HYBRIDIZATION IN THE EVOLUTION OF BATRACHIUM

Summary Three groups of species can be distinguished in Ranunculus subgenus Batrachium with respect to their leaf form. The first group of species produce only entire leaves and are primarily terrestrial. The second group produce only dissected leaves and all species are submerged aquatics. The third group is heterophyllous and the species produce both entire and divided leaves. The heterophyllous species are adapted to fluctuating water levels. The control of heterophylly is complex. When heterophyllous species are crossed the F 1 offspring are unstable in leaf form, but in the Fa stable, non‐heterophyllous segregants are found which in one jump may be preadapted to terrestrial or submerged conditions. Such decreased epigenctic versatility in hybrids may be important in the evolution of higher plants.