Phylogeny of Metagentiana and related genera (Gentianaceae) inferred from nuclear ribosomal ITS sequences

The infrageneric phylogeny of Metagentiana, a newly erected genus in the Gentianaceae, was constructed based on the analysis of the nucleotide sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA of 10 representative species of this genus and 22 species of Gentiana, Tripterospermum and Crawfurdia. The analysis indicates that the genus Metagentiana is polyphyletic, because all sampled species of Tripterospermum and Crawfurdia are clearly embedded within Metagentiana. The species of Tripterospermum and Crawfurdia also did not cluster respectively as two monophyletic clades. These results do not merit status of three separate genera. However, these three genera clustered together as a monophyletic clade sister to Gentiana, which is in agreement with the previous conclusions on the separation of Metagentiana from Gentiana and its closer relationship to Tripterospermum and Crawfurdia based on studies of gross morphology, floral anatomy, chromosomes, palynology and embryology. The ITS sequences do not provide sufficient information to make a robust estimation of the phylogenetic relationships among dysploid cytotypes of x=17, 21 and 23, within the Metagentiana, Tripterospermum and Crawfurdia complex, but the preliminary results seem to indicate their reticulate and paralleling evolution.