Stems 0 or 1 (internodes much shorter than subtending leaves). Leaves erect to spreading; blades (1-)3-15(-23) cm × (0.5-)2-10(-16) mm, mostly toothed, rarely lobed, lobes or teeth in 2-3 pairs, faces glabrous or densely, ± uniformly hairy. Peduncles 6-53 cm, lengths mostly (0.5-)1.5-4.5 times leaves at flowering, (1.5-)2-5 times leaves in fruit, glabrous or glabrate, or apically puberulent to villous. Heads 2-10(-12) mm wide at flowering. Phyllaries green or medially rosy purple, sometimes spotted, margins glabrous or ciliate, faces mostly hairy, occasionally glabrous, or villous, stipitate-glandular, translucent, yellowish or purple-septate and often purple-tipped trichomes, or eglandular with whitish opaque trichomes; outer erect to spreading, adaxially glabrous or puberulent and eglandular. Florets (5-)20-50(-100); corollas ± equaling phyllaries at flowering, tubes 1-4 mm, ligules 2-6 × 1-2 mm; anthers 1-1.5 mm. Cypselae: outermost strongly differing from inner, highly variable in color, shape, ornamentation, and pubescence; ribs flattened to alate, or 0, straight to strongly undulate, not diminishing proximally. 2n = 18, 36.

Flowering Mar-Sep. Wet to dry, mostly seasonal habitats in deserts, grasslands, chaparral, steppe, oak woodlands, and open pine forests, often disturbed sites; 0-2300 m; B.C.; Ariz., Calif., Idaho, Mont., Nev., N.Mex., Oreg., Utah, Wash.; Mexico (Baja California, Guadalupe Island); introduced, Europe (Sweden).

Variety heterophylla is the most widespread of the varieties. It exhibits remarkable variation in cypsela morphology. K. L. Chambers (1963b) demonstrated that this small-flowered variety is strongly autogamous and does not outcross. The same breeding system may be present in other Agoseris taxa that exhibit reduced corolla and anther size (e.g., A. apargioides var. maritima, A. grandiflora, A. aurantiaca). Hybridization does not appear to be common; apparent intermediates with A. apargioides and A. hirsuta are known.