Annuals, 50-200 cm. Stems single, branches ascending or spreading, glabrous. Leaves withered at flowering (glabrous). basal blades linear to oblanceolate, runcinate. 3-10 cm, margins pinnately lobed. cauline much reduced, bractlike . Heads borne singly or clustered along branches . Peduncles 3-4 mm. Calyculi of reflexed bractlets. Involucres 7-9 mm (sparsely glandular-puberulent). Florets 11-13. Cypselae light tan to brown, 1.9-2.3 mm, faces smooth, slightly bumpy or tuberculate, grooved; pappi of 19-21, white bristles (falling), plumose on distal 80-85%. 2n = 16.
Flowering Aug-Nov. Open, pioneer sites such as old clearings, sand dunes, coastal sage communities, chaparral openings, and sandy roadside embankments; 20-600 m; Calif.; Mexico (Baja California).
The morphologic characteristics of Stephanomeria diegensis are a combination of those of S. exigua and S. virgata, and the species is thought to have evolved from genetic segregates of their hybridization (L. D. Gottlieb 1971; G. P. Gallez and Gottlieb 1982).