Urban plant population genetics: A review

Modern cities are complex anthropogenic ecosystems where human activities influence ecological and evolutionary processes. These processes affect genetic diversity and gene flow of urban populations, with variable impacts depending on species’ biological traits and urban environmental constraints. This review examines the impact of urban environments on the genetics of plant populations, with a focus on the role of species' ecological traits in shaping genetic responses to urban constraints. A comprehensive analysis of existing studies challenges standard assumptions on urban ecosystems. Findings indicate that urban plant populations generally maintain genetic diversity levels comparable to those of non-urban populations. Additionally, outcrossing is not consistently reduced in cities but mainly influenced by species’ intrinsic traits. Contradicting the urban fragmentation assumption, gene flow remains high between urban populations, particularly for ruderal species dispersed on long distances by animals, including humans. Similarly, cities do not function as isolated genetic islands, since genetic exchanges persist between urban and non-urban populations. Moreover, urban plant species often maintain genetic diversity through repeated introductions and anthropogenic dispersal, while some threatened species retain a genetic structure inherited from pre-urbanization connectivity. This study highlights the complexity of interactions between urbanization and plant population genetics, challenging long-standing assumptions on fragmentation and genetic isolation in urban environments. • Urban plant populations harbor genetic diversity equivalent to non-urban ones • Plant dispersal and gene flow stay high in cities despite urban fragmentation • Species’ traits could play a key role in genetic responses in urban environments