4. Ambrosia ambrosioides (Delpino) W. W. Payne, J. Arnold Arbor. 45: 410. 1964.
Xanthidium ambrosioides Delpino, Studi Lign. Anemof. 63 (1871)
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.
Flowering Mar–May. Sandy soils, washes, banks; (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.