The fungus Cenococcum geophilum Fr. (Dothideomycetes, Ascomycota) is one of the most common ectomycorrhizal fungi in boreal to temperate regions. A series of molecular studies has demonstrated that C. geophilum is monophyletic but a heterogeneous species or a species complex. Here, we revisit the phylogenetic diversity of C. geophilum sensu lato from a regional to intercontinental scale by using new data from Florida (USA) along with existing data in GenBank from Japan, Europe, and North America. The combination of internal transcribed spacer (ITS) ribosomal DNA and the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene resolved six well-supported lineages (87-100 % bootstrap values) that are closely related to each other and a seventh lineage that is phylogenetically distinct. A multi-locus analysis (small subunit (SSU), large subunit (LSU), translational elongation factor (TEF), and the largest and second-largest subunits of RNA polymerase II (RPB1 and RPB2)) revealed that the divergent lineage is the sister group to all other known Cenococcum isolates. Isolates of the divergent lineage grow fast on nutrient media and do not form ectomycorrhizas on seedlings of several pine and oak species. Our results indicate that C. geophilum sensu lato includes more phylogenetically distinct cryptic species than have previously been reported. Furthermore, the divergent lineage appears to be a non-mycorrhizal sister group. We discuss the phylogenetic diversity of C. geophilum sensu lato and argue in favor of species recognition based on phylogenetic and ecological information in addition to morphological characteristics. A new genus and species (Pseudocenococcum floridanum gen. et sp. nov.) is proposed to accommodate a divergent and putatively non-mycorrhizal lineage.
Keywords: Anamorph; Dothideomycetes; Ectomycorrhiza; Glonium; Pseudocenococcum; Species complex.