Monographs Details: Xanthium strumarium L.
Authority: Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Description:Species Description - Plants 2–20 dm, appressed-hairy or subglabrous; lvs long-petiolate, broadly ovate to suborbicular or reniform, generally cordate or subcordate at base, sometimes shallowly 3–5-lobed, often 15 cm; staminate heads in a terminal cluster, the pistillate ones in several or many short axillary infls; bur broadly cylindric to ovoid or subglobose, 1–3.5 cm, covered with stout hooked prickles, terminated by 2 straight or in ours ± incurved beaks; 2n=36. Fields, waste places, flood-plains, and lake- and sea-beaches; now a cosmopolitan weed, probably originally native only to the New World. July–Sept. Our most common phase is var. canadense (Mill.) Torr. & A. Gray, with the burs brownish or yellowish-brownish, 2–3.5 cm, the lower part of the prickles conspicuously spreading-hairy as well as ± stipitate-glandular. (X. echinatum; X. italicum; X. pensylvanicum; X. speciosum) Also found throughout our range is var. glabratum (DC.) Cronquist, with merely atomiferous- glandular or glandular-puberulent to subglabrous, commonly paler burs seldom over ca 2 cm. (X. americanum; X. chinense; X. cylindraceum; X. echinellum; X. globosum; X. inflexum) Var. strumarium, with straight-beaked, yellow-green, merely puberulent burs to 2 cm, occurs in tropical Amer. and in s. Europe, and rarely in our range as a waif.
Common Names:common cocklebur