Molecular phylogeny and systematics of the Ocellularia clade (Ascomycota: Ostropales: Graphidaceae)

In this paper, an extended molecular phylogeny was generated for the Ocellularia clade, which includes about half of the species that were previously separated in the family Thelotremataceae. Three genes (mtSSU, nuLSU, RPB2), from a total of 270 OTUs with 136 ingroup species, were sequenced to evaluate whether the core genera, Ocellularia and Myriotrema, form monophyletic clades or split into several lineages. Further, we tested the usefulness of phenotypic characters for circumscribing monophyletic groups. Besides a maximum likelihood analysis, we incorporated the novel method of morphology-based 'phylogenetic binning', which allowed us to weight the morphological characters in those taxa with molecular data available and then predict the phylogenetic classification for over 200 additional species for which no molecular data are currently available. Our results showed that the large genera Myriotrema, Ocellularia, and Stegobolus are polyphyletic. For some of the previously unrecognized lineages, older generic names are available (Rhabdodiscus, Ocellis, Stigmagora, Antrocarpum, Macropyrenium). Some previously separated genera, such as Ampliotrema and Gyrotrema, were found to be nested within a large clade currently recognized as Ocellularia s.l. For this clade, no meaningful generic subdivision could be established based on the available data, and we proposed to recognize distinct subclades at the subgenus level. One new genus, Compositrema, was also discovered, and a second new genus, Glaucotrema, is established for the Myriotrema glaucophaenum group. Further, the genus Rhabdodiscus is reinstated formally. We found a high level of homoplasy (parallel evolution) of phenotype characters previously used for classification purposes, such as excipular carbonization, columella morphology, and ascospore size, septation, and pigmentation. Secondary chemistry, on the other hand, was remarkably uniform in most clades. Some clades also exhibit a high level of disparity of ascoma morphology. Thus, the very distinctive Gyrotrema-type apothecia occur in a clade nested within and genetically very similar to Ocellularia s.str.