Arabis gunnisoniana Rollins, Rhodora 43: 434, fig. 3. 1941

Perennials; usually long-lived; (cespitose); sexual; caudex often woody. Stems usually 2-6 per caudex branch, arising from margin of rosette near ground surface, 0.8-2(-2.5) dm, densely pubescent proximally, trichomes short-stalked, 2-4-rayed, 0.08-0.3 mm, mixed with fewer simple ones, usually sparsely pubescent distally, rarely glabrous. Basal leaves: blade linear-oblanceolate, 1-3 (-4) mm wide, margins entire, ciliate proximally, trichomes to 0.8 mm, surfaces densely pubescent, trichomes short-stalked, 3-6-rayed, 0.08-0.3 mm. Cauline leaves: 3-9, not concealing stem; blade auricles 0.2-1 mm, surfaces of distalmost leaves glabrous or sparsely pubescent. Racemes 7-15-flowered, usually unbranched. Fruiting pedicels divaricate, straight or slightly curved, 4-7 mm, glabrous or sparsely pubescent, trichomes appressed, branched. Flowers divaricate-ascending at anthesis; sepals pubescent; petals white or lavender, 4-6 × 1-2 mm, glabrous; pollen ellipsoid. Fruits horizontal to divaricate-descending, not appressed to rachis, not secund, straight to slightly curved, edges parallel, 2.5-4 cm × 1-1.5 mm; valves glabrous; ovules 36-54 per ovary; style 0.1-0.2 mm. Seeds uniseriate, 1-1.2 × 0.8-1 mm; wing continuous, 0.1-0.15 mm wide. 2n = 14.

Flowering May-Jun. Rocky slopes and knolls with sagebrush; 2100-2700 m; Colo.

Boechera gunnisoniana is most similar to B. glareosa; it is distinguished from that species by having trichomes smaller (0.08-0.3 versus 0.3-0.6 mm) and more highly divided (mostly 2-4-rayed versus simple and 2-rayed) proximally on stems, and fewer (36-54 versus 50-80) ovules per ovary. The two species are allopatric, with B. glareosa known only from eastern Utah and extreme northwestern Colorado and B. gunnisoniana apparently endemic to Gunnison County in west-central Colorado.