Herbs, annual or perennial, monoecious, to 5 dm. Stems erect or prostrate, usually densely to sparsely hairy, rarely glabrous, hairs malpighiaceous. Leaves: stipules deciduous, ovate, lanceolate to subulate, 0.5–2.3 mm, margins not glandular; petiole 1–10 mm; blade elliptic to ovate, obovate, or narrowly lanceolate, 1–10.5 × 0.2–3 cm, margins serrate, serrulate, or entire, without glands, surfaces usually densely to sparsely hairy, rarely glabrous, hairs malpighiaceous. Inflorescences bisexual, 0.4–1.5 cm; bracts ovate to elliptic, 0.8–2 mm, margins without glands. Flowers without pink dye when wetted. Staminate flowers: sepals lanceolate, 0.9–2.5 × 0.4–1.4 mm; petals elliptic to obovate, 1.5–3.5 × 0.6–2 mm, free from androphore; nectary glands elliptic to oblate, 0.3–0.5 × 0.1–0.2 mm, free from androphore, glabrous; stamens 10, staminodes 0 or 3–5, glabrous. Pistillate flowers: sepals lanceolate to elliptic, 2.3–6.5 × 0.6–1.6 mm, without glands; petals 5, elliptic, 0.7–3 × 0.4–1.6 mm; nectary glands elliptic, 0.4–0.6 × 0.3–0.4 mm, glabrous; ovary sericeous, strigose, or hispidulous; styles 1–1.8 mm, glabrous; stigmas terete. Capsules 1.8–4.5 mm, strigose-hispidulous. Seeds 1.5–2.4 mm, smooth, punctate, striate, or reticulate. 2n = 26 (Baja California Sur, Mexico).
Phenology: Flowering year-round.
Habitat: Desert scrub, sandy, rocky, calcareous soils.
Elevation: 0–1600 m.
Ariz., Calif., Nev., N.Mex., Tex., Mexico, Central America (Guatemala, Nicaragua).
Argythamnia serrata is widely distributed and variable; six species have been described to recognize this variation. However, these groups overlap morphologically and geographically, and many specimens cannot be determined with confidence. A broadly defined A. serrata is therefore recognized here.