Arabis pusilla Rollins, Contr. Gray Herb. 212: 107. 1982

Perennials; long-lived; (cespi-tose); apomictic; caudex often woody. Stems usually 2-6 per caudex branch, arising from margin of rosette near ground surface, 0.5-2 dm, glabrous or sparsely pubescent proximally, trichomes simple and short-stalked, 2-rayed, to 0.2 mm, glabrous distally. Basal leaves: blade linear-oblanceolate, 1-2.5 mm wide, margins entire, ciliate along petiole, trichomes (simple), 0.4-0.7 mm, surfaces usually sparsely pubescent, rarely glabrous, trichomes short-stalked, 2- or 3-rayed, 0.1-0.4 mm. Cauline leaves: 3-5, not concealing stem; blade auricles 0-0.2 mm, surfaces of distalmost leaves usually glabrous or, rarely, margins sparsely ciliate. Racemes 6-13-flowered, unbranched. Fruiting pedicels horizontal to divaricate-descending, straight or slightly curved downward, 2-5 mm, glabrous. Flowers divaricate-ascending at anthesis; sepals glabrous or sparsely pubescent, trichomes spreading, 2-rayed; petals white to lavender, 4-5 × 1.5-1.8 mm, glabrous; pollen spheroid. Fruits horizontal or divaricate-descending, not appressed to rachis, secund, straight, edges parallel, 1.6-3.2 cm × 1.5-2 mm; valves glabrous; ovules 20-32 per ovary; style 0.1-0.4 mm. Seeds uniseriate, 1.2-1.5 × 0.8-0.9 mm; not winged or with distal wing 0.05-0.1 mm wide.

Flowering May-Jun. Cracks and crevices of granitic rock outcrops; of conservation concern; 2400-2500 m; Wyo.

Morphological evidence suggests that Boechera pusilla is an apomictic species that arose through hybridization between B. lemmonii and B. pendulina; it is known only from the type locality in southwestern Wyoming.