Stems densely bristly with spreading or slightly descending prickles 4–8 mm and mostly less than 0.5 mm diam. at base, 25+ per cm of stem, sparsely pubescent with short-stipitate glands. Calyx lobes 3.3–3.5 mm. Seeds with low, radially oriented ridges.

Flowering Jul–Oct. Limestone, lava, sand, alluvial deposits, calcareous, gypseous, and saline flats, around wet depressions; 1100–1400 m; Tex.; Mexico (Chihuahua, Coahuila).

Variety setigerum is found occasionally in Presidio County, where it is becoming a serious nuisance in overgrazed and irrigated lands.