Boechera collinsii
Boechera gracilipes
collin's suncress, Collins' rockcress
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, rarely arising laterally proximal to sterile shoots, 2.5–8.5 dm, densely pubescent proximally, trichomes simple or spurred, 0.9–1.5 mm, glabrous distally.
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, 5–12 mm wide, margins shallowly dentate, sometimes ciliate near petiole base, surfaces sparsely to densely pubescent, trichomes short- to long-stalked, 2- or 3-rayed, usually 0.3–0.6 mm.
(8–)15–40, concealing stem proximally;
blade auricles 1–3 mm, surfaces of distalmost leaves usually sparsely pubescent.
30–65, often concealing stem proximally;
blade auricles 0.8–3 mm, surfaces of distalmost leaves usually glabrous.
(15–)30–90-flowered, usually unbranched.
(12–)15–50-flowered, usually unbranched.
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 white to pale lavender, 6–9 × 0.6–1 mm;
valves glabrous;
pollen ellipsoid.
reflexed, abruptly recurved at base, otherwise straight, 4–13 mm, glabrous or sparsely pubescent, trichomes usually simple.
divaricate-ascending or horizontal, recurved, (15–)20–47 mm, glabrous.
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.
widely pendent, not appressed to rachis, not secund, curved, edges parallel, (2.5–)3–7.5 cm × 1.5–2.8 mm, glabrous;
ovules 130–210 per ovary;
style 0.2–0.5 mm.
uniseriate, 1–1.4 × 0.8–1 mm;
wing continuous (rarely absent), to 0.1 mm wide.
biseriate, 1.2–1.4 × 0.7–0.9 mm;
wing continuous or distal, to 0.2 mm wide.
= 14.
Boechera collinsii
Boechera gracilipes
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.)
Fruiting pedicel length, considered diagnostic by R. C. Rollins (1993) and N. H. Holmgren (2005b), occasionally fails to separate Boechera gracilipes from the closely-related B. fendleri. The two are consistently distinguished by trichome characters. In B. gracilipes, basal leaves usually lack prominent cilia and surfaces are persistently pubescent with at least some 3-rayed trichomes. Also, stems are rather densely pilose proximally, with the largest trichomes more than 0.9 mm. By contrast, basal leaves of B. fendleri always have prominent cilia, surfaces are often glabrescent, and 3-rayed trichomes usually are rare or absent. Stems of the latter are proximally hirsute to hispid, with the largest trichomes less than 0.9 mm.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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