Cocklebur, or Clotbur, any of several species of annual weeds of the composite family found in many parts of the world. The plants are six to eight feet (1.8 to 2.4 m) tall, with numerous branched stems and coarse, heart-shaped leaves. The male, or pollen-bearing, flowers grow on the upper branches, while the female, or seed-producing, flowers grow on the lower branches of the same plant.

All the plants have spiny burs. The burs are hard and woody, about one inch (2.5 cm) long, and usually contain two seeds. They are troublesome to farm animals, as they cling to the hair and are hard to remove. The weeds before they go to seed are easily controlled by the use of the chemical 2,4-D.

The cocklebur is of the genus Xanthium, family Compositae.

The cockleburThe cocklebur is a weed with spiny, prickly burs.