Stems leafy, floating or creeping, rooting at nodes. Basal leaves: blade ovate-reniform or cordate, largest 1-2.5 × 1-5 cm, margins nearly entire. Inflorescences 2-6-flowered. Flowers 8-13 mm diam.; sepals white or pinkish, 4-7(-8) mm. Follicles 20-55, widely spreading, sessile, oblong; bodies 3.2-6.5 × 1-2.5 mm; style and stigma curved, 0.1-0.4 mm. Seeds broadly elliptic, 0.5-0.8 mm. 2 n =16, 32. Flowering late spring-summer (Jun-Aug). Floating or on moist mud, ponds, lakes, slow-moving rivers and streams; 25-1500 m; Alta., B.C., Man., N.W.T., Ont., Sask., Yukon; Alaska, Minn., Wis.; Eurasia. Unlike the other species of Caltha in North America, C . natans is relatively invariable morphologically and has not been divided into segregate taxa.
Stems slender, floating; lvs reniform to broadly cordate, 2-5 cm; fls pink or white, 1 cm wide; stamens 12-25; anthers subrotund, 0.5 mm; follicles 20-40, in a dense head, 4-5 mm; 2n=32. Ponds or slowly flowing streams; circumboreal, s. to n. Wis. and n. Minn. July, Aug.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.