23. Boechera drepanoloba (Greene) Windham & Al-Shehbaz, Harvard Pap. Bot. 11: 263. 2007.
Arabis drepanoloba Greene, Pittonia 3: 306. 1898; A. drummondii A. Gray var. oreophila (Rydberg) M. Hopkins; A. lemmonii S. Watson var. drepanoloba (Greene) Rollins; A. oreophila Rydberg
Perennials; short- to long-lived; apomictic; caudex usually not woody. Stems usually 1 per caudex branch, arising from center of rosette near ground surface, 1-4 dm, glabrous or sparsely pubescent proximally, trichomes sessile or subsessile, 2- or 3-rayed, 0.1-0.3 mm, glabrous distally. Basal leaves: blade oblanceolate, 2-6 mm wide, margins entire, ciliate along petiole, trichomes (submalpighiaceous or simple), to 0.6 mm, surfaces sparsely to densely pubescent, trichomes subsessile, 2-6-rayed, 0.1-0.3 mm. Cauline leaves: 3-15, often concealing stem proximally; blade auricles 0.7-2.5 mm, surfaces of distalmost leaves usually glabrous. Racemes 5-25-flowered, usually unbranched. Fruiting pedicels horizontal to ascending, straight or curved, 4-8 mm, glabrous. Flowers ascending at anthesis; sepals glabrous or pubescent with scattered trichomes; petals purple to lavender, 6-8 × 1.5-2.5 mm, glabrous; pollen spheroid. Fruits horizontal to ascending, secund, straight to slightly curved, edges parallel, 3-5.8 cm × 2-3.5 mm; valves glabrous; ovules 44-76(-104) per ovary; style 0.05-0.5 mm. Seeds uniseriate, 1.5-2.2 × 1.2-1.6 mm; wing continuous, 0.3-0.7 mm wide.
Flowering Jul-Aug. Rocky slopes and talus in alpine and subalpine habitats; 2000-3800 m; Alta.; Alaska, Colo., Idaho, Mont., Oreg., Utah, Wash., Wyo.
Morphological evidence suggests that Boechera drepanoloba is an apomictic species that arose through hybridization between B. lemmonii and B. stricta (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison).