Phylogenetic relationships within subfamily Arbutoideae (Ericaceae) were estimated using parsimony and maximum likelihood analyses of sequence data from the ITS region and part of the large subunit of nuclear ribosomal DNA. The data support the monophyly of Arctostaphylos, Arctous, and Comarostaphylis, but suggest that Arbutus is not monophyletic, with Mediterranean Basin species more closely related to the clade containing Arctostaphylos, Arctous, Comarostaphylis, Ornithostaphylos, and Xylococcus than to the western North American species of Arbutus. Calibration of branch lengths with the fossil record suggests that a vicariance event occurred among members of the Arbutoideae between western North America and the Mediterranean Basin at the Paleogene/Neogene boundary, consistent with the Madrean-Tethyan hypothesis.

Communicating Editor: Kathleen A. Kron