What is the X in X-mas?
group of North American frogs (family Ranidae) occurring throughout North America (except in the coastal band from California to British Columbia) from northern Canada southward into Mexico. At one time the leopard frog was considered a single species, Rana pipiens, but during its wide use as a laboratory frog from the 1940s to the 1960s, developmental and physiological differences were noted in frogs from different geographic areas. These differences and the distinct morphologies indicated that several species were characterized by a similar colour pattern. At present, leopard frogs are contained within the Pantherana clade, which is known informally as the Rana pipiens complex. In the United States and Canada, nine species are recognized: R. berlandieri, the Rio Grande leopard frog; R. blairi, the Plains leopard frog; R. chiricahuensis, the Chiricahua leopard frog; R. fisheri, the Vegas Valley leopard frog (now extinct); R. onca, the relict leopard frog; R. pipiens, the northern leopard frog; R. sphenocephala, the southern leopard frog; R. subaquavocalis, the Ramsey Canyon leopard frog; and R. yavapaiensis, the lowland leopard frog. All leopard frogs are relatively slender-bodied and long-legged, with pointed snouts. They range from about 6 to 10 cm (2 to 4 inches) in head-body length. All have a pattern of ellipsoidal to circular dark spots on their backs; the size, shape, and colour of these spots differ between species. All are semiaquatic frogs and generally associated with marshy habitats.