Abstract Because plants are mostly sessile, dispersal of pollen and seeds during reproduction determines changes in gene frequencies within populations and plant distributions on a broader scale. Selection favours a mixture of local and distant dispersal and for nearly all plants this is achieved with a single type of dispersal structure because dispersal is relatively ineffective on average whatever the dispersal mode; this ineffectiveness probably accounts for the rarity of dimorphic dispersal structures. Empirical studies show that most dispersal is local, but far-dispersal events, because of their potential to increase fitness though colonisation of unoccupied habitat patches, are probably what largely determines the selection of dispersal structures. The effectiveness of dispersal can be described in terms of distance, and the ability to reach favourable habitats. Effectiveness in achieving distance, a result of the interaction of the dispersal mode and agent with the environment, results in the typical leptokurtotic dispersal curve. There is no evidence that the shape of the dispersal curve itself is selected.