Phylogeny and Biogeography of Taxus (Taxaceae) Inferred from Sequences of the Internal Transcribed Spacer Region of Nuclear Ribosomal DNA

Abstract

Species of Taxus, particularly Taxus baccata, have long been cultivated as ornamentals in Europe and North America. Ten species of Taxus are generally recognized, but phylogenetic relationships among these species remain unclear. We used sequences of the nuclear ribosomal DNA ITS region to infer phylogenetic relationships. Three of the four New World species form a well-supported clade, within which the Pacific coastal species. T. brevifolia is sister to a clade containing T. floridana and T. globosa of northwestern Florida and northern Mexico, respectively. Taxus canadensis, which is more widely distributed in eastern North America, appears to be more closely related to Old World taxa than to other New World species. This relationship, though weakly supported in our analysis, is consistent with leaf anatomical features. Taxus chinensis and T. mairei of southeast Asia form a clade, which is sister to a clade containing T. cuspidata of Japan and northeastern China, and T. baccata of Europe and North Africa. Our ITS phylogeny implies that intercontinental disjunctions in Taxus entailed at least two vicariance events: an initial split between the New World T. floridana-T. brevifolia-T. globosa clade and the rest, and a later split separating T. canadensis from the Old World species.