Leaves 1–4+ cm, lobes 0.5–1(–3) mm wide. Ray laminae 1–2+ mm. Disc corollas ca. 2.5 mm. Cypselae 5–18 mm; pappi 0.5–1(–3) mm. 2n = 48, 50.

Flowering Jun–Oct. Igneous and calcareous soils; 900–2500 m; Ariz., N. Mex., Tex.; Mexico; Central America.

Heterosperma pinnatum occurs throughout much of the southwestern United States. No specimens have been seen to substantiate claims of occurrences in Maryland and Massassachusetts, where it may have been ephemeral. Calyculi of H. pinnatum have been interpreted as leaves, the heads being interpreted as terminal and sessile.