J. Arnold Arbor. 45: 410. 1964
Shrubs, 60–150+ cm. Stems erect. Leaves mostly alternate; petioles 10–35 mm; blades lanceolate to narrowly triangular, 50–150+ × 18–55+ mm, bases truncate to cordate, margins coarsely toothed (not spiny), abaxial and adaxial faces ± hirsutulous and gland-dotted. Pistillate heads clustered on lateral axes, proximal to staminates; florets 4–5. Staminate heads: peduncles 2–4(–12) mm; involucres ± saucer-shaped, 4–6+ mm diam., ± hirsutulous; florets 40–60+. Burs: bodies ± fusiform, 6–8+ mm, stipitate-glandular, spines 60–80+, scattered, subulate, 4–6 mm, tips uncinate. 2n = 36.
Phenology: Flowering Mar–May.
Habitat: Sandy soils, washes, banks
Elevation: (100–)500–1000+ m
Ariz., Calif., Mexico (Baja California, Baja California Sur, Chihuahua, Durango, Sonora).
Ambrosia ambrosioides has been reported from California; it may occur there.