Phylogenetic Relationships of Torreya (Taxaceae) Inferred from Sequences of Nuclear Ribosomal DNA ITS Region

Abstract

Torreya, composed of five to seven species, is distributed disjunctly in easten Asia and the eastern and western United States. In this study, interspecific relationships of Torreya were examined on the basis of sequences of the nrDNA ITS region. Torreya taxifolia and T. californica of the New World form a clade, as do the Old World species. This result suggests that the previous division of Torreya into two sections does not reflect phylogenetic relationships and that the diagnostic character for the two sections, namely rumination of albumen, is homoplastic. It is possible that the present distribution of species of Torreya resulted from a single vicariance event separating the Old World and New World. However, the modern species are apparently young in age, and it will be necessary to integrate older fossils to ascertain the deeper biogeographic history of the genus.