Taxonomic and ecological significance of synnema-like structures/acanthophyses produced by () species.

, a genus in , , is a versatile fungus that lives as a wood decomposer, a potential pathogen of standing trees, and an orchid mycobiont. We previously reported that some species inhabiting wet wood in aquatic environments such as streams and waterfalls form synnema-like structures (SSs) bearing acanthophyses at their apices, and that they produce acanthophyses on vegetative hyphae when cultured on agar media. In this study, we investigated the acanthophysis-forming ability in and allied genera, and experimentally demonstrated the function of SSs. Phylogenetic analyses and observations of , and cultures showed that all of the strains forming acanthophyses belonged to , whereas strains of and did not produce acanthophyses. These findings suggest that SS/acanthophysis formation is a useful taxonomic character for members of . When strains were cultured under oxygen (O) concentrations of 5, 10, 20 and 40%, most of those cultured under 20% O formed the most acanthophyses. According to these experimental data, the SSs/acanthophyses in were considered to have a respiratory function. probably acquired the SS/acanthophysis-forming ability to adapt to moist and/or aquatic habitats and to decay wet wood in which the O concentration is often low.