47. Boechera howellii (S. Watson) Windham & Al-Shehbaz, Harvard Pap. Bot. 11: 69. 2006; Arabis howellii S. Watson, Proc. Amer. Acad. Arts 25: 124. 1890; A. platysperma A. Gray var. howellii (S. Watson) Jepson, Man. Fl. Pl. Calif. 432. 1925. TYPE: United States, Oregon, Jackson County, Siskiyou Mountains, Ashland Butte, 19 Jul 1887, T. Howell 664 (lectotype, designated by Jepson (Fl. Calif. 2: 72. 1936), GH!; isolectotypes, CAN!, MO!, NDG!, 5NY!, 2ORE!, 2PH!, US!).
Arabis conferta Greene, Repert. Sp. Nov. Regni Veg. 5: 243. 1908. TYPE: United States, California, Tuolumne Co., mountain slopes N Little Kern River,10-11000 ft, Sep 1897, C. A. Purpus 5231 (holotype, US!; isotypes, E!, GH!, K!, MO!, UC!).
Arabis inamoena Greene var. acutatus Jepson, Fl. Calif. 2: 72. 1936. TYPE: United States, California, Tuolumne Co., Young’s Lake, 9900 ft, 31 Jul 1927, F. W. Peirson 7610 (holotype, JEPS!).
Arabis platyloba Greene, Pittonia 4: 198. 1900. TYPE: United States, California, Lassen Co., Lake Solfataro, Lassen’ Peak, Jul 1896, Mrs. R. M. Austin (holotype, NDG!; isotypes, MO!, JEPS!, US!).
Arabis platysperma var. imparata Jepson, Fl. Calif. 2: 72. 1936. TYPE: United States, California, Lassen Co., Lake Solfataro, Lassen’ Peak, Jul 1896, Mrs. R. M. Austin (holotype, JEPS!; isotypes, MO!, NDG!, US!).
Plants long-lived perennials, with mostly woody caudices, lacking crowded, persistent leaf bases; sexual, ellipsoid pollen. Stems usually 1 per caudex branch, arising near ground surface from center of basal rosettes, 0.6–2(–3) dm, glabrous throughout. Leaves at stem bases narrowly oblanceolate, 1–7 mm wide, entire, ciliate proximally with simple and a few short-stalked, 2-rayed trichomes 0.1–0.4 mm, blade surfaces glabrous; cauline leaves 2–4, not concealing stem, the uppermost glabrous or (rarely) ciliate proximally, with auricles 0.2–1 mm or rarely lacking. Inflorescences unbranched, 2–5-flowered; fruiting pedicels 4–10 mm, ascending, straight, glabrous. Flowers erect to ascending at anthesis; sepals glabrous; petals white to dark lavender, 4–8 ´ 1.0–2.5 mm, glabrous; ovules 10–20 per fruit. Fruits 2.5–6.5 cm ´ 3–7 mm, suberect to ascending, usually not appressed to rachises, not secund, straight to curved, often with somewhat undulate (non-parallel) edges, glabrous; style 0.05–0.30 mm. Seeds uniseriate, 3–6 ´ 2–4 mm; wing continuous, 1.3–2.5 mm wide.
Habitat: rock outcrops, talus slopes and gravelly soil in alpine and subalpine habitats.
Elevation: 1800–3800 m.
Distribution: United States (California, Nevada, Oregon).
Reproductive mode: apomictic triploid.