Reise 3: 284. 1776.
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. 2n=16, 32.
Phenology: Flowering late spring–summer (Jun–Aug).
Habitat: Floating or on moist mud, ponds, lakes, slow-moving rivers and streams
Elevation: 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.
"thick" is not a number.