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This hybrid form displays a morphology intermediate between its parental species, the Pool Frog (Rana lessonae) and the Marsh Frog (R. ridibunda). This trait is revealed, in particular, in the values of some characters having identification value. When the shins are positioned perpendicularly to the body axis, the heels contact. Inner metatarsal tubercle 1.73-2.89 times shorter than the first toe. Dorsal coloration greyish-green, olive-green or green with dark spots which vary in size and number. Light middorsal line from snout to cloaca usually present. No temporal spot. Belly light, usually with dark spots. Male vocal sacs positioned behind the mouth angles and are grey.
Rana esculenta is the hybrid of R. ridibundaand R. lessonae. Together with diploid individuals, hybrid populations may also contain triploids. Great variability in the population systems of these three forms exists within the range, where the hybrid (or either parental) form may coexist or not coexist with the both (or any) other forms. Genetic, ecological and behavioral studies in these frogs are in progress.