Phylogeny and classification of the tribe Vanguerieae (Rubiaceae)

Abstract: Vanguerieae is a tribe in the mainly tropical angiosperm family Rubiaceae. The tribe currently comprises around 600 species in 27 genera, with the major part of the species distributed in Africa south of the Sahara. The phylogeny of the tribe was investigated using both molecular and morphological data. ITS sequences of the nuclear ribosomal DNA are used in all of the included papers, and in three papers also in combination with sequences from the plastid trnT-F region and/or the rpl16 intron. Thirty morphological characters were also investigated and used in combination with molecular data. Several strongly supported groups are found, but eight of the currently recognized genera are also revealed as para- or polyphyletic, i.e., Canthium, Fadogia, Lagynias, Pachystigma, Pyrostria, Rytigynia, Tapiphyllum, and Vangueria. A new classification based on the phylogenetic analyses is suggested and a review of the morphology of Vanguerieae with a focus on taxonomically informative characters is also included. The morphologically similar Ancylanthos, Lagynias, Pachystigma, and Tapiphyllum together with a species of Rytigynia, R. fuscosetulosa, are suggested for transfer to Vangueria. All dioecious species of Vanguerieae are found to form a strongly supported group. A study of the group is performed in which all dioecious genera and also twelve undescribed species from Madagascar are included. It is concluded that the whole group should be included in Pyrostria, which necessitates transfers of Canthium subgenus Bullockia and Scyphochlamys. Canthium subgenus Afrocanthium is found to have a position isolated from the type species of the genus and it is suggested that the subgenus is given generic rank as Afrocanthium. A comparison of nuclear and chloroplast phylogenies shows that several species in a subgroup of the tribe have incongruent positions, and possible explanations for the incongruencies are discussed.