Hidden Diversity of Ranunculus Sect. Batrachium in the Pannonian Basin: A Mediterranean Trace in Central Europe?

Ranunculus sect. Batrachium is one of the most taxonomically challenging groups of aquatic plants. The main factors contributing to this complexity include morphological reduction, phenotypic plasticity, polyploidy and hybridization. In this study, Batrachium diversity in the Pannonian Basin was investigated for the first time using molecular methods combined with morphological evaluation, genome size measurements and chromosome counting. Across 51 sampled populations, we identified seven traditionally recognized species known from other parts of central Europe, along with several hybrids, some of which have a complex origin involving backcrossing and introgression. Remarkably, we identified four previously unrecognized non-hybrid cytotypes, two of them belonging to the Ranunculus peltatus complex and two to the Ranunculus trichophyllus complex. DNA sequences indicate that these novel cytotypes are closely related to specific Mediterranean lineages of the European Batrachium species, either as their direct descendants or through unsampled or unknown ancestors closely related to them. The Pannonian Basin hosts a more diverse array of Batrachium lineages than previously described, including elements highly similar to Mediterranean lineages that are unique within central Europe, suggesting long-distance dispersal or relict persistence.