The Caucasian corticioid fungi: level of endemism, similarity, and possible contribution to European fungal diversity

We assess the composition of corticioid fungi in the Caucasus region for the first time. The Caucasian corticioids were compared with those of well-documented areas in the Northern Hemisphere using the Tripartite similarity index and cluster analysis. To investigate the significance of the Caucasus region as a possible contributor to the colonization of wood-inhabiting basidiomycetes in Europe, DNA sequences of nuclear ribosomal internal transcribed spacers (ITS1 and ITS2) belonging to the corticioid fungus Peniophorella praetermissa were analysed for comparisons of genetic diversity within and differentiation between geographical regions. Putative species endemism and disjunction of corticioids in the Caucasus region is also discussed. The composition of corticioid fungi in the Caucasus region was found to be distinctly more similar to Europe and North America than to East Asia and India. Similarity tests and molecular Fsts both point to a strong connection between the Caucasus and Europe. The highest molecular diversity in P. praetermissa was in the Caucasus and East Asia as compared with other regions studied. The Caucasus and East Asia were significantly differentiated from each other, and unlike Caucasian samples, East Asian sequences were highly divergent from the European ones. This result suggests that the Caucasus might have been a source of colonization for Europe. Endemism is very low, possibly a common feature for wood-inhabiting saprotrophic fungi.