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Taxonomy and ecology of Physisporinus forming synnema-like structures in freshwater environments

ABSTRACT Since 2011, we have collected fungi that form synnema-like structures (SSs) bearing many acanthophyses at the apex on water-splashed wood in streams in various regions of Japan. A provisional phylogenetic analysis of strains isolated from SSs based on their nrDNA sequences implied affinity with Physisporinus (Polyporales, Basidiomycota). However, it has not been reported that this genus forms SSs in freshwater habitats. We found a fungus forming not only SSs on the water-boundary part of wood but also resupinate basidiocarps with poroid hymenophores on nonsubmerged parts, and the morphological characteristics of the basidiocarps matched those of Physisporinus. Therefore, we investigated the relationship between SS-forming fungi and their sexual states by taxonomic approaches. Phylogenetic analyses based on nrDNA internal transcribed spacer (ITS) and large subunit (LSU) sequences indicated that SS-forming fungi diverged into five clades in Physisporinus. Each clade was discriminated by the color of SSs, morphology of acanthophyses, and cultural characteristics. Of the five clades, Clade 1, which consisted only of sequences of strains isolated from SSs and basidiocarps produced on rhizomorphs, was closely related to P. eminens and P. undatus, but the morphology of basidiocarps and the manner of basidiocarp development differed. Clade 5 was closely related to P. castanopsidis, P. crocatus, P. pouzarii, P. sanguinolentus, P. subcrocatus, P. tibeticus, and P. vitreus, but the basidiocarp morphology differed. Therefore, Clades 1 and 5 were described as two new species. Regarding Clades 2, 3, and 4, further taxonomic studies with additional specimens are required. SS and acanthophysis formation in wet habitats in streams and in culture could be recognized as new taxonomic and ecological characters of Physisporinus. Graphical abstract