Porophyllum macrocephalum de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 648. 1836; P. ruderale subsp. macrocephalum (de Candolle) R. R. Johnson

Annuals, 15–50+ cm; internodes mostly 15–30+ mm. Leaf blades oval or elliptic to obovate, 15–35+ × 8–25+ mm. Phyllaries 5, linear, 15–25+ mm. Florets mostly 30–50+; corollas greenish to purplish, 9–12.5 mm. Cypselae 9–12 mm; pappi: longer bristles 7–10 mm. 2n = 22.

Flowering late summer–fall. Ephemerally wet sites in desert mountains; 1000–1500 m; Ariz., N.Mex., Tex.; Mexico; West Indies (Antilles); Central America; South America.