Interspecific Relationships and Origins of Taxus and Cephalotaxus

摘要

A cladistic analysis of the sequences of five chloroplast and one nuclear (ITS) molecular markers was carried out, both individually and in combination, by distance, parsimony, likelihood, and Bayesian methods. The two families are monophyletic. In Taxus, T. floridana is the first-branching taxon; T. brevifolia and T. globosa cluster together and are sister to T. baccata; the endemic T. yunnanensis clusters with T. wallichiana in subclade B and is only distantly related with the other four Taxus species in China (subclade A); T. fuana is closer to T. baccata than to other Taxus species. Torreya jackii and A. formosana are the first-branching species within Torreya and Amentotaxus, respectively. C. koreana and C. wilsoniana could be treated as two varieties of C. harringtonia. The ancestral distribution area of Taxaceae and Cephalotaxaceae is restricted either to southwest China or southeast China by DIVA analysis. The relaxed molecular clock indicates that the deepest divergences in Taxus go back to the late-Cretaceous. Our results propose interspecies relationship within each group, with profound nomenclatural and taxonomic implications. Combination of partitioned Bayesian analysis and likelihood-based methods produced a more robust phylogenetic hypothesis for the two studied families.