AbstractAllelopathy (i.e. chemical interactions between plants) is known to affect individual performance, community structure and plant invasions. Yet, a quantitative synthesis is lacking. We performed a meta-analysis of 385 studies that measured allelopathic effects of one species (allelopathy plant) on another species or itself (test plant). Overall, allelopathy reduced plant performance by 25%, but the variation in allelopathy was high. Type of method affected allelopathic effect. Compared to leachates, allelopathy was more negative when residues of allelopathy plants were applied, and less negative when soil conditioned by allelopathy plants was applied. The negative effects of allelopathy diminished with study duration, and increased with concentrations of leachates or residues. Although allelopathy was not significantly related to life span, life form and domestication of the interacting plants, it became more negative with increasing phylogenetic distance. Moreover, native plants suffered more negative effects from leachates of naturalized alien plants than of other native plants. Our synthesis reveals that allelopathy could contribute to success of alien plants. The negative relationship between phylogenetic distance and allelopathy indicates that allelopathy might drive coexistence of close-related species (i.e. convergence) or dominance of single species.