Phylogenetic diversity of the lichenized algal genus Trebouxia (Trebouxiophyceae, Chlorophyta): a new lineage and novel insights from fungal-algal association patterns of Icelandic cetrarioid lichens (Parmeliaceae, Ascomycota)

Lichens have high tolerance to harsh environmental conditions, where lichen symbiont interactions (e.g. myco- and photobionts) may play a crucial role. The characterization of fungal-algal association patterns is essential to understand their symbiotic interactions. This study investigated fungal-algal association patterns in Icelandic cetrarioid lichens using a multi-locus phylogenetic framework, including fungal nrITS, MCM7, mtSSU, RPB1 and RPB2 and algal nrITS, nrLSU, rbcL and mtCOXII data. Most Icelandic cetrarioid lichenized fungi were found to be specifically associated to the known Trebouxia clade “S” (Trebouxia simplex/suecica group), whereas the lichen-forming fungus Cetrariella delisei forms a symbiosis with a previously unrecognized lineage of Trebouxia, provisionally named as the “D” clade. This new Trebouxia lineage is supported by maximum likelihood and Bayesian phylogenetic analyses using all four included algal loci.