57. Boechera lyallii (S. Watson) Dorn, Vasc. Pl. Wyoming, ed. 3. 376. 2001; Arabis lyallii S. Watson, Proc. Amer. Acad. Arts 11: 122. 1876; A. drummondii A. Gray var. alpina S. Wats., Botany [Fortieth Parallel] 18. 1871; A. drummondii var. lyallii (S. Wats.) Jepson, Man. Fl. Pl. Calif. 429. 1925. TYPE: United States, Nevada, Elko County, Clover Mts. [East Humboldt Range], 10,000 ft, Sep 1868, S. Watson 75 (lectotype designated by Hopkins (1937: 141), GH!).
Arabis armerifolia Greene, Leafl. Bot. Observ. Crit. 2: 75. 1910. TYPE: United States, Oregon, Klamath County, Crater Lake National Park, fine pumice slope, 14 Sep 1902, F. V. Coville 1504 (holotype, US!).
Arabis densa Greene, Leafl. Bot. Observ. Crit. 2: 76. 1910. TYPE: United States, Oregon, Union County, Eagle Cap, Imnaha National Forest, 9500 feet (as 9000 feet in protologue), 14 Sep 1907, A. W.Sampson & G. A. Pearson 206 (holotype, US!).
Arabis multiceps Greene, Leafl. Bot. Observ. Crit. 2: 76. 1910. TYPE: United States, Oregon, Douglas County, Mt. Thielson, Cascade Range, open rocky slopes, 6 Aug 1897, F. V. Coville & E. I. Applegate 435 (holotype, US!; isotypes, DS!, NY!, RM!).
Arabis murrayi G. A. Mulligan, Rhodora 97: 151. 1996. TYPE: Canada, Yukon, Kaskawulsh nunatak, jct. north and central arms Kaskaulsh Glacier, W of Kluane Lake, 1 Jul–1 Aug 1965, 6000 ft, D. F. & B. M. Murray 91b (holotype, DAO!; isotype, ALA!).
Plants long-lived, cespitose perennials, with woody caudices, lacking crowded, persistent leaf bases; sexual (with ellipsoid pollen) or apomictic (with spheroid pollen). Stems usually 1 per caudex branch, arising near ground surface from center of basal rosettes, 0.3–1.5(–2) dm, glabrous throughout. Leaves at stem bases linear-oblanceolate, 1–5(–8) mm wide, margin entire, usually ciliate at least proximally with simple and/or short-stalked, 2- or 3-rayed trichomes 0.1–0.3 mm, blade surfaces (occasionally the entire leaf) glabrous or rarely the youngest leaves of sterile shoots pubescent with 4–6-rayed trichomes 0.05–0.10 mm; cauline leaves 1–5, mostly not concealing stem, glabrous, with auricles 0.5–1.5 mm or rarely lacking. Inflorescences unbranched, 2–10(–15)-flowered; fruiting pedicels 3–8(–15) mm, erect, straight, glabrous. Flowers erect at anthesis; sepals glabrous; petals lavender to purplish, 6.0–8.5 ´ 1.5–3.0 mm, glabrous; ovules 34–64 per fruit. Fruits 3.0–5.6 cm ´ 1.5–2.5 mm, erect, appressed to rachises, not secund, straight, with parallel edges, glabrous; style 0.1–0.7 mm. Seeds biseriate or subbiseriate, 1.5–2.0 ´ 1.0–1.5 mm; wing continuous, 0.3–0.5 mm wide.
Habitat: cliffs, talus slopes, and gravelly soil in alpine and subalpine habitats.
Elevation: 1450–3700 m.
Distribution: Canada (British Columbia, Yukon), United States (California, Idaho, Montana, Nevada, Oregon, Utah, Washington).
Reproductive mode: sexual diploid.