English: All possible crosses between pool frog (Pelophylax lessonae), marsh frog (P. ridibundus) and their hybrid - edible frog (P. kl. esculentus). First one is the primary hybridization generating hybrid. Second one is an example of hybridogenesis and occurs in most widespread hybridogenetic L–E system, third one occurs in R–E system (as less frequent mode among two ones) and is considered as possible i.e. in L-E system invaded by P. ridibundus too. P. kl. esculentus × P. kl. esculentus crossings result in inviable P. ridibundus tadpoles and are not shown here. Large circles - adult frogs, small circles - gametes., × - lack of gametes containing genome of one of parental species.