Shrubs, 30–150(–400) cm. Stems erect. Leaves mostly alternate; petioles 0; blades mostly filiform, 5–30(–65+) × 0.5–1.5 mm, sometimes with 3(–5+) filiform lobes, abaxial faces glabrous or glabrate, often vernicose, adaxial faces densely scabrellous (white). Pistillate heads ± intermixed with staminates; florets 1. Staminate heads: peduncles 0–0.5 mm; involucres ± cup-shaped, 2–4 mm diam., ± glabrate, ± vernicose; florets 5–12+. Burs: bodies fusiform to pyriform, 4–5 mm, stipitate-glandular, wings 7–12+, mostly around middles, oblanceolate to cuneiform, 2–3 × 1–2 mm. 2n = 36.
Phenology: Flowering (May–)Aug–Nov.
Habitat: Desert washes, ravines
Elevation: 10–500 m
Ariz., Calif., N.Mex., Tex., Mexico (Baja California, Baja California Sur, Chihuahua, Sinaloa, Sonora).
Ambrosia monogyra may occur in western Nevada.