38. Boechera gracilenta (Greene) Windham & Al-Shehbaz, Harvard Pap. Bot. 12: 240. 2007; Arabis gracilenta Greene, Pittonia 4: 194. 1900. TYPE: United States, New Mexico, Santa Fe Co., canyon, 1 mile SE of Santa Fe, 7400 ft, 21 May 1897, A. A. Heller & E. G. Heller 3562 (holotype, NDG!; isotype, GH!, NY!).
Arabis selbyi Rydberg, Bull. Torrey Bot. Club 31: 557. 1904; Boechera selbyi (Rydberg) W. A. Weber, Phytologia 51: 371. 1982. TYPE: U.S.A. Colorado. Ouray Co.: canyons and adjoining meadows, west of Ouray, 2300–2800 m, 9 Sep 1901, L. M. Underwood & A. D. Selby 207 (holotype, NY!).
Arabis perennans var. thorneae S. L. Welsh, Utah Fl., ed. 3. 259. 2003; Boechera selbyi var. thorneae (S. L. Welsh) N. Holmgren, Brittonia 56: 246. 2004. Uintah: Green River Formation, Mahogany Member, Threemile Creek Road, 1.7 mile E of landing strip, T12S, R25E, S8, 6290 ft., 27 May 1982, K. Thorne, B. Neely & C. Fulmer 1832 (holotype, BRY).
Plants short- or (rarely) long-lived perennials, with mostly non-woody caudices, lacking crowded, persistent leaf bases; apomictic, with spheroid pollen. Stems 1–9 per caudex branch, arising near ground surface from margin or center of basal rosettes, (1.5–)2.5–5.5 dm, lower parts with many short-stalked, 2–4-rayed trichomes 0.1–0.5 mm and a few simple trichomes to 0.8 mm, upper parts glabrous. Leaves at stem bases oblanceolate, 2–9 mm wide, shallowly dentate or occasionally entire, ciliate proximally with simple and spurred trichomes to 1.2 mm, blade surfaces moderately to densely pubescent with short-stalked, 4–6(–8)-rayed trichomes 0.1–0.5 mm; cauline leaves 4–9, not concealing stem, the uppermost usually glabrous, with auricles 1–3 mm. Inflorescences mostly unbranched, 7–20-flowered; fruiting pedicels (7–)10–18 mm, divaricate-ascending, gently curved downward, glabrous. Flowers ascending at anthesis; sepals pubescent; petals lavender, 6–7 ´ 1.5–2.0 mm, glabrous; ovules 60–96 per fruit. Fruits (3.0–)4.5–7.0 cm ´ 1.7–2.0 mm, widely pendent or rarely horizontal, not appressed to rachises, not secund, slightly curved, with parallel edges, glabrous; style 0.1–0.3 mm. Seeds subbiseriate, 1.2–1.8 ´ 0.9–1.2 mm; wing continuous, 0.1–0.25 mm wide.
Habitat: rocky slopes and sandy soil in pinyon-juniper woodland and mountain shrub communities.
Elevation: 1900–2300 m.
Distribution: United States (Arizona, Colorado, New Mexico, Utah).
Reproductive mode: apomictic triploid.