Entoloma aprile (Agaricales, Entolomataceae) new to Japan, with notes on its mycorrhiza associated with Populus maximowiczii in cool-temperate deciduous forests of Hokkaido

An entolomatoid fungus, Entoloma aprile is newly recorded from Japan. Basidiome morphology of the species is described and illustrated based on the Japanese specimens. ITS sequences were obtained from Japanese E. aprile and three related species, viz. E. clypeatum f. clypeatum, E. clypeatum f. hybridum and E. sepium. Basidiomata of E. aprile were highly homologous (99.4 % - 100.0 %) among our collected specimens and were separated from other known Entoloma spp. in the dendrogram based on ITS sequences. This results supported our morphological observation that E. aprile differed from those of allied species. Mycorrhizae of E. aprile on Populus maximowiczii in the cool-temperate deciduous forests of Hokkaido, Japan were observed by stereo, light and scanning electron microscopy for the first time. In studied mycorrhizae, the root cap, meristem, and apical region of the cortex disappeared. Fungal hyphae of the mycorrhizae invaded root tissues. Hyphal sheath outside of the cortex was composed of plectenchymatous and pseudoparenchymatous hyphae divided into three layers according to hyphal thickness and arrangement. Those morphological characteristics suggest that mycorrhizae of E. aprile are of the same type as those of allied Entoloma species associated with rosaceous and ulmaceous plants.