A genus of four species (twenty in one interpretation), natives of the colder parts of the northern hemisphere. They are evergreen, creeping shrubs, whose closest allies (Fallugia, Cowania and Chamaebatia) are all warmth-loving shrubs of western N. America and Mexico. The most recent treatment is: E. Hulten, ‘Studies in the Genus Dryas’, Svensk. Bot. Tidsk., Vol. 53, pp. 507–542 (1959).