New insights into the phylogenetic and biogeographic analysis of Elaeocarpus (Elaeocarpaceae) in China, and further consolidated 'Acronodia' as a distinct group.

BACKGROUND: Elaeocarpus is the most species-rich genus in Elaeocarpaceae (Oxalidales), comprising 39 species of trees that grow in tropical and subtropical forests in China, 14 of which are endemic. Few studies to focus on the phylogeny of Elaeocarpus in China. Limited available evidence indicates a close phylogenetic relationship between Sect. Ganitrus and Sect. Dicera, while the question of whether the 'Acronodia' group warrants taxonomic separation from Sect. Monocera remains unresolved. The status of group 'Acronodia' in Elaeocarpus is uncertain because the combination of molecular fragments available to construct the phylogenetic tree has not been evaluated. RESULTS: In this study, we compared chloroplast genome sequences on the basis of the alignment of 4 chloroplast genome sequences with the mVISTA and KaKs_Calculator tools. The results revealed that the phylogeny has good bootstrap value for ycf1, ITS and trnS-atpA and that 27 Elaeocarpus species (40 samples), including 3 species that are distributed naturally outside China, are grouped into 2 major clades: one comprising Sect. Ganitrus and Sect. Dicera, and the other consisting of Sect. Monocera and the 'Acronodia' group. Furthermore, the results of the phylogenetic analysis with the BEAST tool suggest that Elaeocarpus originated from Southwest China during the early Eocene (40 Ma) and started to diversify south of the Yangtze River during the early Miocene (15 Ma). CONCLUSION: Overall, this study highlights the taxonomic utility of chloroplast genomes in Elaeocarpus, and the time and regions of origin will facilitate future studies on conservation.