Boechera paupercula

Perennials; long-lived; (cespi-tose); sexual; caudex often woody. Stems usually 1 per caudex branch, arising from center of rosette near ground surface, 0.3-1.5 dm, densely pubescent proximally, trichomes simple and short-stalked, 2-4-rayed, (0.07-) 0.1-0.2 mm, glabrous or sparsely pubescent distally. Basal leaves: blade linear-oblanceolate, 1-3(-5) mm wide, margins entire, ciliate proximally, trichomes to 0.4 mm, surfaces densely pubescent, trichomes short-stalked, 2-6-rayed, (0.07-)0.1-0.2 mm. Cauline leaves: 2-6, rarely concealing stem; blade auricles 0 (or 0.2-1.5) mm, surfaces of distalmost leaves glabrous. Racemes 3-8 -flowered, unbranched. Fruiting pedicels erect, straight, 3-9 mm, glabrous or sparsely pubescent. Flowers erect at anthesis; sepals glabrous or sparsely pubescent; petals lavender to purplish, 4-6(-7) × 1-2 mm, glabrous; pollen ellipsoid. Fruits erect, appressed to rachis, not secund, straight, edges parallel, 2.5-5.5 cm × 1.3-1.7(-2) mm; valves glabrous; ovules 24-40 per ovary; style 0.2-1 mm. Seeds usually uniseriate, rarely sub-biseriate, 1.5-2 (-2.5) × 1-1.4 mm; wing continuous, 0.3-1 mm wide.

Flowering Jun-Aug. Rock outcrops, talus slopes, gravelly soil in alpine and subalpine habitats; 2400-3400 m; Calif., Idaho, Oreg., Wash., Wyo.

Boechera paupercula is usually subsumed under Arabis (Boechera) lyallii but is amply distinct (see M. D. Windham and I. A. Al-Shehbaz 2006 for detailed comparison).