Ambrosia chenopodiifolia

Shrubs, 30-80+ cm. Stems erect. Leaves mostly alternate; petioles 5-20 mm; blades ovate to rounded-deltate, 20-35(-50) × 18-30(-45) mm, bases broadly cuneate to ± truncate, margins toothed, abaxial faces ± densely tomentulose (between veins), adaxial faces sparsely tomentulose, glabrescent. Pistillate heads clustered, proximal to staminates; florets 2(-3). Staminate heads: peduncles 0-3 mm; involucres ± cup-shaped, 3-5 mm diam., tomentulose; florets 12-20+. Burs: bodies obconic to fusiform, 4-6 mm, tomentulose (little, if at all, stipitate-glandular), spines 15-20+, scattered or on distal ¹/2, ± subulate (the proximal basally flattened), 2-3 mm, tips usually uncinate, sometimes straight. 2n = 72.

Flowering Mar-Apr. Clays or sandy soils, among lava rocks; 50-200 m; Calif.; Mexico (Baja California, Baja California Sur).