Shrubs, 10-40(-60+) cm. Stems erect. Leaves mostly alternate; petioles 2-8(-12+) mm; blades (white) ovate to elliptic, 10-25(-45) × 8-15(-30) mm, (1-)2-3-pinnately lobed, abaxial and adaxial faces densely strigillose. Pistillate heads intermixed with staminates (sometimes wanting or staminates sometimes wanting, plants unisexual); florets (1-)2. Staminate heads: peduncles 0-1(-2) mm; involucres shallowly cup-shaped, 3-5 mm diam., ± strigillose; florets 8-15+. Burs: bodies ± globose, 3-5+ mm, pilosulous and/or gland-dotted, spines 12-25+, scattered, ± subulate (± navicular at bases), 2-4 mm, tips straight. 2n = 36, 72, 108, 126.
Flowering Mar-May(-Dec). Rocky or sandy washes, benches; (-100-)100-1200(-1500) m; Ariz., Calif., Nev., Utah; Mexico (Baja California, Sonora).
Common Name: burrobush
Duration: Perennial
Nativity: Native
Lifeform: Subshrub
General: Much branched, rounded shrub 10-40 cm tall; stiff branches, more or less spinose, glabrate with age, bearing short stiff hairs when young, bark gray and slightly striate.
Leaves: Alternate, on petioles 2-8 mm, blades elliptic to ovate, 2-3 pinnately lobed, both surfaces densely grayish-tomentose, 10-25 mm long by 8-15 mm wide; divisions often narrow but not linear, often variously shaped.
Flowers: On racemose or spikelike inflorescence, staminate and pistillate heads intermingled, staminate heads on peduncles 0.5-3 mm long; involucres broadly saucer-shaped, 4-5 mm wide, strigillose-cancescent, lobes 5-8, broadly triangular ovate; corollas puberulent, yellow.
Fruits: Burs 4-5.5 mm long, subglobose, moderately glandular-puberulent, 2 beaks, straight 1-1.5 mm long; spines 30-40, narrowly subulate, flattened toward base, 1.5-2.2 mm long, tips not hooked.
Ecology: Found on dry, fine soils of alluvial plains and slopes below 3,000 ft (914 m); flowers February-December.
Distribution: s UT; south to se CA and nw MEX
Notes: One of the more abundant shrubs in the desert scrub. Flattened spines on the burs are a contrast to other species of Ambrosia. Found in much of the Sonoran and Mojavean deserts, scarce only where cool-season rainfall is low, and since warm-season rain is infrequent in its range it germinates episodically.
Ethnobotany: Unknown, but other species in the genus have many uses.
Etymology: Ambrosia is Greek for food of the gods, while dumosa means bushy or shrubby.
Synonyms: Franseria dumosa
Editor: SBuckley, 2010
