Found in springy places about lakes, along streams and ditches, infrequent in swamps and ponds in woodland, and in the outlets of springs. It requires fresh water which is more or less circulating. It is frequent in the lake area, becoming less frequent to very local southward. The leaves, both basal and cauline, vary much in the width of the basal sinus and in the margins. Some have a very wide sinus while others have a narrow one. The margins vary from almost entire to acutely dentate. Nieuwland (Amer. Midland Nat. 3: 325. 1914) describes a form found in Porter County with "the upper leaves under the inflorescence somewhat lobed not unlike those of the red maple, the leaves were laciniately toothed." Hansen reported Caltha flabellifolia from Kosciusko County. I am referring this report to Caltha palustris. See excluded species no. 230, p. 1047.
Stems hollow, 2-6 dm, branched above; basal lvs long-petioled, the broadly cordate-rotund blade usually with a deep and narrow sinus; cauline lvs with progressively shorter petiole and wider sinus; fls bright yellow, 1.5-4 cm wide; stamens 50-120; anthers linear-oblong or lance- oblong, 2 mm; follicles 4-15, 10-15 mm; 2n=32. Wet woods and meadows, swamps, bogs, and shallow water; circumboreal, s. to Va., W.Va., Ind., Ill., and Io., and in the mts. to N.C. and Tenn. Apr.-June. Forms with the basal leaves somewhat flabellate, with a relatively broad and open sinus, do not appear to be taxonomically separable. (var. flabellifolia)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.