Virginia Tech Weed Identification Guide

Common Cocklebur: Xanthium strumarium

Weed Description: A summer annual that produces a conspicuous prickly 'cocklebur' and ranges from 1/2 to 6 1/2 feet in height.  Common cocklebur is found throughout the United States and is primarily a weed of agronomic and horticultural crops, nurseries, and occasionally pastures.

Seedlings:  The stem below the cotyledons (hypocotyl) is purple at the base and often green in the upper portion.  Cotyledons are linear to oblong in outline, waxy, smooth, fleshy, thick, approximately 3/4 to1 3/4 inches long and usually no more than 1/2 inch wide.  The first true leaves are opposite, while all subsequent leaves are alternate.

Leaves:  The first true leaves are opposite, all subsequent leaves are alternate.  Leaves are triangular to ovate in outline, have stiff hairs, and are approximately 2 to 6 inches long.   Leave are irregularly lobed with leaf margins that have relatively inconspicuous teeth.  Leaves occur on long petioles and also have three prominent veins on the upper surface of the leaf that arise from the same point.  cocklebur9-24.jpg (108975 bytes)
Stems:  Erect, branched, stout and covered with a dense cover of short stiff ascending hairs and 'bumps'. Stems are ridged longitudinally and green with maroon to black spots.  Stems may reach 6 1/2 feet in height.

Roots: A taproot.

Flowers:   Inconspicuous, greenish in color, arising from the area between the leaf petioles and the stems (axillary flowers) and at the ends of the erect stems (terminal flowers).

Fruit:  An elliptic to egg-shaped two-chambered bur, 1/2 to 1 1/2 inches long and covered with hooked prickles. Each bur contains two seeds, one that grows during the first year and one that grows a year later.  Two prickles that are longer and wider than the remaining prickles project from the tip of the bur.

Identifying Characteristics:   The relatively large, linear to oblong waxy cotyledons helps to distinguish this weed in the early stages of development.  Additionally, the long-petiolated triangular leaves, stems with maroon to black stem lesions, and the distinctive prickly cocklebur fruit are all features that help in the identification of this weed.  In the early stages of development, this weed might be confused with Giant Ragweed (Ambrosia trifida), however the cotyledons of common cocklebur are much longer and more linear than those of giant ragweed.  Spiny Cocklebur (Xanthium spinosum) is a closely related and similar species, however, unlike common cocklebur, this weed has very distinctive 3-parted spines that arise at the base of each leaf.