Stems erect or ascending, rooting at most proximal nodes, glabrous. Roots not thickened basally, glabrous. Proximal cauline leaf blades ovate or lanceolate, 1.2-4.2 × 0.5-1.2 cm, base acute to truncate, margins entire or denticulate, apex acuminate to rounded. Inflorescences: bracts linear to lanceolate or oblanceolate. Flowers: receptacle glabrous; sepals 4-5, spreading or reflexed from base, 1.5-3 × 1-1.5 mm, glabrous or sparsely hirsute; petals 1-3, 1.5-2 × 0.5-1 mm; nectary scales glabrous. Heads of achenes hemispheric to cylindric, 2-8 × 2-3 mm; achenes 1-1.2 × 0.6-0.8 mm, ± tuberculate, glabrous; beak absent or nearly so, to 0.1 mm.

Flowering spring (Apr-Jun). Ditches, ponds, and swamps; 0-300 m; Ala., Ark., Calif., Del., D.C., Fla., Ga., Ill., Ind., Ky., La., Md., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va.

In most specimens of Ranunculus pusillus , the heads of achenes are hemispheric to short-ovate and only 2-3 mm. Occasional plants with cylindric heads of achenes 4-6 mm from the Gulf Coast states have been called R . pusillus var. angustifolius .

Annual; stems weak, ascending or erect, 1-5 dm, branched from the base, many-fld; lower lvs long-petioled, ovate or lance-ovate, 1-4 cm, basally obtuse or rounded; cauline lvs progressively narrower, most of them linear, scarcely differentiated into blade and petiole; pet 1-5, 2 mm, equaling or a little shorter than the sep; stamens 10 or fewer; achenes 1 mm, very shortly beaked. Ditches, muddy ground, and shallow water, mostly on the coastal plain; s. N.Y. to Fla. and Tex., n. in the interior to Mo., Ind., and O. May, June.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

©The New York Botanical Garden. All rights reserved. Used by permission.

[Deam divides this complex into two species: R. pusillus sensu stricto and R. oblongifolius. His R. pusillus is a glabrous plant with smaller flowers. Ranunculus pusillus sensu stricto] was reported from Knox County by Spillman. I found a large colony of it in a low woods about a mile east of Palmyra in Harrison County, and it is a common plant surrounding a pond of about 2 acres nearly 2 miles southeast of Palmyra. It has also been found by Edna Banta in Jefferson County. [Regarding the more robust form, R. oblongifolius, Deam says:] I found this species to be frequent in a low, open woods in the Hunley Bottoms about a mile northeast of Huntingburg in Dubois County, and in three widely separated places in Posey County where it was common in hard, white clay soil in very wet, fallow fields. Winona Welch collected it in Graebert's woods about 8 miles southwest of Mt. Vernon in Posey County, and Edna Banta found it in the "flats" in Jefferson County.