The distribution of plant species around the Mediterranean basin is a product of the influence of both geographical barriers and of climatic changes experienced during the Tertiary, with the transition from a warm to a cool period. Several species, once largely distributed across the Northern Hemisphere, retracted to refugial areas in southern Europe where they are described as Tertiary relicts. The oriental plane tree (Platanus orientalis) is a typical representative of Tertiary flora in southwest Eurasia; distributed along river courses from the central Mediterranean to the Caucasus and India. The southern part of the Italian peninsula and Sicily represent the western border with few marginal populations, which are now threatened by human exploitation for agricultural purposes and by habitat destruction.
Quantifying the genetic diversity of species is important for understanding their evolutionary history. A recent study by Rinaldi et al. published in AoBP investigated the genetic diversity of P. orientalis, which has an unusual distribution in the Mediterranean with large populations in the east but becoming increasingly rare in the west. The authors found an overall decrease in genetic diversity from eastern to western populations, with populations in southern Italy containing the lowest levels of genetic diversity. As P. orientalis requires habitats with high moisture levels, these results provide crucial genetic information which may influence its potential to respond to environmental change and to help better understand their ability to colonize novel habitats in future changing environments.