Molecular phylogeny of tribe Forsythieae (Oleaceae) based on nuclear ribosomal DNA internal transcribed spacers and plastid DNA trnL-F and matK gene sequences.

The tribe Forsythieae comprises 2 genera (Forsythia and Abeliophyllum) and 14 species distributed mostly in the Far East. Although Forsythieae is considered monophyletic, with many symplesiomorphic characters, the phylogenetic status of Abeliophyllum remains controversial. We assessed the phylogenetic relationships of Forsythieae, based on a 3.3-kb plastid fragment (trnL-F region and matK gene) and nuclear internal transcribed spacer (ITS) region DNA sequences. We obtained a highly resolved and strongly supported topology with possible outgroups. The topology of the combined tree was congruent with those of the ITS region and matK gene. Maximum parsimony, maximum likelihood, and Bayesian inference tree analyses for the combined data also yielded identical relationships. Combined sequence data strongly supported the monophyly of Forsythieae and the close relationship between Fontanesia and Jasminum. Oleaceae, not Fontanesia, was found to be a sister group to Forsythieae. Moreover, the genus Abeliophyllum was distinctly independent of Forsythia. Three Forsythia lineages were suggested: (a) ONJ (ovata-nakaii-japonica clade), (b) VGE (viridissima-giraldiana-europaea), and (c) KISS (koreana-intermedia-saxatilis-suspensa). Our results indicated that F. × intermedia is not a hybrid between F. suspensa and F. viridissima, but further studies are needed to determine its taxonomic identity. Furthermore, the diverse fruit shapes in Oleaceae are assumed to be the result of parallelism or convergence.