Annuals; (terrestrial or of wet habitat, not submerged); glabrous throughout. Stems (several-branched from base), prostrate to decumbent, branched distally, 0.7-3.5 (-4) dm. Basal leaves not rosulate; blade margins pinnatifid. Cauline leaves shortly petiolate, or (distal) sessile; blade oblong to oblanceolate or lanceolate, (lateral lobes linear, oblong to ovate, or obovate), 2-9(-11) cm × 7-20(-30) mm, (lateral lobes smaller than terminal), base not auriculate, margins pinnatifid, or (lateral lobes) entire, dentate, or sinuate. Racemes elongated. Fruiting pedicels ascending to divaricate, (1-)1.5-3.2(-4.2) mm, straight. Flowers: sepals ascending, oblong, 0.7-1.3 × 0.4-0.7 mm; petals yellow, oblong to oblanceolate or spatulate, 0.5-0.8 × 0.1-0.3 mm; median filaments 0.8-1.2 mm; anthers ovate, 0.1-0.2 mm. Fruits siliques or silicles, curved-ascending, lanceolate to narrowly ovoid or oblong-lanceolate, 3-7(-9) × (0.8-) 1-1.7(-2) mm (often slightly constricted at middle); valves papillate; ovules 20-80 per ovary; style (0.2-) 0.5-1 mm. Seeds biseriate, reddish brown, cordiform, 0.5-0.7 mm, colliculate. Flowering Jun-Oct. Shores of lakes and ponds, mud flats, marshes, sand bars, moist grounds, streamsides; 1300-3000 m; Alta., B.C., Sask.; Calif., Colo., Idaho, Mo., Mont., Nebr., Nev., N.Mex., N.Dak., Oreg., S.Dak., Tex., Utah, Wash., Wyo.; Mexico (Baja California, Chihuahua).