Phylogeography of the oriental plane tree uncovers ancient colonization routes across the mediterranean basin

Abstract

Aim: The oriental plane tree is a Tertiary relict species with a fragmented range across southeastern Europe and southwestern Asia, forming a key component of riparian forest vegetation. Despite its ecological and cultural importance, the evolutionary history of this tree species has remained unclear, particularly regarding the relative contributions of ancient and more recent climatic events to its present distribution. Location: Southeastern Europe and Southwestern Asia. Time Period: Cenozoic. Taxon: Platanus orientalis L. (Platanaceae). Methods: We attempted the first plastid genome-based phylogeographic analysis of the species across its native range, coupling phylogenomic evidence with molecular dating to reconstruct its evolutionary history. Results: Mediterranean Anatolia was identified as the primary center of origin and diversification of P. orientalis, with basal Anatolian lineages underpinning an ancient east–west expansion across the Mediterranean Basin. Crete retains a high diversity of deeply divergent haplotypes, consistent with long-term persistence and underscoring the role of large Mediterranean islands as refugia for paleo-endemic lineages. By contrast, southern Italian accessions show reduced plastid diversity and close affinities with West Balkan lineages, indicating more recent colonization. The absence of isolation-by-distance suggests that geographic distance alone does not account for the observed genetic structure in P. orientalis. Main Conclusions: Long-term isolation, insularity, and limited dispersal likely shaped both deep lineage divergence and present-day genetic structure in P. orientalis. This makes the species a survivor of the Tertiary flora and an important biogeographic record of Mediterranean paleogeographic and paleoclimatic history, with clear implications for conserving evolutionarily distinct relict lineages under ongoing climate change.