Ambrosia pumila

Perennials, 10-20(-40+) cm. Stems erect. Leaves mostly alternate (sometimes crowded at bases of stems); petioles 5-35(-55) mm; blades deltate to elliptic, 15-35(-75) × 12-25(-45) mm overall, laciniately (1-)2(-3)-pinnately lobed, bases cuneate to truncate, ultimate margins entire, abaxial and adaxial faces ± strigillose to sericeous (often grayish) and gland-dotted. Pistillate heads clustered, proximal to staminates; florets 1. Staminate heads: peduncles 0.5-6 mm; involucres obliquely cup-shaped, 3-5 mm diam., ± strigillose; florets 8-25+. Burs: bodies ± fusiform, 2-2.5 mm, strigillose, spines or tubercles 0 or 1-5, mostly distal, stoutly conic, 0.1-0.5 mm, tips straight. 2n = 72.

Flowering May-Jun(-Oct). Disturbed sites, damp to wet, alkaline soils; 100-200 m; Calif.; Mexico (Baja California).