Mericarps and pollen grains collected in the Pleistocene lacustrine deposits in Poland were analyzed. Well-developed mericarps, resembling recent fruits of water dropwort Oenanthe (Phellandrium subgenus), are found since the Eemian. Mericarps found in the Pliocene and in the Augustovian Interglacial (=Bavelian Complex or Cromerian I), in the Mazovian Interglacial (=Holsteinian interglacial) and in one of the interstadials after this interglacial are a distinct morphological type. They differ from recent mericarps of Oenanthe aquatica in shape and size. As late as the Vistulian, pollen grains are decidedly smaller and in parts with different microsculpture than recent reference material of pollen of O. aquatica. Probably, changes of vegetation in the late Pleistocene and in the Holocene could have induced changes in the composition of the pollinator assemblages, and as a consequence increase in size of pollen. Compared to mericarp evolution, the evolution of pollen of O. aquatica is somewhat delayed.