Phoradendron is a genus of morphologically diverse mistletoes that currently lacks a satisfactory supraspecific classification. Its subtle distinction from Dendrophthora moreover suggests that Phoradendron may not be monophyletic. This study uses sequences from three regions of the nuclear ribosomal DNA cistron to infer phylogenetic relationships in the two genera. These DNA regions differ in their rates of nucleotide substitution. Sequences of the ITS spacers are sufficiently variable to resolve relationships among closely related species but are barely alignable with those of more distantly related species and outgroups. Alignment is possible, however, among sequences of the 5.8S gene and among two regions of the 26S nuclear rDNA. Maximum parsimony analyses suggested that neither Phoradendron nor Dendrophthora is monophyletic. Three major clades were identified whose topologies suggest that many characters traditionally used for primary subdivision are homoplastic.

Communicating Editor: Alan Whittemore