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.

Wiggins 1964, FNA 2003

Common Name: ambrosia leaf bur ragweed Duration: Perennial Nativity: Native Lifeform: Subshrub General: Perennial subshrub with erect stems to 5 m tall with strongly striate, puberulent to tomentulose branches, which age glabrate. Leaves: Alternate on petioles 2-3 cm long, tomentulose, often scurfy, the blades ovate to lance-ovate in outline, 5-8 cm wide and 8-22 cm long, margins coarsely toothed, strongly veined below, darker green and puberulent to scaberulous above, the lobes and apex usually acute to acuminate. Flowers: Heads conspicuously paniculate, with rotate involucres 5-6 mm across, deeply cleft into 6-12 lanceolate lobes, the palea puberulent, shorter than tubular corollas, the latter 1.5 mm long, the pistillate heads with 2-3 flowers, subtended by linear bracts 3-6 mm long. Fruits: Burs that are elliptic, hirsutulous, 8-9 mm high, bearing 2 elongate but slightly hooked beaks, 7-12 spines in 3 series. Ecology: Found along washes and in canyons from 500-4,000 ft (152-1219 m), flowers March-May. Distribution: Ranges across the Sonoran Desert and south to Durango, along with south into Baja California and into Chihuahua. Notes: Distinctive smell helps to distinguish this plant in season with its sweet odor, along with the large toothed and very green leaves. Ethnobotany: Used as an analgesic for menstrual pains and used as a poultice applied to the chest to loosen a cough. Etymology: Ambrosia is Greek for food of the gods, while ambrosioides means like ambrosia. Synonyms: Fransia ambrosioides, Xanthidium ambrosioides Editor: SBuckley 2011