Outline of phylogeny and character evolution in Rhizocarpon (Rhizocarpaceae, lichenized Ascomycota) based on nuclear ITS and mitochondrial SSU ribosomal DNA sequences

The phylogeny of the lichen genus Rhizocarpon (Rhizocarpaceae, lichenized Ascomycota) was investigated using nucleotide sequences from the ITS region of the nuclear ribosomal DNA and the SSU region of the mitochondrial ribosomal DNA from 13 species of Rhizocarpon, Catolechia wahlenbergii and Poeltinula cerebrina. Phylogenetic estimations were performed using maximum parsimony and Bayesian MCMC tree sampling. Twelve phylogenetic null hypotheses were tested using MCMC tree sampling. The evolution of five morphological characters was assessed by mapping them onto MCMC tree samples. The results indicate that Rhizocarpon in its current sense is polyphyletic and can only be made monophyletic if R. hochstetteri is excluded or Poeltinula, and possibly also Catolechia, are included. The root placement in the Rhizocarpaceae is ambiguous, either Catolechia or Poeltinula + R. hochstetteri being the sistergroup to the rest of the family. Previously suggested infrageneric arrangements based on presence or absence of the yellow substance rhizocarpic acid in the thallus or the septation of the ascospores are unnatural. Some species with grey or brown thallus may have evolved from a yellow ancestor. Spore septation and colour, amyloidity of the thalline medulla, and the presence of stictic acid complex and rhizocarpic acid are shown to have changed multiple times during the course of evolution. (C) 2002 The Linnean Society of London.