10. Boechera cascadensis Windham & Al-Shehbaz, Harvard Pap. Bot. 11: 260. 2007; Arabis microphylla Nuttall var. thompsonii Rollins, Rhodora 43: 429. 1941, not Boechera thompsonii (S. L. Welsh) N. H. Holmgren in N. H. Holmgren et al., Intermountain Fl. 2b: 374. 2005. TYPE: United States, Washington, Kittitas County, alpine meadows of Table Mt., 5000 ft [1515 m], 3 July 1933, J. W. Thompson 9266 (holotype, GH!; isotypes; MO!, NY!, US!).
Plants long-lived, cespitose perennials, with somewhat woody caudices; lacking crowded, persistent leaf bases; apomictic, with spheroid pollen. Stems usually 1 per caudex branch, arising near ground surface from center of basal rosettes, 0.5–2.2 dm, lower parts with few simple and short-stalked, 2–3-rayed trichomes 0.1–0.2 mm, upper parts glabrous. Leaves at stem bases linear-oblanceolate, 0.7–2.0 mm wide, entire, ciliate proximally with trichomes to 0.4 mm, blade surfaces densely pubescent with short-stalked, (2–)3–6-rayed trichomes 0.05–0.2(–0.3) mm; cauline leaves 4–6, not concealing stem, the uppermost glabrous, with auricles 0.5–1 mm. Inflorescences unbranched, 3–11-flowered; fruiting pedicels 3–8 mm, ascending to divaricate-ascending, straight, glabrous. Flowers ascending at anthesis; sepals glabrous or sparsely pubescent; petals lavender, 5–6 ´ 1.0–1.7 mm, glabrous; ovules 58–80 per fruit. Fruits 3.5–6.2 cm ´ 1.2–1.5 mm, ascending to divaricate-ascending, not appressed to rachises, not secund, straight, with parallel edges, glabrous; style 0.8–1.5 mm. Seeds uniseriate, 1.1–1.3 ´ 0.9–1.0 mm; wing continuous, 0.05–0.1 mm wide.
Habitat: basaltic cliffs and rocky slopes in subalpine areas.
Elevation: ca. 1900 m.
Distribution: United States (Oregon, Washington).
Reproductive mode: apomictic triploid.