Shrubs, 30-50+ cm. Stems erect. Leaves mostly alternate; petioles 3-35 mm; blades deltate to rounded-deltate, 10-35(-80) × 10-30(-70) mm, bases cordate to truncate, margins coarsely toothed, abaxial faces densely puberulent (including veins), adaxial faces strigillose to scabrellous and gland-dotted. Pistillate heads clustered, proximal to staminates; florets (1-)2. Staminate heads: peduncles 0-1 mm; involucres cup-shaped, 2-3(-5) mm diam., strigillose; florets 8-30+. Burs: bodies ± globose to fusiform, 3-4+ mm, tomentulose and stipitate-glandular, spines 8-20+, scattered, ± subulate (basally navicular), 1-2 mm, tips straight or uncinate.

Flowering Mar-Apr. Sandy washes, benches; 700-1200 m; Ariz.; Mexico (Sinaloa, Sonora).

Common Name: Tucson burr ragweed

Duration: Perennial

Nativity: Native

Lifeform: Subshrub

General: Shrubby perennial, 30-50+ cm tall, with several slender ascending branches from a woody base; branches minutely but densely white-tomentose when young, growing to sparingly floccose or glabrate, striate, silvery.

Leaves: Mostly alternate, on slender petioles, those nearly or quite equaling blades in length; blades ovate-cordate in outline, 1-5 cm broad, 2-7 cm long, moderately 3-7 lobed and coarsely dentate, densely cinereous-tomentulose on lower surface, deep green and often scaberulous on upper surface.

Flowers: Pistillate and staminate flowers in separate heads; all heads discoid; staminate heads arranged in terminal racemes to 15 cm long; pistillate heads solitary or in small clusters at base of raceme. Staminate involucres saucer-shaped, 2-5 mm in diameter, densely puberulent in youth, later subglabrate, with 8-30 florets, the corollas finely puberulent, brownish. Pistillate heads 2-flowered, maturing to a single bur.

Fruits: Bur ellipsoidal, 5-7 mm long, densely glandular-puberulent, with 8-20 hooked spines.

Ecology: Found in canyons, arroyos, and on rocky slopes from 1,500-3,500 ft (457-1067 m); flowers January-April.

Distribution: s AZ, south to Sonora and Sinaloa, MEX.

Notes: Ambrosias are shrubs or herbs with unisexual flowering heads heads of all disk flowers, the female heads maturing into hard fruits or spiny burs. This low shrub is distinguished from other Ambrosia spp. by its leaves, which are heart-shaped, bluntly toothed and lobed, with silvery veins.

Ethnobotany: Unknown for this species, but many other uses for species in this genus.

Etymology: Ambrosia is Greek for food of the gods, while cordifolia means heart-shaped leaves.

Synonyms: Franseria cordifolia

Editor: SBuckley 2010, AHazelton 2015