Annuals [perennials], (10-)50-100[-250] cm. Leaves: petioles 20-40 mm; blades deltate or lanceolate to lance-linear overall, (30-)50-120(-220) × 10-50(-150) mm, sometimes either 1-pinnately lobed, primary lobes 3-5+, lanceolate to lance-linear, 30-120 × 3-25+ mm, or 2-pinnatisect, ultimate lobes linear, 5-30 × 1-2+ mm, bases truncate to cuneate, ultimate margins entire or serrate, seldom ciliate, apices obtuse to acuminate, faces glabrous or puberulent. Heads in ± corymbiform arrays. Peduncles (10-)40-60+ mm. Calyculi of 8-12(-17) usually erect, linear, seldom foliaceous bractlets 3-6 mm, margins ciliate, abaxial faces usually glabrous, sometimes hispidulous at bases. Involucres campanulate to hemispheric, 4-6 × 5-10 mm. Phyllaries 8-12, ovate to lanceolate, 4-5(-7) mm (margins usually yellow). Ray florets 5-6; laminae yellow, 10-30 mm. Disc florets 12-30(-60+); corollas yellowish, 3-4 mm. Cypselae dark brown to blackish, ± flattened, sometimes unequally 3-4-angled, ± linear, outer 4-6 mm, inner 5-7 mm, margins not barbed or ciliate, apices truncate, faces weakly 2-grooved, glabrous or sparsely strigillose, sometimes tuberculate; pappi 0, or of (1-)2(-4) erect to spreading, retrorsely barbed awns (1-)1.5-4 mm. 2n = 24 (Mexico). Flowering mostly Aug-Sep. Marshes, borders of streams, other wet sites; 900-2000 m; Ariz.; Mexico; Central America; introduced in Europe.

Plant: Perennial forb to 70 cm Leaves: lower leaves opposite, entire to dissected Flowers: heads rather showy, ray flowers yellow, 1cm long, disk flowers yellow Fruit: achenes narrow, linear; pappus of two retrorsely hispid awns.