Phylogeny of Populus-Salix (Salicaceae) and their relative genera using molecular datasets

Although extensive studies have demonstrated that several genera formerly placed in the family Flacourtiaceae are the closest relatives of Populus-Salix. However, the closest relative or relatives remain uncertain due to the relatively low phylogenetic resolution and insufficient phylogenetic information. In addition, the question as to whether Populus and Salix are truly monophyletic remains open because of the absence of comprehensive studies with large-scale samples of both genera. In the present study, 54 species representing 11 genera of Salicaceae sensu lato (now including the genera of Flacourtiaceae) were studied using a combined rbcL and matK gene sequence dataset with a total length of 2134 bp, to explore the closest genera that are relatives of Populus-Salix and to determine the relationships between Populus and Salix. The resulting phylogenetic trees showed high resolution in each of the main clades. The results confirmed that (1) Idesia and Bennettiodendron are the closest relatives to Populus-Salix, followed by Poliothyrsis, and (2) Populus and Salix are a truly monophyletic lineage in which the most recent ancestor is shared by the two genera. This finding is significant for a wide variety of evolutionary studies and for understanding the classification and biosystematics of Salicaceae.