Genetic diversity and species delimitation of the zeorin-containing red-fruited Cladonia species (lichenized Ascomycota) assessed with ITS rDNA and β-tubulin data

Zeorin-containing red-fruited Cladonia species, the so-called C. coccifera group, are widespread terrestrial lichens which share most of their secondary substances but differ morphologically. The main objective of this study was to explore whether the current delimitation of these species is supported by molecular data. A total of 52 European and North American specimens of C. coccifera, C. deformis, C. diversa, and C. pleurota were examined. The internal transcribed spacer regions of the nuclear ribosomal DNA and the beta-tubulin gene loci were sequenced for phylogenetic analyses. Traditional morphological species circumscriptions in zeorin-containing members of the C. coccifera group are not supported by molecular data. Cladonia coccifera, C. deformis, and C. pleurota were recovered as polyphyletic in both gene topologies; C. diversa formed a lineage in the ITS phylogeny but this was not statistically supported. We detected chemical patterns of the presence/absence of porphyrilic and/or isousnic acid which may help to characterize two lineages. Our results also show incongruence between the two molecular markers studied. Therefore, we focused on possible explanations of this phenomenon. Five major evolutionary mechanisms can potentially result in phylogenetic discordance between genes: presence of pseudogenes, horizontal gene transfer, gene paralogy, incomplete lineage sorting, and hybridization. These mechanisms are briefly discussed. We consider incomplete lineage sorting and/or hybridization to best explain the incongruence.