Two new Mycena section Calodontes species: One newly discovered and the other new to Japan.

ABSTRACT

In 2017, two candidate species of Mycena were reported from Japan, with the Japanese names "Togari-sakura-take" and "Mitsuhida-sakura-take". However, to date, no taxonomic study or formal description has been undertaken for these two species. In the present study, we conducted comprehensive morphological and molecular phylogenetic examinations of "Togari-sakura-take" and "Mitsuhida-sakura-take", and compared them to known species within the genus Mycena. We performed phylogenetic analyses on a concatenated dataset, including the internal transcribed spacer region of ribosomal RNA, RNA polymerase II largest subunit, and translation elongation factor-1 alpha genes. "Togari-sakura-take" formed a clade with Mycena subulata, which was recently described from China, whereas "Mitsuhida-sakura-take" formed a distinct independent clade. We identified the former as M. subulata based on molecular phylogenetic analyses and morphological observations. However, the Japanese specimens displayed dextrinoid cheilocystidia and caulocystidia as well as the inamyloidity of basidiospores, which differed from the original description of M. subulata based on the materials from China. "Mitsuhida-sakura-take" was characterized by its remarkably dense lamellae and could be distinguished from known Mycena species by the combination of absent pleurocystidia and presence of bowling pin-shaped cheilocystidia. Here, we describe "Mitsuhida-sakura-take" as a new species, named Mycena densilamellata, in the section Calodontes.