Hidden diversity of marine borderline lichens and a new order of fungi: Collemopsidiales (Dothideomyceta)

The fungal genus Collemopsidium comprises species that develop so-called borderline lichen symbioses with algae or cyanobacteria. Together with morphologically similar pyrenocarpous fungi it has been assigned to the family Xanthopyreniaceae. The adscription of this family to higher taxonomic ranks remain uncertain. Using sequence data of five nuclear genomic regions (nuLSU, nuSSU, tef1-alpha, rpb1 and rpb2) and one mitochondrial locus (mtSSU) we found that the studied representatives of this family are placed in the Dothideomyceta, yet relationships with the classes Dothideomycetes and Arthoniomycetes remain uncertain. We describe the new order Collemopsidiales to accommodate the genus Collemopsidium (paraphyletic as currently understood) and the lichenicolous genus Zwackhiomyces. Using five fungal fossils as calibrations points, we infer an age of c. 230 Mya for the crown of Collemopsidiales. Based on two molecular markers, we also provide insight into the global diversity of marine species of the genus Collemopsidium. According to the species delimitation algorithm GMYC, c. 26 putative species exist, far more than the six species recognized hitherto. We have confirmed this result by comparing the two alternative species models by means of Bayes factors, using path sampling and stepping-stone sampling algorithms to estimate the marginal likelihood of each model. Finally, our observations suggest rock-boring ability evolved in parallel in the different lineages within this group of fungi.