1. Boechera acutina (Greene) Windham & Al-Shehbaz, Harvard Pap. Bot. 12: 236. 2007; Arabis acutina Greene, Leafl. Bot. Observ. Crit. 2: 82. 1910. TYPE: United States, Oregon, Mount Thielson, Cascade Mts., 6 August 1897, Frederick V. Coville & Elmer I. Applegate 434 (Lectototype: US; Isolectotypes: DS, RM, US, WILLU).
Arabis interposita Greene, Leafl. Bot. Observ. Crit. 2: 78. 1910; A. drummondii A. Gray var. interposita (Greene) Rollins, Res. Stud. State Coll. Wash. 4: 45. 1936; A. divaricarpa A. Nelson var. interposita (Greene) Rollins, Rhodora 43: 378. 1941. TYPE: United States, Oregon, Ashland Butte, Siskiyou Mts., and near Crater Lake, Cascade Mts., 14 July and 22 August 1902, W. C. Cusick 2970 (holotype: US!; isotypes: GH!, NY1, OSC1).
Plants short-lived perennials or biennials, with or without 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, 1.5–6.0 dm, lower parts with many, sessile, 2–4-rayed trichomes 0.15–0.40 mm, upper parts sparsely pubescent or rarely glabrous. Leaves at stem bases oblanceolate, 1.5–6.0 mm wide, entire or rarely denticulate, ciliate proximally with simple trichomes to 0.5 mm, blade surfaces sparsely to moderately pubescent with sessile, 3–5(–6)-rayed trichomes 0.15–0.35 mm; cauline leaves 2–20(–38), often concealing stem proximally, the uppermost sparsely pubescent or glabrous, with auricles 0.3–2.0 mm. Inflorescences mostly unbranched, 5–20(–36)-flowered; fruiting pedicels 3–10 mm, erect to ascending, mostly straight, with appressed, branched trichomes or glabrous. Flowers ascending at anthesis; sepals pubescent; petals white or lavender, 5–7 ´ 0.9–1.3 mm, glabrous; ovules 46–100 per fruit. Fruits 2.5–7.5 cm ´ 1.2–1.8 mm, ascending, not appressed to rachises, not secund, straight, with parallel edges, glabrous; style 0.3–1.0 mm. Seeds uniseriate, 1.8–2.2 ´ 1.0–1.4 mm; wing continuous, 0.1–0.4 mm wide.
Habitat: gravelly slopes in meadows and open forests.
Elevation: 1400–1850 m.
Distribution: United States (California, Idaho, Oregon).
Reproductive mode: triploid apomict.