Tracing back the history of introducing horse-chestnut in Europe

The horse-chestnut (Aesculus hippocastanum L.), a popular ornamental tree widely cultivated throughout Europe since the 16th century, has a very limited natural range. The work presented was intended to shed light on the human-mediated spread of this species from natural Balkan populations to artificial sites. For this purpose, chloroplast DNA (cpDNA) regions were used. We sampled 670 individuals from 83 locations, including 17 natural populations and 66 artificial stands. We detected 11 haplotypes, with haplotype I dominating in the artificial range and the northern part of the species natural range, particularly in Albania and Northern Greece. This result supports historical records suggesting initial introductions from the northern part of the Pindos Mountains to Istanbul. The results also suggest potential later episodes of introduction, probably from eastern Greece. Seven haplotypes were detected only in the natural range, indicating the isolation of particular populations. Significant reduction in genetic diversity in artificial stands compared to natural ones may suggest a founder effect during its introduction. The presented work highlights the importance of preserving genetic diversity in natural horse-chestnut populations to enhance resilience against pests and diseases. It also contributes to a better understanding of the evolutionary and ecological mechanisms of tree species colonisation, which may have implications for improving conservation strategies in the face of climate change.