66. Boechera pauciflora (Nuttall) Windham & Al-Shehbaz, Harvard Pap. Bot. 11: 268. 2007.
Sisymbrium pauciflorum Nuttall in J. Torrey and A. Gray, Fl. N. Amer. 1: 93. 1838; Arabis arcuata (Nuttall) A. Gray var. subvillosa S. Watson; A. columbiana Macoun; A. perelegans A. Nelson; A. sparsiflora Nuttall var. columbiana (Macoun) Rollins; A. sparsiflora var. subvillosa (S. Watson) Rollins; Boechera sparsiflora (Nuttall) Dorn var. subvillosa (S. Watson) Dorn
Perennials; short- to long-lived; apomictic; caudex sometimes woody. Stems usually 1 per caudex branch, arising from center of rosette near ground surface, (1.4-) 3-11.2 dm, densely pubescent proximally, trichomes simple, 0.6-1.5 mm, mixed with stalked, 2- (or 3-)rayed ones, 0.2-0.4 mm, sparsely pubescent distally. Basal leaves: blade oblanceolate, 3-10 mm wide, margins usually dentate, rarely entire, sometimes ciliate, trichomes (simple or branched), to 1 mm, surfaces densely pubescent, trichomes stalked, 2-5-rayed, 0.3-0.6 mm. Cauline leaves: (8-)14-60, often concealing stem proximally; blade auricles (1-)3-10 mm, surfaces of distalmost leaves glabrous or sparsely pubescent. Racemes 17-60-flowered, usually unbranched. Fruiting pedicels horizontal to divaricate-descending, usually straight, rarely slightly recurved, 4-13 mm, pubescent, trichomes spreading, 2- or 3-rayed. Flowers divaricate at anthesis; sepals pubescent; petals lavender to whitish, 5-8 × 1-2 mm, glabrous; pollen spheroid. Fruits horizontal, divaricate-descending or widely pendent, not appressed to rachis, not secund, curved, edges parallel, 5.5-10.5 cm × 1.5-2.2 mm; valves glabrous; ovules 80-162 per ovary; style 0.05-0.5 mm. Seeds uniseriate, 1.4-1.8 × 1-1.4 mm; wing continuous, 0.1-0.25 mm wide. 2n = 21.
Flowering May-Jun. Rocky soil in sagebrush areas, mountain shrub communities, edges of conifer forests; 600-2500 m; B.C.; Calif., Idaho, Mont., Nev., Oreg., Utah, Wash., Wyo.
Morphological evidence suggests that Boechera pauciflora is an apomictic species that arose through hybridization between B. retrofracta and B. sparsiflora. Specimens of B. pauciflora are commonly identified as Arabis holboellii var. pinetorum (= B. pinetorum), a superficially similar species restricted to the northern Sierra Nevada and southern Cascade Range (see M. D. Windham and I. A. 2007 for detailed comparison).
Arabis elegans A. Nelson (1900), not Tineo & Lojacono (1886) is an illegitimate name, sometimes found in synonymy with Boechera pauciflora.