Spiny cocklebur, clotbur, lampourde épineuse

Xanthium ambrosioides Hooker & Arnott; X. spinosum var. inerme Bel

Plants 10–60(–120+) cm; nodal spines usually in pairs, simple or 2–3-partite, 15–30+ mm. Leaves: petioles 1–15(–25+) mm; blades ± ovate to lanceolate or lance-linear, 4–8(–12+) × 1–3(–5+) cm, often pinnately 3(–7+)-lobed, abaxial faces gray to white, densely strigose. Burs 10–12(–15+) mm. 2n = 36.

Flowering Jul–Oct. Damp or seasonally wet, alkaline soils, waste places, margins of agriculture; 10–1000 m; N.B., Ont., Que., Sask.; Ala., Ariz., Calif., Colo., Conn., Del., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Oreg., Pa., R.I., S.C., Tenn., Tex., Utah, Va., Wash., W.Va.; Mexico; Central America; South America; widely established in Old World.

Some authors have contended that Xanthium spinosum originated in South America and is introduced and/or naturalized everywhere else that it is found.