Ambrosia grayi

Perennials, 10-30+ cm. Stems erect. Leaves mostly alternate; petioles 10-45+ mm; blades elliptic to ovate, 45-60(-100+) × 30-45(-75+) mm, usually 1-2-pinnately lobed (lobes ± lanceolate), bases cuneate, ultimate margins serrate, abaxial faces densely sericeous or strigillose (silver or grayish), adaxial faces strigillose. Pistillate heads clustered, proximal to staminates; florets (1-)2. Staminate heads: peduncles 1-2 mm; involucres saucer-shaped, 3.5-5+ mm diam., strigillose; florets 8-25(-40+). Burs: bodies ± pyriform to globose, 3-5+ mm, stipitate-glandular, spines 8-12+, scattered, stoutly conic, 0.5-1+ mm, tips straight. 2n = 36.

Flowering Aug-Sep. Wet or seasonally wet flats, depressions, alkaline, clay soils, prairies; 600-1200 m; Colo., Kans., Nebr., Okla., Tex.