17. Boechera cusickii (S. Watson) Al-Shehbaz, Novon. 13: 384. 2003.
Arabis cusickii S. Watson, Proc. Amer. Acad. Arts 17: 363. 1882
Perennials; long-lived; (often cespitose); sexual; caudex usually woody. Stems usually 1 per caudex branch, arising from center of rosette near ground surface, 1-2.5(-3.8) dm, densely pubescent proximally, trichomes simple, 0.5-1.5 mm, sparsely pubescent or glabrous distally. Basal leaves: blade linear to narrowly oblanceolate, 0.5-2 mm wide, margins entire, ciliate, trichomes (simple), 1-1.7 mm, surfaces moderately pubescent, trichomes simple and long-stalked, 2-rayed, 0.5-1.7 mm. Cauline leaves: 10-30, often concealing stem proximally; blade auricles 0-0.5 mm, surfaces of distalmost leaves sparsely pubescent. Racemes 5-14-flowered, usually unbranched. Fruiting pedicels ascending, straight, 4-15(-20) mm, glabrous or sparsely pubescent, trichomes simple. Flowers ascending at anthesis; sepals pubescent; petals white to lavender, 6-10 × 2-3 mm, glabrous; pollen ellipsoid. Fruits ascending to divaricate-ascending, not appressed to rachis, not secund, straight or curved, edges parallel, 4-8(-9.5) cm × 2.3-3 mm; valves glabrous; ovules 56-106 per ovary; style 0.1-0.5 mm. Seeds uniseriate, 1.5-2.5 × 1.5-2 mm; wing continuous, 0.1-0.2 mm wide distally.
Flowering Apr-mid May. Basaltic bluffs, rocky slopes, rock crevices, gravelly hillsides, sagebrush hills, outcrops of volcanic rock; 600-1800 m; Idaho, Nev., Oreg., Wash.
Peripheral populations of Boechera cusickii in south-central Idaho and northern Nevada have a higher proportion of branched hairs, possibly resulting from hybridization with B. sparsiflora.