Invasive species often pose significant threats to biodiversity and ecosystems, yet the evolutionary mechanisms driving their range expansion and invasiveness remain poorly understood. This study focuses on Phalaris arundinacea L., an invasive wetland grass, and examines how multiple, uncontrolled introductions of genetic material from different European regions have influenced its evolutionary potential in North America. The genetic diversity in the European range of reed canarygrass has been reshuffled and recombined in North American populations, leading to the emergence of novel genotypes. This process has alleviated genetic bottlenecks, particularly in peripheral populations, and increased genetic diversity and heritable phenotypic variation compared to the native range. The resulting high evolutionary potential has enabled rapid selection of genotypes with enhanced vegetative colonization ability and phenotypic plasticity, contributing to the grass's aggressive expansion in North America. Repeated introductions of a single species can inadvertently create harmful invaders with high adaptive potential, allowing them to evolve in response to changing climates and have increasing impacts on native communities. Multiple immigration events may trigger future adaptation and geographic spread by preventing genetic bottlenecks and generating genetic novelties through recombination. The study highlights that the invasive potential of reed canarygrass in North America is an evolved feature resulting from these introductions. The genetic and phenotypic differences between invasive and native populations, along with higher phenotypic plasticity in invasive populations, suggest that natural selection plays a significant role in their success. The findings emphasize the importance of considering immigration history in invasive species management, as repeated introductions can lead to unintended evolutionary outcomes and increased invasiveness.Invasive species often pose significant threats to biodiversity and ecosystems, yet the evolutionary mechanisms driving their range expansion and invasiveness remain poorly understood. This study focuses on Phalaris arundinacea L., an invasive wetland grass, and examines how multiple, uncontrolled introductions of genetic material from different European regions have influenced its evolutionary potential in North America. The genetic diversity in the European range of reed canarygrass has been reshuffled and recombined in North American populations, leading to the emergence of novel genotypes. This process has alleviated genetic bottlenecks, particularly in peripheral populations, and increased genetic diversity and heritable phenotypic variation compared to the native range. The resulting high evolutionary potential has enabled rapid selection of genotypes with enhanced vegetative colonization ability and phenotypic plasticity, contributing to the grass's aggressive expansion in North America. Repeated introductions of a single species can inadvertently create harmful invaders with high adaptive potential, allowing them to evolve in response to changing climates and have increasing impacts on native communities. Multiple immigration events may trigger future adaptation and geographic spread by preventing genetic bottlenecks and generating genetic novelties through recombination. The study highlights that the invasive potential of reed canarygrass in North America is an evolved feature resulting from these introductions. The genetic and phenotypic differences between invasive and native populations, along with higher phenotypic plasticity in invasive populations, suggest that natural selection plays a significant role in their success. The findings emphasize the importance of considering immigration history in invasive species management, as repeated introductions can lead to unintended evolutionary outcomes and increased invasiveness.