Euphorbia theriaca

L. C. Wheeler

Rhodora 43: 242, plate 660, fig. A. 1941.

Common names: Terlingua sandmat
Synonyms: Chamaesyce theriaca (L. C. Wheeler) Shinners
Treatment appears in FNA Volume 12. Treatment on page 290. Mentioned on page 258, 270, 282.

Herbs, annual, with slender taproot. Stems prostrate to reclining, not mat-forming, 5–30 cm, glabrous. Leaves opposite; stipules usually distinct, occasionally connate basally on lower side of stem, subulate or scalelike, usually entire, occasionally 2-fid or margin sparsely ciliate, 0.4–1 mm, glabrous; petiole 0.7–1.2(–1.5) mm, glabrous; blade ovate, oblong, orbiculate, or obovate, 2–7.1 × 1–3.5 mm, base slightly asymmetric, rounded, margins entire, often revolute on drying, apex usually rounded, occasionally slightly emarginate, surfaces glabrous; venation usually obscure, only midvein conspicuous. Cyathia usually solitary at distal nodes, rarely clustered on short, axillary branches; peduncle 0.3–1.3 mm. Involucre usually turbinate-campanulate to hemispheric, occasionally suburceolate, 1–1.8 × 0.9–1.4 mm, glabrous; glands 4, yellow-green to red-purple, sessile or short-stipitate, subcircular to slightly elliptic, 0.2–0.5 × 0.2–0.7 mm; appendages absent or white to pink, semilunate or forming rim at edge of gland, (0–)0.1–0.4 × (0–)0.3–0.9 mm, entire or slightly crenate. Staminate flowers 15–36. Pistillate flowers: ovary glabrous; styles 0.3–0.5 mm, 2-fid 1/2 length. Capsules broadly ovoid, 1.1–1.6 × 1.5–1.8 mm, glabrous; columella 1.2–1.5 mm. Seeds whitish, reddish brown beneath coat, ovate, 4-angled in cross section, 0.8–1.2 × 0.5–0.8 mm, with (2–)3(–5) deep transverse ridges. 2n = 28.


Varieties 2 (2 in the flora).

Selected References



1 Involucral glands sessile, appendages absent. Euphorbia theriaca var. theriaca
1 Involucral glands short-stipitate, appendages present, occasionally rudimentary. Euphorbia theriaca var. spurca