Annuals or, rarely, biennials; (terrestrial or of wet habitat, not submerged); glabrous or hirsute. Stems (simple or few- to many-branched from base), decumbent or erect, branched distally, 1-4(-5.5) dm, (hirsute proximally). Basal leaves rosulate; blade margins pinnatifid. Cauline leaves shortly petiolate or sessile; blade oblong to oblanceolate, (lateral lobes oblong to ovate), (3.5-) 4.5-9(-12) cm × 10-25(-33) mm, (lateral lobes smaller than terminal), base auriculate or not, margins pinnatifid to pinnatisect, or (lateral lobes) crenate to subentire. Racemes elongated. Fruiting pedicels divaricate to slightly reflexed, straight or recurved, 1.5-3.7(-4.3) mm. Flowers: sepals ascending, oblong to ovate, 0.7-1.3 × 0.4-0.7 mm; petals yellow, oblanceolate to spatulate, 0.6-1.2 × 0.2-0.5 mm; median filaments 0.9-1.2 mm; anthers ovate, 0.2-0.3 mm. Fruits silicles, straight, globose or subglobose, 1.2-2.5(-3) mm diam.; valves glabrous; ovules 20-42 per ovary; style 0.1-0.7(-1) mm. Seeds biseriate, brown, cordiform, 0.5-0.7 mm, finely colliculate. Flowering May-Aug. Shores of ponds and lakes, mud flats, stream edges, moist grounds; 1200-3300 m; Ariz., Calif., Colo., Idaho, N.Mex., Tex., Utah, Wyo.; Mexico (Chihuahua).

Plant: annual; stem decumbent to erect, 1-4 dm; branches 0 or from base; hairs below, sparse Leaves: petioled to sessile, 4-10 cm, oblanceolate, deeply ± pinnately lobed; lobes dentate; cauline reduced upward INFLORESCENCE: racemes, terminal and lateral Flowers: bisexual; sepals 4, free; petals (0)4, free, 0.5-1 mm, oblong to narrowly spoon-shaped, yellow; stamens generally (2,4)6, generally 4 long, 2 short; ovary 1, superior, chambers generally 2, septum membranous, connecting 2 parietal placentas, style 1, stigma simple or 2-lobed Fruit: capsule with 2 or 4 deciduous valves, 1-2.5 mm, ± round; pedicel spreading to recurved, 1.5-4 mm, slender; style 0.2-1 mm; Seed 0.5-0.7 mm, widely reniform, 0-200, (1)2 rows per chamber, dense, generally plump; wing 0; embryonic root at edges of both cotyledons Misc: Lake margins, muddy streambanks; 1200-2450 m.