Arabis spatifolia Rydberg, Fl. Rocky Mts., 361, 1062. 1917; A. fendleri (S. Watson) Greene var. spatifolia (Rydberg) Rollins; Boechera fendleri (S. Watson) W. A. Weber subsp. spatifolia (Rydberg) W. A. Weber; B. fendleri var. spatifolia (Rydberg) Dorn

Perennials; short- to long-lived; sexual; caudex usually not woody (rarely with persistent, crowded leaf bases). Stems simple or few to several per caudex branch, arising from center of rosette near ground surface, 1.5-3.5(-5) dm, densely pubescent proximally, trichomes simple mixed with short-stalked ones, 2-rayed, 0.3-0.7 mm. Basal leaves: blade narrowly oblanceolate, 1.5-3(-4) mm wide, margins entire, strongly ciliate at least along petiole, trichomes (simple), to 1 mm, surfaces glabrous or sparsely pubescent, trichomes simple and short-stalked, 2-rayed, 0.3-0.7 mm. Cauline leaves: 5-15(-20), often concealing stem proximally; blade auricles 0.5-1.5 mm, surfaces of distalmost leaves usually glabrous. Racemes 10-30-flowered, usually unbranched. Fruiting pedicels horizontal or slightly descending, curved or angled downward, 6-10(-15) mm, usually glabrous, rarely sparsely pubescent, trichomes spreading, simple. Flowers divaricate-ascending at anthesis; sepals pubescent; petals usually white, rarely pale lavender, 3-3.7(-4) × 0.5-0.8 mm, glabrous; pollen ellipsoid. Fruits pendent, not appressed to rachis, rarely slightly secund, straight or gently curved, edges parallel, 3.3-5.7 cm × 1.2-1.8 mm; valves glabrous; ovules 90-126 per ovary; style 0.1-0.4 mm. Seeds biseriate, 0.7-0.9 × 0.5-0.6 mm; wing distal or, sometimes, absent, 0.05-0.1 mm wide. 2n = 14.

Flowering May-Aug. Rocky slopes and gravelly soil in sagebrush, pinyon-juniper woodlands, open conifer forests and subalpine meadows; 1800-2800 m; Colo., N.Mex.

Boechera spatifolia is a sexual diploid that usually has been treated as a variety of Arabis (Boechera) fendleri but appears to be sufficiently distinct to warrant recognition at species level (see M. D. Windham and I. A. Al-Shehbaz 2006 for detailed comparison). There is little geographic overlap between the two, with B. spatifolia confined to the mountains of central Colorado and north-central New Mexico and B. fendleri ranging from western New Mexico and the Four Corners region through northern Arizona to southern Nevada.