Annuals or, rarely, biennials; puberulent, at least proximally, or glabrous, (some trichomes clavate to hemispherical, vesicular). Stems (simple or several from base), usually prostrate or decumbent, rarely erect, branched distally, 1-4 dm, (glabrous or pubescent, trichomes vesicular). Basal leaves rosulate; blade margins pinnatifid. Cauline leaves shortly petiolate; blade oblong, oblanceolate to obovate, or lyrate-pinnatisect, (lateral lobes oblong to ovate), (2-)3.5-10(-13.5) cm × 10-40(-53) mm, base auriculate or not, margins usually pinnatifid to pinnatisect, rarely 2-pinnatifid, (lateral lobes) dentate to crenate or sinuate, (surfaces glabrous or adaxially pubescent, trichomes vesicular). Racemes elongated. Fruiting pedicels ascending to horizontal, straight or curved-ascending, (1.5-)2.3-4.7(-5.3) mm. Flowers: sepals erect, oblong, 1.5-2.5 × 0.5-1 mm; petals yellow, spatulate, 1-2 × 0.4-0.7 mm; median filaments 1.2-1.7 mm; anthers ovate, 0.2-0.3 mm. Fruits siliques, straight or curved, linear to oblong-linear, 8-14(-21) × 1-2.5 mm; valves glabrous or pubescent; ovules (100-)150-210 per ovary; style (0.2-)0.5-1.1 mm. Seeds biseriate, reddish brown, cordiform, 0.4-0.5 mm, foveolate.
Flowering Dec-May. Wet areas, muddy grounds, edges of canals and ditches, sandy fields, margins of ponds, streamsides, peat; 0-600 m; Ala., Ark., Fla., Ga., La., Miss., N.C., Okla., S.C., Tex.; Mexico; Central America (Honduras, Nicaragua).
A sp. chiefly of the coastal plain of s. U.S. and s. to Mex., extends up the Mississippi embayment occasionally as far as St. Louis. It would key to R. sessiliflora, from which it differs in having short but evident pet 1-2 mm, fewer (mostly 100-150) seeds, an often longer style (to 1.5 mm), and in often being provided with vesicular trichomes.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.