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.

Plant: Shrub < 2.5 m, generally dark; stems coarsely long-hairy or bristly Leaves: opposite below, generally alternate above, generally petioled, hairy, glandular; blade 2-20 cm, ± lanceolate, coarsely toothed, dark green, sticky, fragrant INFLORESCENCE: staminate heads generally many in ± spikes or racemes, 6-8 mm diam; involucre lobes 7-12; pistillate heads 3-5-flowered, generally clustered below staminate, generally spiny, bur-like; receptacle chaffy; chaff scales spirally arrayed, fused below, tips generally becoming spiny Flowers: Staminate flowers ± many; corolla yellow or translucent; anthers free; style unbranched; Pistillate flowers 1-5; corolla 0; style branches long Fruit: Fruit: enclosed in bur 10-15 mm, elliptic, ± brown, finely glandular; spines generally > 50, scattered, ± cylindric, hooked; pappus 0 Misc: scrub; < 100 m. Notes: receptacle envelopes pistils in spiny covering References: J.C. Hickman, ed. The Jepson Manual.L. Benson & R. Darrow. Trees and Shrubs of the Southwestern Deserts. Kearney & Peebles. Arizona Flora. ASU specimens.