Cocklebur, lampourde glouteron

Xanthium americanum Walter; X. chasei Fernald; X. chinense Miller; X. curvescens Millspaugh & Sherff; X. cylindricum Millspaugh & Fernald; X. echinatum Murray; X. echinellum Greene ex Rydberg; X. globosum C. Schull; X. inflexum Mackenzie & Bush; X. italicum Moretti; X. orientale Linnaeus; X. oviforme Wallroth; X. pensylvanicum Wallroth; X. speciosum Kearney, X. strumarium var. canadense (Miller) Torrey & A. Gray, X. strumarium var. glabratum (de Candolle) Cronquist; X. varians Greene; X. wootonii Cockerell

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.