SouthW. Naturalist 5: 170. 1960.
Herbs, perennial, with strongly thickened, woody rootstock. Stems erect, 7–45 cm, glabrous. Leaves opposite; stipules distinct, linear-filiform in (1–)2(–3) segments, 0.3–0.4 mm, glabrous; petiole 0.8–2 mm, glabrous; blade ovate or orbiculate-deltate to reniform-deltate, 5–17 × 4–16 mm midstem leaves largest, base symmetric, cuneate, rounded to cordate, margins entire, apex acute to rounded, surfaces glabrous, often glaucous; 3-veined from base, only midvein conspicuous. Cyathia solitary at distal nodes or at nodes of short, axillary branches; peduncle 1.8–3 mm. Involucre broadly-campanulate to hemispheric, 1.7–2.2 × 1.5–2.7 mm, glabrous; glands 4, green to yellow-green, elliptic to oblong, folded longitudinally, 0.3–0.5 × 0.7–1.4 mm; appendages absent. Staminate flowers 35–45. Pistillate flowers: ovary glabrous; styles 0.7–0.9 mm, 2-fid nearly entire length. Capsules subglobose to broadly ovoid, 2.8–3.3 × 2.8–3.4 mm, glabrous; columella 2.2–2.7 mm. Seeds white to light brown, ovoid, 3–4-angled in cross section, 2–2.4 × 1–1.2 mm, smooth to faintly transverse-wrinkled.
Phenology: Flowering and fruiting spring–fall.
Habitat: Desert scrub, on cretaceous and gypseous clay, limestone hills and flats.
Elevation: 900–1200 m.
Tex., Mexico (Chihuahua).
Euphorbia perennans is a distinctive species with an erect habit and relatively large, firm, deltate midstem leaves. Phylogenetic data place E. perennans in a clade of primarily Chihuahuan Desert annual and perennial species (for example, E. chaetocalyx, E. fendleri, E. golondrina, E. simulans, E. spurca, and E. theriaca; Y. Yang and P. E. Berry 2011).
Euphorbia perennans is known in the flora area only from Brewster County.