Molecular phylogeny of Enkianthus Lour. (Ericaceae) based on chloroplast and nuclear DNA sequences with an emphasis on the origin of polyploid species

Enkianthus is a small genus of Ericaceae mostly in east Asia, most constituent species with important ornamental and ecological values. Due to limited sampling of Chinese species and neglect of the origin of polyploid species in previous studies, phylogenetic relationships within this genus remain elusive. Using six chloroplast DNA fragments (psbA-trnH, rpl32-trnL, trnL-trnF, rps16-trnQ, psbJ-petA and matK), nuclear ribosomal internal transcribed spacer (nrITS) and one single-copy nuclear gene (OG9899), we reconstructed the phylogenetic relationships of most Enkianthus species, with a special attempt to decipher the origin of polyploids within the genus. The phylogenetic trees excluding polyploid species indicated that the sections of Meisteria, Andromedina and Enkianthus were all monophyletic groups, with sect. Enkianthus first branching out. The position of E. tubulatus was in conflict between cpDNA and nuclear gene trees, indicating that this species could be of hybrid origin. After the inclusion of polyploid species, we found that members of sect. Enkiantella clustered either with sect. Meisteria or with sect. Andromedina in nuclear gene trees, suggesting this section might be derived from allopolyploidy. The close affinity of sect. Enkiantella with sect. Meisteria in cpDNA tree implies that the members of sect. Meisteria might be the maternal progenitor of sect. Enkiantella. In addition, the octoploid species E. campanulatus might be either an autopolyploid or an allopolyploid with one of its progenitors originating from sect. Meisteria. Our findings provide a robust phylogenetic framework for the evolutionary study and the utility of germplasm resources of Enkianthus. The results of this study will also be helpful for the breeding of Enkianthus cultivars.