Plants solitary or in clumps, not stoloniferous, with caudex or short-rhizomatous. Leaves basal and cauline, (basal persistent, cauline ± inconspicuous); petiole rounded, 2-20 mm; blade round to reniform, irregularly shallowly lobed, 20-80(-100) mm, thin, margins serrate, stipitate glandular-ciliate, apex obtuse to rounded, surfaces sparsely hairy. Inflorescences 30+-flowered, open, much-branched thyrses, usually some or all flowers replaced by bulbils (sometimes bulbils absent), 15-40 cm, dark purple-tipped stipitate-glandular; bracts (± inconspicuous), petiolate or sessile. Flowers: sepals reflexed (at least in fruit), ovate to elliptic, margins eciliate, surfaces sparsely stipitate-glandular or glabrous; petals white, not spotted, narrowly ovate to elliptic, (3-)4-6 mm, longer than sepals; filaments strongly club-shaped; ovary superior. 2n = 36, ca. 48, 50.

Flowering spring-summer. Moist to wet stream banks, mossy cliffs and slopes, waterfall spray zones; 0-2500 m; Alta., B.C.; Alaska, Calif., Idaho, Mont., Oreg., Wash.

Plants of Saxifraga mertensiana bear bulbils in the axils of basal leaves.