Cocklebur arrived in the U. S. uninvited. It was a stowaway with the first shipment of goats and sheep brought to America by early settlers. The weed has spread from coast to coast. It is the common species in the north central sections of the country. It has spread along the East and West coasts and the Gulf area.
Cockleburs are members of the Compositae.
Sterile and fertile flowers appear on various heads of the same plant. The seeds enclosed within the spiny burs are two-celled, with one ovule in each cell. The ovules germinate in consecutive seasons - a design that makes the weed difficult to control. Cockleburs became a national problem in South Africa when European settlers established their great sheep ranches. The burs diminished the quality of the wool and seedling plants poisoned the livestock that ate them.