87. Boechera retrofracta (Graham) A. Löve & D. Löve, Taxon 31: 125. 1982; Arabis retrofracta Graham, Edinburgh New Philos. J. 1829: 344. 1829; Turritis retrofracta (Graham) W. J. Hooker, Fl. Bor. Amer. 1: 41. 1829; A. holboellii Hornem. var. retrofracta (Graham) Rydberg, Contr. U.S. Natl. Herb. 3: 484. 1896. TYPE: U.S.A. “Raised at the Botanic Garden from seeds collected [by J. Richardson] in Captain Franklin’s last [1819–1822] expedition from Hudson’s Bay to the Rocky Mountains and from Canada to Lat. 68° at Mackenzie’s River” (lectotype designated by Windham & Al-Shehbaz (2006: 79) as the second plant from the right of sheet, K!).
Arabis secunda Howell, Erythea 3: 33. 1895; A. arcuata (Nuttall) var. secunda (Howell) B. L. Robinson in A. Gray & S. Watson, Syn. Fl. N. Amer. 1(1): 164. 1895; A. holboellii var. secunda (Howell) Jepson, Man. Fl. Pl. Calif. 430. 1925; Boechera holboellii (Graham) Á. Löve & D. Löve var. secunda (Howell) Dorn, Vasc. Pl. Wyoming, ed. 3. 376. 2001. TYPE: United States, Washington, Yakima County, Mt. Adams, Aug 1882, T. Howell 1487 (holotype, ORE!; isotypes, JEPS!, MO!, NY!, PH!, UC!, US!, WS!).
Arabis exilis A. Nelson, Bull. Torrey Bot. Club 26: 123. 1899; Boechera exilis (A. Nelson) Dorn, Vasc. Pl. Wyoming, ed. 3. 375. 2001. TYPE: United States, Wyoming, Uinta County, Evanston, 4 Jun 1898, A. Nelson 4523 (holotype, RM!; isotypes, GH!, MO!, NY!; US!).
Arabis lignipes A. Nelson, Bot. Gaz. 30: 191. 1900. TYPE: United States, Wyoming, Yellowstone National Park, stony flats near Madison River, 23 Jun 1899, A. Nelson & E. Nelson 5505 (Lectotype, designated by Rollins (1941: 443), RM!; isolectotypes, DS!, E!, GH!, K!, MO!, NDG!, NMC!, NY!, POM!, 2RM!, US!).
Arabis tenuis Greene, Pittonia 4: 189. 1900. TYPE: United States, Washington, Klickitat County, on mountains, 2000 ft, May 1884, W. N. Suksdorf 15 (lectotype, designated by Jepson (1936: 67), NDG!; isolectotypes, GH!, NY!).
Arabis kochii Blankinship, Montana Coll. Agr. Sci. Stud. Biol. 1: 57. 1904. TYPE: United States, Montana, five syntypes not seen.
Arabis retrofracta var. multicaulis B. Boivin, Canad. Filed-Naturlist 63: 17. 1951. TYPE: Canada, Alberta, Jasper National Park, left bank of Malique River at Fish Hatchery, 14 Aug 1946, G. H. Turner 5086 (holotype, DAO!).
Plants short-lived perennials or biennials, with or without caudices, lacking crowded, persistent leaf bases; sexual, with ellipsoid pollen. Stems usually 1 per caudex branch, arising near ground surface from center of basal rosettes, 1.5–7.0(–10.5) dm, lower parts with abundant short-stalked, 2–8-rayed trichomes 0.1–0.2 mm, upper parts sparsely pubescent. Leaves at stem bases oblanceolate, 2–7 mm wide, entire or shallowly dentate, occasionally ciliate at petiole bases, blade surfaces densely pubescent with short-stalked, 5–10-rayed trichomes 0.05–0.2 mm; cauline leaves 15–40, concealing stem proximally, the uppermost pubescent, with auricles 0.5–2.5 mm or (very rarely) lacking. Inflorescences mostly unbranched, 15–80(–140)-flowered; fruiting pedicels 7–12(–18) mm, reflexed, abruptly recurved at base but otherwise usually straight, with appressed, branched trichomes. Flowers pendent at anthesis; sepals pubescent; petals white to lavender, 4–8 ´ 0.8–2.2 mm, glabrous; ovules 60–116 per fruit. Fruits 3.5–9.0 ´ 0.9–1.8 mm, strongly reflexed, usually appressed to rachises, occasionally somewhat secund, straight, with parallel edges, glabrous or sparsely pubescent throughout. Seeds uniseriate, 1.0–1.4 ´ 0.9–1.2 mm; wing continuous, to 0.1 mm. 2n = 14.
Habitat: rock outcrops, open hillsides, gravel bars and sandy banks in grassland, sagebrush, oak woodlands, and open conifer forests.
Elevation: 300–3250 m.
Distribution: Canada (Alberta, British Columbia, Manitoba, Northwest Territories, Ontario, Quebec, Saskatchwan), United States (Alaska, California, Idaho, Michigan, Montana, Nevada, Oregon, Utah, Washington, Wyoming).
Reproductive mode: sexual diploid.