Perennials; usually glabrous. Rhizomes often elongated, usually slender, rarely thickened, 1-2(-5) mm diam., (not fleshy). Stems (simple or few to several from base), erect to ascending, (not flexuous), unbranched basally, sometimes branched distally, (0.3-)0.8-2.5(-3) dm. Basal leaves (sometimes withered by anthesis), rosulate, pinnately compound, (3 or) 5 or 7 (or 9)-foliolate, 2-5 (-9) cm, leaflets petiolulate or subsessile; lateral leaflets shortly petiolulate or subsessile, blade usually broadly ovate, rarely broadly obovate or orbicular, smaller than terminal, margins usually entire, rarely slightly 3 (or 5)-lobed or crenate; terminal leaflet subsessile, blade reniform or orbicular, 0.4-0.8(-1.2) cm × 5-9(-16) mm, margins entire or 3 (or 5)-lobed or crenate. Cauline leaves 3-5(-7), 3-7 (or 9)-foliolate, petiolate, leaflets subsessile or sessile; base not auriculate; lateral leaflets: blade narrowly obovate, oblanceolate to linear, margins similar to terminal; terminal leaflet blade narrowly obovate, ovate, oblanceolate, lanceolate, oblong, margins usually entire, sometimes 3-lobed or crenate. Racemes ebracteate, (subumbellate, 2-8(-14)-flowered, rachis usually 3-20 mm). Fruiting pedicels suberect to ascending, 3-8(-10) mm. Flowers: sepals (greenish or purplish), oblong, 1-2 × 0.5-1 mm, lateral pair not saccate basally; petals white, narrowly obovate, 2.5-5 × 1-3 mm. Fruits linear, (torulose), (1.3-)1.8-2.5(-3) cm × 0.8-1.5(-2) mm; (valves glabrous or sparsely pubescent); style 0.5-2 mm. Seeds brown, oblong, 1-1.5 × 0.8-1 mm. 2n = 32, 36, 48. Flowering Jun-Sep. Stream banks, tundra, alpine slopes, wetlands, damp, swampy and mossy areas, beach gravel and sand, alpine stream margins; 0-1800 m; Alta., B.C., N.W.T., Yukon; Alaska, Wash.; e Asia (Russian Far East). Recent molecular data (J. Lihová et al. 2006) indicate that Cardamine umbellata, often treated as a variety of C. oligosperma, represents a distinct lineage more closely related to taxa from New Zealand; this does not exclude C. oligosperma as one of the possible parents of this polyploid.
