Buckleya Torr. (Santalaceae) is a hemi-parasitic shrubby genus with two species in China, on in Japan, and one in the sourheastern United States. Phylogenetic relationships among these species are controversial and have not been tested using molecular data. In this study we used sequences of the internal transcribed spacer region of nuclear ribosomal DNA to test previous phylogenetic hypotheses. Two sister species pairs are well supported: B. distichophylla plus B. graebneriana, and B. lanceolata plus B. henryi. Sequence differences and morphological characters support the recognition of B. lanceolata and B. henryi. Sequence divergence between B. distichophylla and B. graebneriana is twice as high as that between B. lanceolata and B. henryi. These results are most consistent with the treatment proposed by Carvell and Eshbaugh (1982). Biogeographically, one of the Chinese species (B. graebneriana) is most closely related to the eastern North American species (B. distichophylla), while the other Chinese spcies (B. henryi) is allied with the Japanese species (B. lanceolata). Maximum likelihood analyses do not reject clock-like evolution of nrDNA ITS spacers in Buckleya, and divergence times may date to the Late Miocene and Pliocene.

Key words: Biogeography, Buckleya, ITS, Phylogeny, Santalaceae