Phylogenetic relationships of Combretoideae (Combretaceae) inferred from plastid, nuclear gene and spacer sequences

Phylogenetic relationships of the subfamily Combretoideae (Combretaceae) were studied based on DNA sequences of nuclear ribosomal internal transcribed spacer (ITS) regions, the plastid rbcL gene and the intergenic spacer between the psaA and ycf3 genes (PY-IGS), including 16 species of eight genera within two traditional tribes of Combretoideae, and two species of the subfamily Strephonematoideae of Combretaceae as outgroups. Phylogenetic trees based on the three data sets (ITS, rbcL, and PY-IGS) were generated by using maximum parsimony (MP) and maximum likelihood (ML) analyses. Partition-homogeneity tests indicated that the three data sets and the combined data set are homogeneous. In the combined phylogenetic trees, all ingroup taxa are divided into two main clades, which correspond to the two tribes Laguncularieae and Combreteae. In the Laguncularieae clade, two mangrove genera, Lumnitzera and Laguncularia, are shown to be sister taxa. In the tribe Combreteae, two major clades can be classified: one includes three genera Quisqualis, Combretum and Calycopteris, within which the monophyly of the tribe Combreteae sensu Engler and Diels including Quisqualis and Combretum is strongly supported, and this monophyly is then sister to the monotypic genus Calycopteris; another major clade includes three genera Anogeissus, Terminalia and Conocarpus. There is no support for the monophyly of Terminalia as it forms a polytomy with Anogeissus. This clade is sister to Conocarpus.