19. Saxifraga debilis Engelmann ex A. Gray, Proc. Acad. Nat. Sci. Philadelphia. 15: 62. 1864.
Saxifraga cernua Linnaeus var. debilis (Engelmann ex A. Gray) Engler; S. hyperborea R. Brown subsp. debilis (Engelmann ex A. Gray) Á. Löve, D. Löve & B. M. Kapoor; S. rivularis Linnaeus var. debilis (Engelmann ex A. Gray) Dorn
Plants usually densely tufted, sometimes loosely so, not stoloniferous, not rhizomatous. Leaves basal and cauline, (3-5, proximal similar to basal); petiole ± flattened, 5-70 mm; blade round or reniform, (3-)5-7-lobed (lobes obtuse), (3-)4.5-6.7(-10.3) mm, slightly fleshy, margins entire, eciliate, surfaces glabrous. Inflorescences 2-3(-5)-flowered, capitate cymes, sometimes solitary flowers, (flowers subsessile), (3-)6.7-9(-19.4) cm, tangled, nonglandular-hairy; bracts petiolate. Flowers (hypanthium V-shaped in longisection, glabrous or sparsely short stipitate-glandular); sepals erect, oblong to ovate, (0.7-1 mm wide), margins eciliate, surfaces abaxially glabrous; petals white to pale purple, not spotted, oblong, (1.7-)3-4.4(-6.2) mm, ± equaling sepals; ovary 1/2 inferior. 2n = 26.
Flowering summer. Alpine meadows, snow beds, open gravel and silt, seepage areas, stream and lake margins, shady taluses, ravines or cliffs; 2500-4000 m; Colo., Mont., N.Mex., Utah, Wyo.
Saxifraga debilis is known only from the central and southern Rocky Mountains, where it is often called S. rivularis (a species not present in the area). Its V-shaped (in longisection), glabrous or sparsely short stipitate-glandular hypanthia, and larger, more-lobed leaves (similar to S. bracteata in this) distinguish it from S. hyperborea, which is sometimes sympatric (M. H. Jørgensen et al. 2006).