Phylogeny of section Leuce (Populus, Salicaceae) inferred from 34 chloroplast DNA fragments

• Section Leuce is monophyletic and contains two sister clade.
• P. tremula L. has a closer affinity to P. davidiana Dode than other species.
• P. tremuloides is sister to P. grandidentata.
• The phylogeny of section Leuce was fully recovered using a sufficient dataset.

Section Leuce Duby (Populus, Salicaceae) is an important taxon among the 6 sections in the genus Populus. Although biological and taxonomic studies has greatly improved our understanding of this section, the phylogenetic relationships among the species of section Leuce remain uncertain due in part to the limited number of loci for analysis. In the present study, 34 chloroplast DNA fragments, which included 22 new chloroplast DNA fragments as well as 12 chloroplast DNA fragments used previously, were applied to explore interspecific relationships in this section. The inclusion of additional chloroplast DNA fragments recovered a well-resolved phylogeny of section Leuce. According to our phylogenetic tree, (1) we can confirm the monophyly of section Leuce and two sister clade subdivisions; (2) P. tremula L. shows closer affinity to P. davidiana Dode than other species, which has previously been a source of debate; (3) P. tremuloides Michx. and P. grandidentata Michx. form sister subclades; and (4) we propose that the previously unresolved phylogeny of section Leuce is most likely due to insufficient data. Our phylogenetic analysis successfully resolved the phylogeny of section Leuce using a sufficient dataset. This study provides an important foundation for evolutionary studies and for the effective utilization of the wild germplasm resources of section Leuce.