Abstract
Three species of tricholomatoid dark blue Entoloma spp. from temperate forests in Japan are described as new to science. Entoloma obscurocyaneum and E. purpureobrunneolum show a dull dark blue pileus, with the former distinguished by the purple-brown suprapellis hyphae of the pileipellis and the latter by its light brown color. Entoloma quasicyanonigrum is similar to E. cyanonigrum but exhibits smaller basidiospores. Our phylogenetic analysis placed them within a moderately supported clade that generally shares the characteristics of having a hymeniderm- or palisadoderm-type pileipellis. To date, the sole tricholomatoid dark blue Entoloma documented from Japan is E. cyanonigrum. Because it was confirmed that the type specimen of E. cyanonigrum no longer exists, the original material, the colored drawing by Tsuguo Hongo, was designated as the lectotype, and E. cyanonigrum was redescribed based on Hongo's observation notes and our examination of herbarium specimens.