Plants 10-80(-200) cm; nodal spines 0. Leaves: petioles 20-100(-140+) mm; blades suborbiculate to ± pentagonal or deltate, 4-12(-18+) × 3-10(-18+) cm, sometimes palmately 3-5-lobed, abaxial faces green, hirtellous. Burs 10-30+ mm. 2n = 36. Flowering Jul-Oct. Damp or seasonally wet, often alkaline, soils, waste places, margins of agriculture; 10-2000 m; Alta., B.C., Man., N.B., N.S., Ont., P.E.I., Que., Sask.; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; Central America; South America; widely introduced in Old World. Recognition of a dozen or more taxa (treated as species, subspecies, varieties, and/or forms) has been proposed for plants treated together here as Xanthium strumarium. Bases for the various taxa mostly involved subtle differences in the burs.

Plant: Monoecious annual forb to 80 cm; herbage glandular and scabrous Leaves: leaves alternate, long-petiolate, blades 5-15 cm wide and long, often 3-lobed, margins serrate INFLORESCENCE: primary inflorescence a head, each resembling a flower; staminate heads in clusters, involucre 0, receptacle chaffy; pistillate heads clustered below staminate heads, 2-flowered, 2-beaked, spiny, bur-like; phyllaries 0 or minute; chaff scales many, spirally arrayed, fused below, free tips spiny, hooked Flowers: Staminate flowers many; corolla translucent; filaments fused, attached to corolla tube base, anthers free; ovary slender; Pistillate flowers generally 2 per head; corolla 0; style branches long Fruit: Fruit: 2, enclosed in bur, germinating in successive years; bur cylindric to barrel-shaped; spines generally stout, ± glandular; pappus 0 Misc: Disturbed areas; generally < 500 m.; Jul-Oct Notes: Flower has no corolla or pappus.Stamens monodelphous.Style unbranched.The spines on the fruit may be glandular. References: McDougall; Seed plants of Northern Arizona. Hickman, ed.; The Jepson Manual. ASU specimans