7. Boechera calderi (G. A. Mulligan) Windham & Al-Shehbaz, Harvard Pap. Bot. 11: 259. 2007.
Arabis calderi G. A. Mulligan, Rhodora 97: 144, fig. 4. 1996
Perennials; usually short-lived; apomictic; caudex not woody. Stems usually 1 per caudex branch, arising from center of rosette near ground surface, 1-4.5 dm, glabrous throughout. Basal leaves: blade oblanceolate, 1.5-6 mm wide, margins entire, ciliate at petiole base, trichomes to 0.8 mm, surfaces sparsely pubescent, trichomes sessile, malpighiaceous (usually at margin) and 3- or 4-rayed, 0.15-0.4 mm. Cauline leaves: 5-17, often concealing stem proximally; blade auricles 1-3 mm, surfaces of distalmost leaves glabrous. Racemes 10-25-flowered, unbranched. Fruiting pedicels erect, straight, 5-10 mm, glabrous. Flowers erect at anthesis; sepals glabrous; petals purple, 6-9 × 1.5-2.5 mm, glabrous; pollen spheroid. Fruits erect, appressed to rachis, not secund, straight, edges parallel, 3.5-6.5 cm × 1.8-2.5 mm; valves glabrous; ovules 64-134 per ovary; style 0-0.2 mm. Seeds biseriate to sub-biseriate, 1.8-2.2 × 1-1.8 mm; wing continuous, 0.2-0.5 mm wide.
Flowering Jun-Aug. Exposed rocky ridges, meadows, open forests near timberline; 1500-3500 m; Alta., B.C., N.W.T., Yukon; Calif., Idaho, Mont., Oreg., Wash., Wyo.
Morphological evidence suggests that Boechera calderi is an apomictic species that arose through hybridization between B. lyallii and B. stricta (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison).