Phylogeny of the complex Vanguerieae (Rubiaceae) genera Fadogia, Rytigynia, and Vangueria with close relatives and a new circumscription of Vangueria

The phylogeny of the Vanguerieae genera Fadogia, Rytigynia, Vangueria, and closely related genera is investigated using nuclear rDNA ITS sequences and plastid trnT-F and rpl16 sequences. Individual and combined analyses reveal several strongly supported clades. There are indications that Fadogia, Rytigynia, Tapiphyllum, and Vangueria are para- or polyphyletic and only Multidentia is strongly supported as monophyletic. Several taxa are found to have incongruent positions in the ITS and chloroplast phylogenies, and possible reasons behind these incongruencies are discussed. For Ancylanthos rubiginosus a chloroplast capture event can explain the incongruent position. In the Fadogia-Rytigynia group the incongruence is more widespread and cannot be attributed to a single taxon or a few taxa, but hybridization and introgression is the most likely explanation for the incongruence. It is concluded that the genera Ancylanthos, Lagynias, Pachystigma, and Tapiphyllum and the three species Fadogia agrestis, Rytigynia fuscosetulosa, and Rytigynia induta should be transferred to Vangueria.