Ambrosia chamissonis

Perennials, 50-150(-350+) cm. Stems prostrate or decumbent. Leaves mostly alternate; petioles 15-30(-45+) mm; blades rounded-deltate to ovate or obovate, 20-45(-70+) × 10-25(-50+) mm overall, not lobed or 1-2(-3)-pinnately lobed, bases cuneate, ultimate margins entire or toothed, abaxial and adaxial faces strigillose to sericeous. Pistillate heads clustered, proximal to staminates; florets 1. Staminate heads: peduncles 0.5-2 mm; involucres shallowly cup-shaped, 4-6+ mm diam., strigillose; florets 8-25(-50). Burs: bodies fusiform to ± pyriform, 4-7+ mm, ± strigillose to pilosulous, spines 8-16+, scattered, stoutly conic or flattened- to triquetrous-subulate, 0.5-1.5+ mm, tips straight. 2n = 36.

Flowering Apr-Nov. Sandy beaches and strand; 0-10 m; B.C.; Alaska, Calif., Oreg., Wash.; Mexico (Baja California).