Boechera atrorubens
black-flower rockcress, dark-red-flower rockcress, purple sickle-pod rock-cress, sicklepod rockcress
usually 1 per caudex branch, arising from center of rosette near ground surface, 0.8–6 dm, sparsely pubescent proximally, trichomes short-stalked and simple, (scattered), 2-rayed, 0.1–0.15 mm, glabrous distally.
blade oblanceolate, 4–10 mm wide, margins usually dentate, not ciliate, surfaces densely pubescent, trichomes short-stalked, 3- or 4-rayed, 0.1–0.2 mm.
7–25, concealing stem proximally;
blade auricles 1–4 mm, surfaces of distalmost leaves glabrous.
6–20-flowered, usually unbranched.
ascending at anthesis;
sepals pubescent;
petals dark reddish purple (drying indigo), 7–9 × 1.5–2 mm, glabrous;
pollen ellipsoid.
ascending, usually straight, 5–10 mm, glabrous or pubescent, trichomes spreading, simple.
ascending, not appressed to rachis, not secund, curved or straight, edges parallel, (4–)6–12 cm × 1.7–2.2 mm;
valves glabrous;
ovules 80–100 per ovary;
style 0.2–0.5 mm.
uniseriate, 1.2–1.7 × 0.9–1.2 mm;
wing lateral and distal, 0.1–0.2 mm wide.
Boechera atrorubens
Boechera atrorubens is often treated as a variety of B. sparsiflora (e.g., R. C. Rollins 1993), it is readily separated from that species by having proximal stems sparsely (versus densely) pubescent with much smaller (0.15 versus 1.5 mm) trichomes. The two taxa rarely grow in proximity and, in areas where they are sympatric, B. atrorubens is further distinguished by its narrower (1.5–2 versus 2–5 mm) petals that are dark reddish purple to indigo (versus lavender or white).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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