Aquatic and Wetland Vascular Plants of the Northern Great Plains
49. Asteraceae, the Aster Family
19. Xanthium L. -- Cocklebur1. Xanthium strumarium L.
Weedy taprooted annual 2-8 dm tall, simple to much branched; stem rough due to coarse, appressed hairs, often dark brown spotted. Leaves simple, alternate, the blades broadly ovate to suborbicular or reniform, often weakly 3- to 5-lobed, 3-15 cm long, narrower to wider than long, scabrous, minutely punctate, bluntly toothed, obtuse to truncate or cordate at the base; petioles 3-10 cm long. Heads small, unisexual and dimorphic, in axillary clusters, the male florets in small heads above the larger female heads; male heads nearly spherical, many-flowered, ca. 5 mm in diameter; involucres of 1-3 series of separate bracts; receptacle cylindric, chaffy; florets minute, their corollas brownish, filaments monadelphous, the nonfunctional pistil consisting mainly of an undivided style; female heads with a spiny involucre completely enclosing 2 florets, forming a conspicuous 2-chambered bur with hooked prickles; corolla none; burs ultimately yellow-brown to brown, ellipsoid, 1.5-3 cm long, with 2 prominent, hard, often incurved beaks at the tip, the body and spines of the bur typically covered with spreading hairs and stipitate glands. Achenes thick, one in each chamber of the bur. Late Jul--Sep. Shores, stream banks, wet meadows, sand bars, often where disturbed, also fields, roadsides and waste places; common; (A cosmopolitan weed probably originating in America). X. italicum Mor.
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