9. Ambrosia deltoidea (Torrey) W. W. Payne, J. Arnold Arbor. 45: 421. 1964.
Franseria deltoidea Torrey, Smithsonian Contr. Knowl. 6(2): 15. 1853
Shrubs, 30–80+ cm. Stems erect. Leaves mostly alternate; petioles 5–12+ mm; blades deltate to lance-deltate, 12–25(–35) × 5–12(–18) mm, bases 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 0.5–3(–5) mm; involucres ± cup-shaped, 4–8 mm diam., tomentulose; florets 12–30+. Burs: bodies ± fusiform to globose, 3–4 mm, usually stipitate-glandular (little, if at all, tomentulose), spines 20–30+, scattered or on distal 1/2, ± subulate (the proximal basally flattened), 1–3 mm, tips usually straight, sometimes uncinate. 2n = 36.
Flowering Feb–May. Sandy washes, benches; 200–1000 m; Ariz.; Mexico (Baja California, Sonora).
Some specimens are intermediate for the char-acteristics that distinguish Ambrosia deltoidea and A. chenopodiifolia. The type of A. deltoidea may be better treated as conspecific with that of A. chenopodiifolia.