Boechera collinsii |
Boechera rubicundula |
|
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collin's suncress, Collins' rockcress |
Mount Day rockcress |
|
Habit | Perennials; usually short-lived; sexual; caudex not woody. | Perennials; long-lived; apomictic; caudex 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, often somewhat elevated above ground surface on woody base, 1–5 dm, densely pubescent proximally, trichomes simple, 0.5–1 mm, mixed with long-stalked, 2- or 3-rayed ones, 0.1–0.5 mm, moderately to 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, 4–8 mm wide, margins denticulate, ciliate along petiole, trichomes to 1 mm, surfaces densely pubescent, trichomes long-stalked, 2–5-rayed, 0.1–0.5 mm. |
Cauline leaves | (8–)15–40, concealing stem proximally; blade auricles 1–3 mm, surfaces of distalmost leaves usually sparsely pubescent. |
8–25, often concealing stem proximally; blade auricles 1–3 mm, surfaces of distalmost leaves moderately pubescent. |
Racemes | (15–)30–90-flowered, usually unbranched. |
12–34-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. |
ascending at anthesis; sepals pubescent; petals purplish, 6–8 × 2–2.5 mm, glabrous; pollen spheroid. |
Fruiting pedicels | reflexed, abruptly recurved at base, otherwise straight, 4–13 mm, glabrous or sparsely pubescent, trichomes usually simple. |
divaricate-ascending to horizontal, straight, 5–10 mm, pubescent, trichomes spreading, simple and 2-rayed. |
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. |
divaricate-ascending to horizontal, not appressed to rachis, not secund, straight or slightly curved, edges parallel, 4–8 cm × 1.7–2.2 mm; valves glabrous; ovules 70–102 per ovary; style 0.1–0.3 mm. |
Seeds | uniseriate, 1–1.4 × 0.8–1 mm; wing continuous (rarely absent), to 0.1 mm wide. |
uniseriate, 1.4–1.8 × 1–1.3 mm; wing continuous, 0.1–0.2 mm wide. |
2n | = 14. |
|
Boechera collinsii |
Boechera rubicundula |
|
Phenology | Flowering May–Jun. | Flowering Apr–May. |
Habitat | Rocky and gravelly hillsides, prairies, open woods, floodplains | Mountain slopes |
Elevation | 600-1400 m (2000-4600 ft) | ca. 1200 m (ca. 3900 ft) |
Distribution |
ID; MN; MT; ND; NE; SD; WY; AB; MB; QC; SK
|
CA |
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 rubicundula is an apomictic species that arose through hybridization between B. arcuata and B. breweri (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison). It is known only from the type locality on Mt. Day in west-central California. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 370. | FNA vol. 7, p. 404. |
Parent taxa | Brassicaceae > tribe Boechereae > Boechera | Brassicaceae > tribe Boechereae > Boechera |
Sibling taxa | ||
Synonyms | Arabis collinsii, Arabis holboellii var. collinsii, Arabis retrofracta var. collinsii | Arabis arcuata var. rubicundula |
Name authority | (Fernald) Á. Löve & D. Löve: Taxon 31: 125. (1982) | (Jepson) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 273. (2007) |
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