Phylogenetic Relationships in Phoradendreae (Viscaceae) Inferred from Three Regions of the Nuclear Ribosomal Cistron. II. The North American Species of Phoradendron
A parsimony analysis based on sequences from the ITS region and two partitions of the 26S subunit of nuclear ribosomal DNA was used to infer phylogenetic relationships among the North American species of Phoradendron. A strongly supported clade united all but one of the species typically lacking cataphylls, a character used previously to distinguish the northern species from those of Central and South America. The divergent placement of P. californicum relative to the members of this northern clade confirmed the hypothesis that species lacking cataphylls are polyphyletic. Four of five species parasitic on conifers formed a well-supported clade. However, a strongly supported relationship between P. rhipsalinum and P. brachystachyum, the former a parasite of conifers, renders conifer parasitism homoplastic. A sister group relationship between these two species is not apparent from morphological evidence. A clade uniting P. serotinum, P. tomentosum, and P. velutinum was strongly supported. A broad host range characterized two of the three lineages of the basal tritomy in the northern clade, whereas the third line age united species specialized in parasitism of oaks or conifers
