Plants 10-60(-120+) cm. Stems ± procumbent. Leaf blades deltate to ± rhombic or ovate, 13-37 × 7-32 mm, faces sparsely scabrellous to glabrate or glabrescent, gland-dotted. Fruits plumply ellipsoid to fusiform, weakly compressed, 7-9+ mm, 5-7-ribbed, lacking terminal spines, prickles ± uncinate, mostly along ribs. 2n = 22. Flowering year round, mostly Jul-Aug. Disturbed, often sandy sites; 0-300 m; introduced; Ala., Ark., D.C., Fla., Ga., La., Mass., Miss., N.C., Oreg., Pa., S.C., Tex., Va.; South America; also introduced in Mexico, West Indies, Central America, Europe, Asia, Africa, Pacific Islands (Hawaii). Reports of Acanthospermum xanthioides (Kunth) de Candolle from New York are evidently based on specimens of A. australe.
Stems prostrate and often rooting, to 6 dm or more, short-hairy, especially distally; lvs broadly rhombic-ovate or triangular, irregularly toothed above the cuneate, entire base, 1.5-3.5 נ1-3 cm, glandular-punctate, on petioles 3-15 mm; heads 4-6 mm wide at anthesis; burs 7-9 mm, ellipsoid-fusiform to nearly oblong, slightly compressed, densely glandular, 5-7-ribbed, the ribs bearing 1 or 2 rows of hooked prickles 1-2 mm, the top abruptly invaginated and with an evident rim; 2n=22. A weed in sandy soil and waste places, native to trop. Amer., and intr. n. occasionally as far as Mass. and Oreg.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.