A treatment of Ranunculus sect. Batrachium is presented for the Eastern Alpine territory as covered by the forthcoming 4th ed. of the “Excursion flora of Austria and the entire Eastern Alps”. A newly designed key as well as alternative keys for terrestrial modificants and vegetative specimens are presented. A new outline for the section is applied including (1) the Ranunculus fluitans group (R. fluitans and R. pseudofluitans); (2) the R. trichophyllus group (R. trichophyllus, R. confervoides, and R. rionii); (3) the R. aquatilis group, including the R. aquatilis subgroup with R. aquatilis (the only member present in Europe), the R. peltatus subgroup (R. peltatus and R. baudotii) as well as related hybridogenous taxa (R. penicillatus s. str.) and (4) R. circinatus. The distribution of all species is given for the Austrian federal states, the Bavarian Alps, Liechtenstein and the South Alpine regions of Switzerland, Italy and Slovenia.