MycoKeys 2019 4;50:1-77. Epub 2019 Apr 4.
Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, 405 30 Göteborg, Sweden.
is an ectomycorrhizal, corticioid fungus whose name is frequently assigned to collections of basidiomata as well as root tip and soil samples from a wide range of habitats and hosts across the northern hemisphere. Despite this, its identity is unclear; eight heterotypic taxa have in major reviews of the species been considered synonymous with or morphologically similar to , but no sequence data from type specimens have been available. With the aim to clarify the taxonomy, systematics, morphology, ecology and geographical distribution of and its morphologically similar species, we studied their type specimens as well as 147 basidiomata collections of mostly North European material. We used gene trees generated in BEAST 2 and PhyML and species trees estimated in STACEY and ASTRAL to delimit species based on the ITS, LSU, Tef1α and mtSSU regions. We enriched our sampling with environmental ITS sequences from the UNITE database. We found the group to contain 13 molecularly and morphologically distinct species. Three of these, , and , are already known to science, while ten species are here described as new: , , , , , , , , and . We discovered and to form a sister clade to all other species in s.l. These two species, unlike all other species in the complex, are dimitic. In this study, we designate epitypes for , and and lectotypes for and . We show that the holotype of and the lectotype of are conspecific with , but in the absence of molecular information we regard and as doubtful taxa due to their aberrant morphology. We confirm , and as excluded taxa, since their morphology clearly show that they belong to other genera. A key to the species of the group is provided. We found to be a common species with a wide, Holarctic distribution, forming ectomycorrhiza with a large number of host species in habitats ranging from tropical forests to the Arctic tundra. The other species in the group were found to be less common and have narrower ecological niches.