What is the phylogenetic placement of Dipteronia dyerana Henry? An example of plant species placement based on nucleotide sequences

DNA sequence data have been widely used to evaluate species delimitations and examine infraspecific relationships. However, species placements inferred from different nucleotide sequences are frequently in conflict. As an example of plant species placement based on nucleotide sequences, the phylogenetic placement of Dipteronia dyerana Henry (Aceraceae) was analyzed in the present study. The study species included eight Acer species (from different sections of Acer), two Dipteronia species, and two outgroup taxa. Phylogenetic trees based on five datasets (ITS, trnL-F, trnD-trnT, psbM-trnD, and rpl16 regions) as well as their combined datasets were generated by using maximum parsimony (MP) and maximum likelihood (ML) analyses. Further analyses were conducted to compare the strict consensus trees based on single regions and the combination of different regions. The results revealed a significant discrepancy among the phylogenetic placements of D. dyerana, inferred from various sequences. Phylogenetic trees using MP analysis based on trnD-trnT, rpl16, and the four chloroplast combined sequences supported the genus Dipteronia as a monophyletic group, while in the other trees D. dyerana was positioned either in parallel with D. sinensis and Acer species or within the genus Acer. In ML analysis, only rpl16 and the four chloroplast combined sequence datasets supported the genus Dipteronia as a monophyletic group. We concluded that, although significant genetic differentiation occurred between D. dyerana and D. sinensis, D. dyerana was more advanced than D. sinensis. However, whether Dipteronia is monophyletic remains to be further investigated, e.g., by using more closely related taxa and more sequences. Furthermore, in addition to internal transcribed spacer sequences, more chloroplast gene sequences should be used for phylogenetic analyses of species.