Phylogenetic relationships within Korthalsella (Viscaceae) based on nuclear ITS and plastid trnL-F sequence data

The nuclear encoded internal transcribed spacer (ITS) region and the plasti d encoded trnL-F region were sequenced for 25 populations of Korthalsella, a genus of reduced, monoecious, Old World misletoes. The molecular study co nfirms the hypothesis that branch shape and cladotaxy (the arrangement of b ranches with respect to their parent axis) are unreliable indicators of rel ationship in the genus and demonstrates that many of the taxa previously re cognized are not monophyletic. Both gene regions identify three major subgr oups within the genus and find lower level relationships within these subgr oups highly correlated with geographic distance. An analysis based upon 18S and rbcL sequences identifies Ginalloa as the sister group to Korthalsella , which together with the branching order within the genus, indicates that Korthalsella originated in Papuasia and aids in elucidating evolution of th e peculiar inflorescence structure. There are problems associated with spec ies delimitation when evolutionary units are more restricted than morpholog ical lineages, and justification is offered for recognizing only morphologi cally diagnosable monophyletic lineages as species. Varying substitution ra tes and differing modes of inheritance in ITS and trnL-F result in compleme ntary utility of the two regions for elucidating infrageneric relationships in Korthalsella.