Xanthium strumarium L. is an annual weed found in all provinces of Canada except Newfoundland, and throughout the temperate and subtropical regions of the world. It occurs in ruderal habitats, waste places, agricultural fields, and along watercourses, beaches and coastal dunes. Throughout its range, populations vary widely in fruit size and morphology and in photoperiodic requirements. It has been used extensively as an experimental plant in studies of floral induction, leaf development, stomatal control, seed germination, and biological control.Key words: Cocklebur, reproductive biology, weed, Xanthium