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 ca taphylls, a character used previously to distinguish the northern species from those of Central and South America. The divergent placement of P. califo rnicum rel ative 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 relati onship between P. rhipsa/inum and P. bra chystachyum, the former a parasite of conifers, renders con ifer parasitism homoplastic . A s ister group rel ationsh ip between these two species is not appare nt from morphological evidence. A clade unit ing P. serotinum, P. tomentosum, and P. velutinum was strongly supported. A broad host range characterized two of the three lineages of the basal trit omy in the northern clade, whereas the third line age united species specialized in parasitism of oaks or conifers.