SouthW. Naturalist 5: 170. 1960.
Herbs, annual or short-lived perennial, with usually slender, occasionally slightly thickened, rootstock. Stems prostrate to reclining, 5–40 cm, glabrous. Leaves opposite; stipules distinct, subulate, 0.5–0.7 mm, glabrous; petiole 0.7–1.3 mm, glabrous; blade orbiculate, oval, to shortly oblong, 1–3.2 × 1.5–5 mm, base subsymmetric, rounded, margins entire, apex usually rounded, occasionally emarginate, surfaces glabrous; venation obscure, only midvein conspicuous. Cyathia solitary at distal nodes; peduncle 0.3–0.7 mm. Involucre turbinate to campanulate, 0.8–1.2 × 0.7–1 mm, glabrous; glands 4, red to purple, slightly concave, elliptic, 0.2–0.3 × 0.4–0.5 mm; appendages absent. Staminate flowers 15–36. Pistillate flowers: ovary glabrous; styles 0.2–0.3 mm, 2-fid nearly entire length. Capsules broadly ovoid, 1.3–1.8 × 1.5–2 mm, glabrous; columella 1.1–1.4 mm. Seeds whitish, reddish brown beneath coat, oblong, 4-angled in cross section, 1.5–2 × 1.3–1.8 mm, with 5–7 faint transverse ridges or wrinkles. 2n = 28.
Phenology: Flowering and fruiting year-round.
Habitat: Desert scrub, mountains, hills, canyons, arroyos, flats, roadsides, clay, sandy, gravelly, and rocky soils.
Elevation: 600–1300 m.
Tex., Mexico (Chihuahua, Coahuila).
Euphorbia simulans, which in the flora area is known only from Brewster, Hudspeth, and Presidio counties, is difficult to distinguish in the field from the sympatric E. theriaca var. theriaca, because they are mainly distinguished by seed morphology. The latter has smaller seeds with (two or) three (or four) prominent transverse ridges, whereas E. simulans has larger seeds that are slightly wrinkled.