24. Euphorbia albomarginata Torrey & A. Gray in War Department [U.S.], Pacif. Railr. Rep. 2(4): 174. 1857.
Rattlesnake weed, white-margin sandmat or sandwort Rattlesnake weed, white-margin sandmat or sandwort
Chamaesyce albomarginata (Torrey & A. Gray) Small
Herbs, perennial, with moderately to strongly thickened rootstock. Stems prostrate, occasionally mat-forming, frequently rooting at nodes, 10–80 cm, glabrous. Leaves opposite; stipules connate into conspicuous, deltate or ovate scale, white, 0.4–1(–2) mm, glabrous; petiole less than 1 mm, glabrous; blade ovate, oblong or orbiculate, 3–8(–15) × 3–7 mm, base strongly asymmetric, obtuse to hemicordate, margins whitish, entire, apex obtuse, rarely mucronulate, surfaces often with red blotch in center, glabrous; 3-veined from base but usually only midvein conspicuous. Cyathia solitary at distal nodes; peduncle 1–4 mm. Involucre campanulate, 0.8–1.1 × 0.9–2 mm, glabrous; glands 4, greenish yellow to red, usually oblong to reniform, rarely subcircular, 0.2–0.5 × (0.2–)0.3–0.8 mm; appendages white to pink, flabellate to oblong, 0.3–1 × 0.6–1.3 mm, distal margin entire or crenulate to erose. Staminate flowers 15–30. Pistillate flowers: ovary glabrous; styles 0.3–0.7 mm, 2-fid nearly entire length. Capsules broadly ovoid, 1.1–2.3 × 1.2–2 mm, glabrous; columella 1.1–1.6 mm. Seeds white to gray or brownish red, oblong-ovoid, 4-angled in cross section, 1–1.7 × 0.5–0.8 mm, smooth.
Flowering and fruiting year-round. Disturbed areas in desert scrub, grasslands, mesquite woodlands, chaparral; 0–2300 m; Ariz., Calif., Colo., Nev., N.Mex., Okla., Tex., Utah; Mexico; introduced in Pacific Islands (Hawaii).
Euphorbia albomarginata is native to northern and central Mexico and the southwestern and south-central United States. The species occurs in a variety of habitats in western North America and in some areas is quite weedy. It has been recorded as a waif in Louisiana.