Phylogeny and proposed circumscription of 'Breynia', 'Sauropus' and 'Synostemon' (Phyllanthaceae), based on chloroplast and nuclear DNA sequences

Abstract

Previous estimates of phylogeny in the Phyllanthaceae, Phyllantheae, have been hampered by undersampling of species from morphologically distinctive groups and using too few gene regions. To increase the phylogenetic resolution, sequences of two nuclear (ITS1-5.8S-ITS2) and 'Phytochrome C' (PHYC)) and two non-coding chloroplast (accD-psaI, trnS-trnG) DNA markers were analysed using maximum parsimony and Bayesian inference with expanded sampling in 'Breynia', 'Glochidion', 'Sauropus' and 'Synostemon'. Our results supported reinstatement of 'Synostemon', previously included in 'Sauropus s.str.', to generic rank, and provided evidence towards its future infrageneric classification. The results also indicated expansion of 'Breynia' to include 'Sauropus s.str.'; this combined monophyletic group consists of two strongly supported clades. Finally, we showed monophyly for 'Glochidion', which is sister to 'Phyllanthus' subg. 'Phyllanthodendron', both still remaining undersampled. Morphological features characteristic of 'Breynia', 'Sauropus' and 'Synostemon' are discussed, as well as the desirability of dividing 'Phyllanthus' into smaller genera.