COMPLEX PHYLOGENETIC PLACEMENT OF ILEX SPECIES (AQUIFOLIACEAE): A CASE STUDY OF MOLECULAR PHYLOGENY

摘要

To investigate the phylogenetic relationships among Ilex species distributed in China, we analyzed two alignmentsincluding 4,698 characters corresponding to six plastid sequences (matK, rbcL, atpB-rbcL, trnL-F, psbA-trnH, and rpl32-trnL) and 1,748 characters corresponding to two nuclear sequences (ITS and nepGS). Using different partitioning strategiesand approaches (i.e., Bayesian inference, maximum likelihood, and maximum parsimony) for phylogeny reconstruction,different topologies and clade supports were determined. A total of 18 Ilex species was divided into two major groups (groupI and II) in both plastid and nuclear phylogenies with some incongruences. Potential hybridization events may account, inpart, for those phylogenetic uncertainties. The analyses, together with previously identified sequences, indicated that all 18species were recovered within Eurasia or Asia/North America groups based on plastid data. Meanwhile, the species in groupII in the nuclear phylogeny were placed in the Aquifolium clade, as inferred from traditional classification, whereas thespecies in group I belonged to several other clades. The divergence time of most of the 18 Ilex species was estimated to benot more than 10 million years ago. Based on the results of this study, we concluded that paleogeographical events and pastclimate changes during the same period might have played important roles in these diversifications.