To understand the evolutionary consequences of hybridization between the outcrossing plant Geum rivale and the selfer G. urbanum we tested the predictions of two simple models which assume either A). low or B). high pollen fitness in hybrids. Model A predicts only four genotypic classes (G. rivale, G. rivale backcross (BCR), F1 and G. urbanum) and asymmetric introgression from inbreeding to outbreeding species. Model B predicts additional genotypic classes and potential generation of novel inbreeding lines in the hybrid swarm. AFLP analysis of adults revealed only the four genotypes predicted by model A. However, microsatellite analysis of parent-progeny arrays demonstrated production of selfed offspring by F1 and BCR maternal parents and contribution of these genotypes to outcross pollen pools, as predicted by model B. Moreover AFLP and morphological analysis showed that the offspring generation comprised genotypes and phenotypes covering the entire spectrum of variation between the two parental species, in line with model B. A common garden experiment indicated no systematic reduction in fitness of offspring derived from hybrid parents. The genetic structure of the adults in the Geum hybrid swarm cannot be explained by restricted mating patterns but may result from ecological selection acting on a diverse offspring population.