Fl. Bor.-Amer. 2: 141. 1838. (as setigerum)
Herbs, annual, 0.5–5 dm, monoecious. Stems densely and dichotomously shortly branched, forming loose, prostrate circular mats 5–80 cm across, proximally bristly stellate-hairy, central radii spreading, 2–3 mm. Leaves mostly clustered near inflorescences; stipules rudimentary; petiole 0.3–5 cm, glands absent at apex; blade ovate to rhombic, 0.8–6.5 × 0.8–4 cm, base cuneate, margins entire, apex obtuse, abaxial surface pale grayish green, adaxial surface grayish green, both densely stellate-hairy. Inflorescences unisexual; staminate dense capitate clusters, 1–2 cm, flowers 2–10; pistillate clusters, 1–2 cm, flowers 1–3. Pedicels: staminate 0–1 mm, pistillate absent. Staminate flowers: sepals 5–6, 2–2.5 mm, abaxial surface densely stellate-hairy; petals 0; stamens 5–9. Pistillate flowers: sepals 0; petals 0; ovary 1-locular; style 1, 2–3 mm, unbranched. Capsules follicular (1-seeded), 3–6 × 2–3 mm, smooth; columella absent. Seeds 3–5 × 2–3 mm, shiny. 2n = 20.
Phenology: Flowering Jun–Oct.
Habitat: Coastal sage scrub, foothill woodlands, valley grasslands, oak woodlands, edges of fields, dry stream beds, disturbed areas, roadsides.
Elevation: 0–1900 m.
Ariz., Calif., Idaho, Nev., Oreg., Utah, Wash., Mexico (Baja California), introduced s South America (Chile), Australia.
Croton setigerus is nearly unique in the genus with its one-locular fruit, single unbranched style, and pistillate flowers devoid of any perianth. The foliage is toxic to animals, and the crushed plants were used by Native Americans to stupefy fish. The seeds are palatable to birds, giving rise to the common names cited above. Individual plants produce either mottled, striped, or solid gray or black seeds. Gray seeds are produced by desiccating plants and appear to be much less palatable to doves than the other color morphs (A. D. Cook et al. 1971).