Genetic and biometric patterns of rangewide divergence of iconic, Neogene relic broadleaved shrub species Staphylea pinnata L.– post-glacial expansion and human impact

Abstract Integrative phylogeographic studies supported by morphometric analysis and genetic data provide significant insights into the postglacial recolonization history and other factors shaping current distributions of plant species, including major forest-forming trees in Europe. However, genomic resources and phylogeographic knowledge of shrub species remain limited. Staphylea pinnata L. (European bladdernut) is a shrub native to thermophilous broadleaf forests and is the only representative of the Staphyleaceae in Central Europe. Given its historical associations with human and religious beliefs dating back to pre-Christian cultures, the current distribution of this iconic, Neogene relic species has been hypothesized to be influenced by human-assisted migration. This study aims to address this hypothesis by uncovering the genetic and morphometric relationships among S. pinnata populations across its wide distribution range in Europe, Caucasus and the Anatolian Peninsula, linking these findings with existing archaeobotanical and ethnobotanical data. We sampled 87 populations (979 individuals), genotyped them with the applications of newly developed genetic markers, and conducted morphological leafs’ measurements to estimate the postglacial expansion and human impact on the current distribution of S. pinnata . Both genetic and morphometric results indicate primarily natural post-glacial recolonization from two Pleistocene glacial refugia in the Apennines and Balkans. Additionally, we identified “suture zones” of increased genetic diversity in middle latitudes, resulting from secondary contact due to postglacial recolonization from different sources. Significant human contributions were observed towards the northernmost edge of the species’ range, including regions such as Eastern France, Lower Silesia in Poland, and Northern Podolia in Ukraine.