XVI International Botanical Congess

Cercocarpus H.B.K. (Rosaceae) has undergone three revisions, each varying widely in the ranks assigned to taxa and the number of species. Confusion is due primarily to a continuum of morphological variation within and between taxa. We have begun to develop a molecular phylogeny to address this confusion. The ITS region of the nuclear ribosomal repeat contained insufficient phylogenetically informative sequence variation, so we developed the external transcribed spacer (ETS) of the nuclear ribosomal repeat. The ETS has more informative variation than the ITS and a unique central region that appears to divide Cercocarpus into two distinct clades. The correct taxonomic affiliation of C. traskiae, California's rarest tree, will also be addressed.