Using wooden cubes as experimental seed mimics we tested whether differences in seed deposition among riverbank sites predictably affect the structure of riparian vegetation. Although cube deposition was not interpretable in terms of environmental variables like current velocity, riverbank width, and substrate, it was related to species composition of the riparian vegetation. We found an excess of species with short-floating seeds among those that were most frequent in sites capturing few cubes and an excess of species with long-floating seeds among those that were most frequent in sites capturing many cubes. This result provides the first evidence that water dispersal interacting with floating time may play a role in small-scale structuring of riparian plant communities. Key words: floating time, hydrochory, riparian vegetation, river, seed mimics, seed deposition.