59. Boechera microphylla (Nuttall) Dorn, Vasc. Pl. Wyoming, ed. 3, 376. 2001; Arabis microphylla Nuttall in Torrey & A. Gray, Fl. N. Amer. 1: 82. 1838. TYPE: United States, “Rocky Mountains”, T. Nuttall s.n. (holotype, RM!; isotype, PH!).
Arabis tenuicula Greene, Leafl. Bot. Observ. Crit. 2: 82. 1910. TYPE: United States, Oregon, Union County, in clefts of rocks, 3000 ft, May 1883, W. C. Cusick 1124 (holotype, US!; isotypes, GH!, NY!, OSC!, US!).
Plants long-lived, cespitose perennials, with woody caudices, lacking crowded, persistent leaf bases; sexual (with ellipsoid pollen) or apomictic (with spheroid pollen). Stems 1 or several per caudex branch, arising near ground surface from center or margin of basal rosettes, 0.8–2.8(–3.5) dm, lower parts with few simple and subsessile, 2-rayed trichomes 0.3–0.6 mm, upper parts glabrous. Leaves at stem bases oblanceolate to linear-oblanceolate, 1–4(–6) mm wide, entire or subapically few toothed, ciliate proximally with simple trichomes to 0.6 mm, blade surfaces densely pubescent with short-stalked, 4–8-rayed trichomes 0.05–0.1 mm; cauline leaves 2–6, not concealing stem, the uppermost glabrous, with auricles 0.5–1.5 mm. Inflorescences mostly unbranched, 5–17-flowered; fruiting pedicels 4–14 mm, ascending to divaricate-ascending, straight, glabrous. Flowers ascending at anthesis; sepals glabrous or pubescent; petals lavender to purple, 3.5–5.5 ´ 1.0–1.8 mm, glabrous; ovules 52–72 per fruit. Fruits 3–7 cm ´ 1.0–1.5 mm, ascending to divaricate-ascending, not appressed to rachises, not secund, straight to slightly curved, with parallel edges, glabrous; style 0.05–0.3 mm. Seeds uniseriate, 1.0–1.5 ´ 0.7–1.0 mm; wing often distal, ca. 0.1 mm wide. 2n = 14.
Habitat: cliffs and rocky slopes in sagebrush, mountain shrub, and open conifer forest.
Elevation: 430–2400 m.
Distribution: Canada (British Columbia), United States (Idaho, Montana, Nevada, Oregon, Utah, Washington, Wyoming).
Reproductive mode: sexual diploid.