Arabis macounii S. Watson, Proc. Amer. Acad. Arts 26: 124. 1891; A. densicaulis A. Nelson; A. microphylla Nuttall var. macounii (S. Watson) Rollins

Perennials; usually long-lived; apomictic; caudex often woody. Stems 1 or several per caudex branch, arising from center or margin of rosette near ground surface, 2-3.6 dm, densely pubescent proximally, trichomes simple and short-stalked, 2-rayed, 0.1-0.8 mm, glabrous distally. Basal leaves: blade oblanceolate to linear-oblanceolate, 1-3(-5) mm wide, margins entire or minutely toothed, ciliate proximally, trichomes (simple), to 0.7 mm, surfaces densely pubescent, trichomes short-stalked, 3-6-rayed, 0.07-0.3 mm. Cauline leaves: (5-)9-16, often concealing stem proximally; blade auricles 0.5-1.5 mm, surfaces of distalmost leaves glabrous. Racemes 10-33-flowered, usually unbranched. Fruiting pedicels divaricate-ascending to horizontal, straight, 5-13 (-17) mm, usually densely pubescent, rarely glabrous, trichomes appressed, 2- or 3-rayed. Flowers divaricate-ascending at anthesis; sepals pubescent; petals lavender to purple, 4-5 × 0.5-0.8 mm, glabrous; pollen spheroid. Fruits divaricate-ascending to descending, not appressed to rachis, not secund, usually curved, edges parallel, 3.5-6.5 cm × 0.8-1.2 mm; valves glabrous; ovules 56-78 per ovary; style 0.1-0.4 mm. Seeds uniseriate, 1-1.2 × 0.7-1 mm; wing often continuous, 0.05-0.15 mm wide.

Flowering May-Jul. Rocky hillsides in open pinewoods; 2200-2900 m; B.C.; Idaho, Mont., Wyo.

Morphological evidence suggests that Boechera macounii is an apomictic species that arose through hybridization between B. collinsii and B. microphylla (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison).