Annuals, 5-70 cm (sometimes acaulescent, glabrous or lightly farinose, usually white-villous proximally); taprooted. Stems 1-5+, erect, sometimes well branched proximally (internodes 0.3-6 cm, or plants acaulescent). Leaves all or mostly basal; obscurely petiolate; blades (often reddish or purplish), linear or narrowly lanceolate, (bases ± clasping) margins entire or remotely, pinnately lobed or dentate (white-villous-ciliate proximally, apices acuminate, faces glabrous or crisped white-villous throughout). Heads borne singly (erect). Peduncles (erect from bud to mature fruit) inflated distally, ebracteate. Calyculi 0. Involucres fusiform to ovoid, 3-15 mm diam. Phyllaries 5-26 in 3-4 series, lanceolate, unequal (outer shorter, inner equal), margins scarious, apices long-tapering, acute, faces glabrous. Receptacles flat or convex, pitted, glabrous, epaleate. Florets 5-150. corollas pale yellow, usually reddish abaxially. Cypselae usually black or dark brown. rarely gray (outer sometimes paler), ± columnar to fusiform, often narrowed distally to relatively short beaks, ribs 10, minutely scabrous, hispidulous; pappi falling, of 5, distinct. white, lustrous, lanceolate, aristate scales (apices notched, aristae smooth). x = 9. Uropappus lindleyi was placed in Microseris (K. L. Chambers 1955) because of two allotetraploid species formed by hybridization with annual members of that genus. A number of morphologic features, including narrow, acuminate leaves with villous-ciliate margins, erect heads, relatively long outer phyllaries, cypselae often short-beaked, and pappi of white, lustrous scales suggest a connection with Nothocalaïs, especially N. troximoides. Phylogenetic studies of chloroplast DNA variation (R. K. Jansen et al. 1991b; J. Whitton et al. 1995) link Uropappus with Nothocalaïs and Agoseris as a sister clade to Microseris. Consequently, Jansen et al. separated Uropappus from Microseris and placed the two allotetraploid species in Stebbinsoseris.