Carduus is a genus of flowering plants in the aster family, Asteraceae, and the tribe Cynareae, one of two genera considered to be true thistles, the other being Cirsium. Plants of the genus are known commonly as plumeless thistles. They are native to Eurasia and Africa, and several are known elsewhere as introduced species. This genus is noted for its disproportionately high number of noxious weeds compared to other flowering plant genera.