Stems erect or ascending, rooting at proximal nodes, glabrous or sparsely hirsute. Roots not thickened basally, glabrous or somewhat canescent proximally. Proximal cauline leaf blades lanceolate, 5.9-12.2 × 1.1-2.4 cm, base rounded-obtuse to acuminate, margins denticulate, apex acuminate. Inflorescences: bracts linear or lanceolate. Flowers: receptacle glabrous; sepals 5, spreading or sometimes reflexed from base, 3-5 × 2-3 mm, glabrous; petals 5, 5-8 × 2-3 mm; nectary scales glabrous. Heads of achenes short-ovoid to depressed-globose, 5-7 × 4-8 mm; achenes 1.8 × 1.2-1.4 mm, glabrous; beak lanceolate, straight, 0.6-1.2 mm. Flowering late spring-summer (May-Aug). Creeks, ponds, ditches, marshes; 0-700 m; Ala., Conn., Del., D.C., Ga., Ill., Ind., Ky., La., Maine, Md., Mass., Mich., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., Tenn., Va., W.Va. The name Ranunculus obtusiusculus Rafinesque has been mistakenly used for R . ambigens .