Towards a complete phylogeny of African Melastomateae : systematics of Dissotis and allies (Melastomataceae)

Abstract

Dissotis has long been regarded as the most species-rich genus of African Melastomataceae, yet its diagnostic characters have never been examined in an explicitly phylogenetic context. In a previous study, we recovered a large clade consisting of “Dissotis and allies” but with poorly understood generic limits. Here we present a nearly complete phylogeny of African Melastomateae with focus on Dissotis and allies using sequences generated from two nuclear (nrETS, nrITS) and two plastid markers (ndhF, psbK-psbL), sampling 94 accessions representing 69 species including outgroups. We infer phylogenetic relationships using maximum likelihood, parsimony and Bayesian approaches and propose a revised generic classification of Dissotis and allies based on our molecular trees. In addition, we reconstruct the ancestral state of 20 important morphological characters of African Melastomateae. Dissotis and Antherotoma as previously circumscribed are polyphyletic, while all four of the previously recognised sections of Dissotis subg. Dissotis are monophyletic (i.e., sections Dissotis, Macrocarpae, Sessilifoliae and Squamulosae). We also recovered a clade consisting of D. congolensis, A. senegambiensis, A. clandestina and Nerophila gentianoides plus the species earlier treated in African Osbeckia. Ancestral character reconstruction indicates there are no unambiguous morphological synapomorphies for Dissotis s.l. In particular, the character of staminal dimorphism is shown to be homoplasious. However, the individual clades making up Dissotis and allies are each diagnosed by one to several morphological characters. In view of these results, we propose the following changes for the classification of African Melastomateae: (1) five new genera are described, Almedanthus (for Dissotis pachytricha), Eleotis (for D. sect. Sessilifoliae), Feliciotis (for D. sect. Macrocarpae), Pyrotis (for D. gilgiana) and Rosettea (for D. sect. Squamulosae); (2) the genus Nerophila is reinstated with an expanded circumscription to include Antherotoma senegambiensis, A. clandestina, D. congolensis, D. pauciflora and three species earlier treated in African Osbeckia; (3) circumscription of Dissotis s.str. is reduced to six species; (4) the monospecific genus Derosiphia is reinstated; and (5) two species previously placed in Dissotis are transferred to Antherotoma. To complete our generic realignment, 12 new synonyms and 58 new combinations are effected at or below the species level. A total of 40 lecto- or neotypes are designated. A revised key is provided for African Melastomateae, including all nine genera presently recognised in Dissotis and allies. Dissotis leonensis (type and only species of D. subg. Paleodissotis) together with the monospecific Cailliella and Dionychastrum remain unsampled.