Boechera falcatoria
Boechera retrofracta
dangling suncress, reflexed rock-cress, secund rock-cress
usually 2–7 per caudex branch, arising from margin of rosette near ground surface, 0.5–2(–3) dm, densely pubescent proximally, trichomes simple and stalked, 2-rayed, 0.3–0.8 mm, glabrous distally.
usually 1 per caudex branch, arising from center of rosette near ground surface, 1.5–7(–10.5) dm, densely pubescent proximally, trichomes short-stalked, 2–8-rayed, 0.1–0.2 mm, sparsely pubescent distally.
blade narrowly oblanceolate, 1–3 mm wide, margins entire, ciliate, trichomes to 1 mm, surfaces pubescent, trichomes stalked, 2–4-rayed, 0.3–0.8 mm.
blade oblanceolate, 2–7 mm wide, margins entire or shallowly dentate, sometimes ciliate at petiole base, surfaces densely pubescent, trichomes short-stalked, 5–10-rayed, 0.05–0.2 mm.
3–7(–10), not concealing stem;
blade auricles 0.2–1 mm, surfaces of distalmost leaves glabrous.
15–40, concealing stem proximally;
blade auricles 0.5–2.5 mm or, rarely, absent, surfaces of distalmost leaves pubescent.
6–15-flowered, unbranched.
15–80(–140)-flowered, usually unbranched.
ascending at anthesis;
sepals pubescent;
petals white or lavender, 5–7 × 1.5–2.5 mm, glabrous;
pollen spheroid.
pendent at anthesis;
sepals pubescent;
petals white to lavender, 4–8 × 0.8–2.2 mm, glabrous;
pollen ellipsoid.
horizontal to divaricate-ascending, straight, 3–9 mm, glabrous.
reflexed, abruptly recurved at base, otherwise usually straight, 7–12(–18) mm, pubescent, trichomes appressed, branched.
horizontal to divaricate-ascending, not appressed to rachis, not secund, usually strongly curved, edges parallel, 3.5–6.5 cm × 1.7–2 mm;
valves glabrous;
ovules 50–84 per ovary;
style 0.05–0.5 mm.
strongly reflexed, usually appressed to rachis, sometimes somewhat secund, straight, edges parallel, 3.5–9 cm × 0.9–1.8 mm;
valves glabrous or sparsely pubescent throughout;
ovules 60–116 per ovary;
style 0.5–2 mm.
uniseriate, 1.5–2 × 1.1–1.5 mm;
wing continuous, 0.1–0.2 mm wide.
uniseriate, 1–1.4 × 0.9–1.2 mm;
wing continuous, to 0.1 mm wide.
= 14.
Boechera falcatoria
Boechera retrofracta
Of conservation concern.
Although the exact parentage of Boechera falcatoria, an apomictic hybrid, remains in doubt, it is virtually certain that B. cusickii contributed at least one genome. Boechera falcatoria has been confused with both B. pendulina and B. perennans, but is amply distinct from both (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison). Despite the proximity of the type locality to both Idaho and Nevada, the species is known only from northwestern Box Elder County.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Though often treated as a variety of Arabis (Boechera) holboellii (e.g., R. C. Rollins 1993; G. A. Mulligan 1996; N. H. Holmgren 2005b), B. retrofracta is easily distinguished from that species by having narrower (0.9–1.8 versus 2–2.5 mm), mostly non-secund fruits that are almost always appressed to rachises. The two taxa have allopatric distributions, with B. retrofracta found on the North American continent (mostly west of the Great Plains) and B. holboellii apparently confined to Greenland. Boechera retrofracta has formed hybrids with at least 12 other species. Besides differing in macromorphological characters, all those hybrids are distinct from B. retrofracta in the strict sense in having wider (20–30 versus 13–16 µm), spheroid pollen grains with asymmetric colpi.
Arabis kochii Blankinship is an illegitimate name, sometimes found in synonymy with Boechera retrofracta.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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