Boechera collinsii |
Boechera consanguinea |
|
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collin's suncress, Collins' rockcress |
Four Corners rockcress |
|
Habit | Perennials; usually short-lived; sexual; caudex not woody. | Biennials or perennials; short-lived; apomictic; caudex present or absent. |
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, 1.5–5 dm, densely pubescent proximally, trichomes short-stalked, 2–6-rayed, 0.2–0.5 mm, glabrous or sparsely pubescent 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 oblanceolate, 2–10 mm wide, margins usually dentate, sometimes ciliate near petiole base, trichomes (usually spurred), to 0.7 mm, surfaces moderately to densely pubescent, trichomes short-stalked, 4–8-rayed, 0.1–0.4 mm. |
Cauline leaves | (8–)15–40, concealing stem proximally; blade auricles 1–3 mm, surfaces of distalmost leaves usually sparsely pubescent. |
15–36, sometimes concealing stem proximally; blade auricles 1–3 mm, surfaces of distalmost leaves sparsely pubescent. |
Racemes | (15–)30–90-flowered, usually unbranched. |
20–55-flowered, usually unbranched. |
Flowers | descending to pendent at anthesis; sepals pubescent; petals usually white, rarely lavender, 4–6 × 0.8–1.5 mm, glabrous; pollen ellipsoid. |
divaricate-descending at anthesis; sepals pubescent; petals pale lavender, 5–8.5 × 1–2 mm, glabrous; pollen spheroid. |
Fruiting pedicels | reflexed, abruptly recurved at base, otherwise straight, 4–13 mm, glabrous or sparsely pubescent, trichomes usually simple. |
reflexed to divaricate-descending, usually curved downward, 8–14 mm, usually pubescent, rarely glabrous, trichomes subappressed, branched. |
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. |
reflexed to pendent, rarely appressed to rachis, not secund, straight or slightly curved, edges parallel, 4–6 cm × 1–2 mm; valves glabrous; ovules 100–128 per ovary; style 0.05–0.5 mm. |
Seeds | uniseriate, 1–1.4 × 0.8–1 mm; wing continuous (rarely absent), to 0.1 mm wide. |
biseriate to sub-biseriate, mature seeds not seen. |
2n | = 14. |
|
Boechera collinsii |
Boechera consanguinea |
|
Phenology | Flowering May–Jun. | Flowering May. |
Habitat | Rocky and gravelly hillsides, prairies, open woods, floodplains | Rocky slopes and sandy soil in ponderosa pine, pinyon-juniper, and sagebrush communities |
Elevation | 600-1400 m (2000-4600 ft) | 1900-2500 m (6200-8200 ft) |
Distribution |
ID; MN; MT; ND; NE; SD; WY; AB; MB; QC; SK
|
CO; NM; UT
|
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.) |
Morphological evidence suggests that Boechera consanguinea is an apomictic species that arose through hybridization between B. fendleri and B. retrofracta. It is most similar to B. goodrichii, another apomictic hybrid involving B. retrofracta (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. 370. | FNA vol. 7, p. 371. |
Parent taxa | Brassicaceae > tribe Boechereae > Boechera | Brassicaceae > tribe Boechereae > Boechera |
Sibling taxa | ||
Synonyms | Arabis collinsii, Arabis holboellii var. collinsii, Arabis retrofracta var. collinsii | Arabis consanguinea, Arabis holboellii var. consanguinea |
Name authority | (Fernald) Á. Löve & D. Löve: Taxon 31: 125. (1982) | (Greene) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 261. (2007) |
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