Stems with spreading prickles 3–7 mm and often to 1 mm diam. at base, fewer than 20 per cm of stem, densely pubescent with short-stipitate glands and often with unbranched, spread­ing hairs to 1 mm. Calyx lobes 2.5–3.8 mm. Seeds reticulately wrinkled or merely undulate.

Flowering Apr–Oct. Well-drained, often igneous, rocky or sandy soils, sparsely vegetated mountainsides, dry grasslands, disturbed places; (100–)1300–1900 m; Fla., Tex.; Mexico (Coahuila).

Variety citrullifolium is found in central and western Texas south to Mexico. The plants from central Texas differ from those of western Texas and Mexico in having more rounded ultimate leaf lobes, leaf undersides often lacking stellate hairs, and longer fruiting inflorescences. In Florida, var. citrullifolium has escaped from cultiva­tion and become naturalized. Massachusetts records (F. C. Seymour 1982) are historical (1885, 1913, 1949) as introductions that did not persist.