Plants of the genus Arctium have dark green leaves that can grow up to 70 cm (28 in) long. They are generally large, coarse and ovate, with the lower ones being heart-shaped. They are woolly underneath. The leafstalks are generally hollow. Arctium species generally flower from July through to October. Burdock flowers provide essential pollen and nectar for honeybees around August when clover is on the wane and before the goldenrod starts to bloom
The prickly heads of these plants (burrs) are noted for easily catching on to fur and clothing. In England, some birdwatchers have reported that birds have become entangled in the burrs leading to a slow death, as they are unable to free themselves. Burdock's clinging properties, in addition to thus providing an excellent mechanism for seed dispersal, led to the invention of Velcro.
A large number of species have been placed in genus Arctium at one time or another, but most of them are now classified in the related genus Cousinia. The precise limits between Arctium and Cousinia are hard to define; there is an exact correlation between their molecular phylogeny. The burdocks are sometimes confused with the cockleburs (genus Xanthium) andrhubarb (genus Rheum).