Genetically based phenotypic differentiation between native and invasive populations of exotic plants has been increasingly documented and commonly invoked to explain the success of some invasive species. Nonetheless, this basic information is lacking for invasive trees although they currently represent a major concern worldwide. Reciprocal common gardens were therefore set up in both native and introduced ranges of two exotic maple trees to assess the contribution of genetic differentiation and phenotypic plasticity to tree invasiveness. Almost 3,000 native and invasive seedlings of Acer negundo and Acer platanoides were planted in Canada and in France and their performances were compared in various life-history traits related to growth, leaf phenology and ecophysiology over 2 and 3 year periods. Invasive populations of A. negundo exhibited strong genetic differentiation in all the traits examined. Compared to their native conspecifics, they grew significantly larger in the introduced range and showed lower survival, reduced maximum assimilation rate and increased leaf area in the two gardens. They also expressed greater plasticity for growth and greater phenological sensitivity to temperature. Native and invasive populations of A. platanoides were plastic across environments but in contrast did not exhibit any genetic differentiation. This cross-continental comparison provides evidence that both genetic differentiation and phenotypic plasticity contribute synergistically to tree invasiveness. The influence of these respective processes depends on stage of invasion and the life-history strategy of each species. Plastic effects are likely more important during colonization and establishment whilst genetic effects may contribute more significantly during the spread of established populations.