Infrageneric phylogeny of the genus Gentiana (Gentianaceae) inferred from nucleotide sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA

The internal transcribed spacers (ITSs) of nuclear ribosomal DNA have been sequenced for 20 species of Gentiana. By incorporating previously released sequence data of eight species, phylogenetic analyses using Fitch parsimony and character-state weighted parsimony were carried out. The length of ITS1 in the taxa surveyed ranged from 223 to 238 bp and ITS2 from 216 to 234 bp. Sequence divergence between pairs of species ranged from 5.0% to 48.9% in ITS1, from 1.1% to 45.3% in ITS2, and from 3.2% to 46.1% in combined data of lTS1 and ITS2. The ITS phylogeny was generally congruent with morphological classifications except that G. asclepiadea was revealed to be closely related to section Gentiana instead of section Pneumonanthe and section Stenogyne was shown to be a paraphyletic group of the genus Gentiana that would be better excluded from the genus. A divergence among the three European endemic sections and the remaining sections of the genus other than section Stenogyne was revealed. Thus the European species of the genus together do not form a monophyletic group. A close relationship between the sections Chondrophyllae s. 1. (including section Dolichocarpa), Cruciata and Pneumonanthe was suggested. The section Frigidae s. 1. (including sections Monopodiae, Isomeria, Microsperma, and Phyllocalyx) contained two well-supported clades: section Frigidae s. str. and all others together. The monophyly of the typically dysploid group section Chondrophyllae s. 1. was confirmed. Optimization of chromosome numbers on the ITS phylogeny suggested that 2n = 26 is a plesiomorphic state for the clade comprising sections Frigidae s. 1., Cruciata, Pneumonanthe, and Chondrophyllae s. 1., and probably 2n = 20 is a plesiomorphic state for the dysploid group, section Chondrophyllae s. 1.