Bryophytes are a dominant vegetation component of the boreal forest, and an important part of the ecosystem, yet little is known about the microbial community associated with them. The aims of this thesis were 1) to analyze the diversity of Galerina species associated with four different boreal moss species, and 2) to examine how they are distributed between the mosses’ photosynthetic versus senescent tissues. DNA sequences with affinity to Galerina were extracted from two comprehensive fungal diversity 454 pyrosequencing datasets and analyzed further. A total of 11,746 Galerina reads were clustered into 26 non-singleton OTUs that were attributed to 15 different Galerina species. Six of the Galerina OTUs were dominant and accounted for about 96% of the reads, and were found in most of the shoot fragments (>95%). Almost all the Galerina OTUs occurred more frequently in the brown senescent tissue than the green photosynthetic tissue, indicating that the OTUs are almost exclusively saprophytes. Some of the Galerina OTUs were host specific to one moss host, while others were not. This shows that the Galerina genus include species that probably are specialists to specific microniches, and also species that are non-specific generalists. This host specificity could be used as a tool to identify Galerina species apart from each other when morphological characters are very similar.