Plants in groups or sometimes almost mat-forming, with bulbils on caudices or rhizomatous. Leaves basal; petiole flattened, 1-5 cm; blade ovate to elliptic, 1.5-3.5 cm, ± fleshy, base ± attenuate to ± truncate, margins shallowly, sharply serrate, ciliate, surfaces sparsely tangled, reddish brown-hairy abaxially, glabrous adaxially. Inflorescences usually (10-)30+-flowered, flowers crowded into 1+ glomerules in thyrses with ascending branches, 8-30 cm, purple-tipped stipitate-glandular; (bracts glabrous or marginally glandular-ciliate). Flowers: sepals ascending to spreading, sometimes reflexed in fruit, ovate to oblong, (surfaces glabrous); petals white, not spotted (spots rarely present), obovate to almost round, clawed, 2-4 mm, to 1.5 times as long as sepals; filaments linear to very slightly widened near anthers, flattened; pistils distinct almost to base; ovary ± superior. Capsules greenish or reddish to ± dark purple, folliclelike. 2n = 20, 38, 40, 56, 58. Flowering spring-summer. Wet, rocky or gravelly slopes, moist to dry alpine meadows, flushes; 500-4000 m; Alta., B.C., Sask.; Alaska, Idaho, Mont., Nev., Oreg., S.Dak., Wash., Wyo. Micranthes occidentalis appears closely related to the little-known M. mexicana (Engler & Irmscher) Brouillet & Gornall from Chihuahua, Mexico. The latter is the only species of the genus that occurs in Mexico and not in the United States. Micranthes occidentalis is disjunct between the northern Rocky Mountains and the Cypress Hills of southeastern Alberta and southwestern Saskatchewan, and the Black Hills of South Dakota. It hybridizes with M. idahoensis where their ranges overlap.