摘要Members of the genus Juglans(walnuts,family Juglandaceae)are typical Tertiary relict tree species.They are widely distributed in China and are well known for their edible nuts and high-quality wood.The genetic structure and historical gene flow patterns of Chinese Juglans still need to be resolved.Here,we collected samples from a total of 2242 trees from 142 populations of three walnut species(Juglans regia L.,Juglans sigillata Dode,and Juglans mandshurica Maxim.)and a hybrid taxon Juglans × hopeiensis.These samples were distributed throughout China.We analyzed population genetic structure,interspecific relationships,lineage differentiation,and speciation using 21 EST-SSR genetic markers.All populations of J.regia and J.sigillata clustered into one lineage,corresponding to the Juglans sect.Dioscaryon,and all J.mandshurica and Juglans × hopeiensis populations(section Cardiocaryon)clustered into a second lineage.For J.mandshurica,there was an obvious north-south genetic cline.Interestingly,except for seven populations of the hybrid Juglans × hopeiensis,there was almost no gene flow between the populations of section Juglans/Dioscaryon and section Cardiocaryon.A DIYABC analysis showed that J.regia and J.mandshurica differentiated during the Oligocene.Juglans sigillata originated during the Pliocene to the Pleistocene.Subsequently,during the Middle Pleistocene,J.regia and J.mandshurica hybridized within a narrow zone to produce Juglans × hopeiensis.These results demonstrate the impact of repeated turbulent climate changes in the Quaternary on the evolutionary history of Tertiary relict plants.