Subshrubs, to 16 cm (rounded or flat-topped). Stems greenish to gray, much branched, pilose. Leaf blades 1-nerved, linear to acerose, 8–20 × 1–2 mm, scabrous to glabrescent. Peduncles 5–35 mm. Involucres campanulate, 3–5 × 5–7 mm. Phyllaries suborbiculate to oblong, becoming scarious proximally, appressed-hairy distally, apices obtuse, ciliate. Paleae uniformly yellow, apices obtuse, erose. Ray florets 4–7; corollas usually white, sometimes pale yellow, laminae oblong to suborbiculate, 7–10 mm. Disc florets 8–13; corollas yellow or tinged with purple (drying reddish), 3–6 mm, lobes 1 mm. Cypselae 2.4–4 mm, 3-angled (ray) or compressed (disc), ribbed, strigose or distally ciliate; pappi usually of 1–3 unequal awns, sometimes reduced to teeth. 2n = 20, 40, or 22.
Phenology: Flowering spring–fall.
Habitat: Rocky open slopes, flats, calcareous soils
Elevation: 700–1900 m
Ariz., N.Mex., Tex., Mexico (Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Sonora, Zacatecas).
Attribution of Zinnia acerosa to Utah (S. L. Welsh et al. 1993) was based on Atwood et al. 9704 (BRY), from Moab, Grand County; the specimen was indicated as “possibly cultivated” by the collector, and it is well outside the known range of the species.