10. Boechera cascadensis Windham & Al-Shehbaz, Harvard Pap. Bot. 11: 260. 2007.
Arabis microphylla Nuttall var. thompsonii Rollins, Rhodora 43: 429. 1941, not Boechera thompsonii (S. L. Welsh) N. H. Holmgren 2005
Perennials; long-lived; (ces-pitose); apomictic; caudex somewhat woody. Stems usually 1 per caudex branch, arising from center of rosette near ground surface, 0.5-2.2 dm, sparsely pubescent proximally, trichomes simple and short-stalked, 2- or 3-rayed, 0.1-0.2 mm, glabrous distally. Basal leaves: blade linear-oblanceolate, 0.7-2 mm wide, margins entire, ciliate proximally, trichomes to 0.4 mm, surfaces densely pubescent, trichomes short-stalked, (2- or) 3-6-rayed, 0.05-0.2(-0.3) mm. Cauline leaves: 4-6, not concealing stem; blade auricles 0.5-1 mm, surfaces of distalmost leaves glabrous. Racemes 3-11-flowered, unbranched. Fruiting pedicels ascending to divaricate-ascending, straight, 3-8 mm, glabrous. Flowers ascending at anthesis; sepals glabrous or sparsely pubescent; petals lavender, 5-6 × 1-1.7 mm, glabrous; pollen spheroid. Fruits ascending to divaricate-ascending, not appressed to rachis, not secund, straight, edges parallel, 3.5-6.2 cm × 1.2-1.5 mm; valves glabrous; ovules 58-80 per ovary; style 0.8-1.5 mm. Seeds uniseriate, 1.1-1.3 × 0.9-1 mm; wing continuous, 0.05-0.1 mm wide.
Flowering Jun. Basaltic cliffs and rocky slopes in subalpine areas; of conservation concern; ca. 1900 m; Oreg., Wash.
Morphological evidence suggests that Boechera cascadensis is an apomictic species that arose through hybridization between B. microphylla and B. paupercula (see M. D. Windham and I. A. Al-Shehbaz 2007 for detailed comparison). It is known from two collections: the type specimens from Kittitas County, Washington, and a more recent collection from Baker County, Oregon.