–3 mm, surfaces of distalmost leaves usually sparsely pubescent. |
4–6, not concealing stem; blade auricles 0.5–1 mm, surfaces of distalmost leaves glabrous. |
Racemes | (15–)30–90-flowered, usually unbranched. |
3–11-flowered, unbranched. |
Flowers | descending to pendent at anthesis; sepals pubescent; petals usually white, rarely lavender, 4–6 × 0.8–1.5 mm, glabrous; pollen ellipsoid. |
ascending at anthesis; sepals glabrous or sparsely pubescent; petals lavender, 5–6 × 1–1.7 mm, glabrous; pollen spheroid. |
Fruiting pedicels | reflexed, abruptly recurved at base, otherwise straight, 4–13 mm, glabrous or sparsely pubescent, trichomes usually simple. |
ascending to divaricate-ascending, straight, 3–8 mm, glabrous. |
Fruits | strongly reflexed, usually appressed to rachis, rarely somewhat secund, straight, edges parallel, 3.5–6 cm × 0.9–1.5 mm; valves glabrous; ovules 70–126 per ovary; style 0.2–0.5 mm. |
ascending to divaricate-ascending, not appressed to rachis, not secund, straight, edges parallel, 3.5–6.2 cm × 1.2–1.5 mm; valves glabrous; ovules 58–80 per ovary; style 0.8–1.5 mm. |
Seeds | uniseriate, 1–1.4 × 0.8–1 mm; wing continuous (rarely absent), to 0.1 mm wide. |
uniseriate, 1.1–1.3 × 0.9–1 mm; wing continuous, 0.05–0.1 mm wide. |
2n | = 14. |
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Boechera collinsii |
Boechera cascadensis |
|
Phenology | Flowering May–Jun. | Flowering Jun. |
Habitat | Rocky and gravelly hillsides, prairies, open woods, floodplains | Basaltic cliffs and rocky slopes in subalpine areas |
Elevation | 600-1400 m (2000-4600 ft) | ca. 1900 m (ca. 6200 ft) |
Distribution |
ID; MN; MT; ND; NE; SD; WY; AB; MB; QC; SK
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OR; WA |
Discussion | Though often treated as a variety of Arabis (Boechera) holboellii (e.g., R. C. Rollins 1993; G. A. Mulligan 1996), B. collinsii is easily distinguished from that species by having simple and 2-rayed (versus 4–8-rayed) trichomes proximally on stems, and narrower (0.9–1.5 versus 2–2.5 mm) usually non-secund fruits. The two taxa also show allopatric distributions, with B. collinsii found on the North American continent (usually east of the Rocky Mountains) and B. holboellii apparently confined to Greenland. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Of conservation concern. Morphological evidence suggests that Boechera cascadensis is an apomictic species that arose through hybridization between B. microphylla and B. paupercula (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison). It is known from two collections: the type specimens from Kittitas County, Washington, and a more recent collection from Baker County, Oregon. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 370. | FNA vol. 7, p. 369. |
Parent taxa | Brassicaceae > tribe Boechereae > Boechera | Brassicaceae > tribe Boechereae > Boechera |
Sibling taxa | ||
Synonyms | Arabis collinsii, Arabis holboellii var. collinsii, Arabis retrofracta var. collinsii | Arabis microphylla var. thompsonii |
Name authority | (Fernald) Á. Löve & D. Löve: Taxon 31: 125. (1982) | Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 260. (2007) |
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