Generic delimitation in the Cyphotheca-Plagiopetalum-Sporoxeia clade

The Cyphotheca-Plagiopetalum-Sporoxeia clade (Sonerileae, Melastomataceae) comprises Cyphotheca Diels, Plagiopetalum Rehder, Sporoxeia W.W.Sm., and some species of the highly polyphyletic Phyllagathis Blume, as well as some undescribed species, which requires taxonomic revision at the generic level. In this study, we expanded taxon sampling of the CPS clade and reconstructed phylogenetic relationships using genomic SNPs and whole plastomes assembled from genome resequencing data. We recognized six subclades in the CPS clade and observed strong cytonuclear incongruences within and among subclades. Gene tree simulation and Patterson's D-statistic indicated that the conflicting phylogenetic signals were mainly caused by incomplete lineage sorting and hybridization/introgression. Molecular and morphological divergence among species of the CPS clade were evaluated using principal component analysis. Genomic SNP data clearly separated the six subclades, whereas the boundaries of some subclades were obscure in the plots of morphological data. Through reconstruction of morphological characteristics, we found a high level of homoplasy for some characters but also identified potential synapomorphies for the lineages. Based on the results, a revised generic classification is proposed for the CPS clade. Specifically, we expand Cyphotheca, Plagiopetalum, and Sporoxeia to include additional species, and establish three new genera, namely Chiehchenii, Neophyllagathis, and Sporocyphoxeia. A description and a list of species are provided for each of the six genera. Four new species are described.