Annuals; densely hispid at least proximally. Stems erect, branched distally, (2-)3.5-12 (-17.5) dm, often densely hispid proximally, (trichomes retrorse), usually glabrous distally. Basal leaves rosulate; petiole 1-4(-5) cm; blade broadly oblanceolate (in outline), (1.5-)2.5-8(-12) cm × (10-)20-50(-70) mm, margins runcinate to lyrate-pinnatifid; lobes 2-4 on each side, much smaller than terminal lobe, margins entire or dentate, (terminal lobe triangular, often hastate). Cauline leaves similar to basal; blade (much smaller than basal, to 1.5 cm wide), margins entire or toothed. Fruiting pedicels divaricate or ascending, slender, narrower than fruit, 5-12(-15) mm. Flowers: sepals ascending, oblong, 3-4 × 1-1.5 mm; petals spatulate, 6-8 × 2-3 mm, claw 2.5-3.5 mm; filaments 3-4.5 mm; anthers ovate, 0.6-1 mm. Fruits (ascending to suberect, young fruits not overtopping flowers), narrowly linear, curved or straight, subtorulose, slender, 2-3.5(-5) cm × 0.9-1.1 mm; valves often glabrous; ovules 40-60 per ovary; style stout, 0.3-0.7 mm; stigma prominently 2-lobed. Seeds 0.7-1 × 0.5-0.6 mm. 2n = 14.

Flowering late May-early Nov. Valleys, stream banks, fields, roadsides, pastures, waste grounds, vacant lots, prairies, disturbed sites, railroad tracks; 0-2400 m; introduced; Alta., B.C., Man., N.B., Que., Sask.; Colo., Conn., Idaho, Ill., Ind., Iowa, Mass., Mich., Mont., Nebr., Nev., N.Mex., N.Dak., Ohio, Oreg., Pa., S.Dak., Utah, Vt., Wash., Wyo.; e Europe; w, c Asia.