Mycena nidificata is a species of fungus in the family Mycenaceae of the Agaricales. First collected in 2000 and reported as a new species in 2007, it is known only from Kanagawa, Japan, where it grows on the floor of oak forests. The dark brown irregularly wrinkled cap measures up to in diameter. The cap is supported by a thin stem up to long, which is covered at the base by a whitish hairlike growth, and attached to white, cord-like rhizomorphs—aggregations of mycelium that resemble plant roots. The underside of the cap features thin, distantly spaced grayish gills that have distinct veins running between them. At a microscopic level, distinguishing characteristics include the inamyloid spores (turning dark blue to black when stained with Melzer's reagent), the club-shaped cheilocystidia (cystidia on the gill edges) with finger-like appendages, the diverticulate cells in the outer layer of cap and stem, and the presence of clamp connections. Taxonomy, naming, and classification Mycena nidificata was first collected in 2000 by Japanese mycologist Haruki Takahashi, and reported as new along with seven other Mycenas in a 2007 publication. The specific epithet is derived from the Latin word nidificata, meaning "nidificate"—"to make a nest". Its Japanese name is Yamiiro-kunugitake (ヤミイロクヌギタケ). According to Takahashi, the inamyloid spores, the diverticulate cap cuticle hyphae, and the dark pigment in the gill hyphae suggest that the fungus is best classified in the section Hiemales of the genus Mycena. Because of its medium-sized, partly collybioid fruit bodies (i.e., small to medium-sized with white spore prints and convex caps, similar to species once placed in the genus Collybia), the white cord-like rhizomorphs, and its distinctly intervenose gills, it has an isolated position within the section. Description The cap is initially conical to convex to bell-shaped, then flattened in age, ultimately reaching in diameter. The center of the cap is irregularly wrinkled to pitted, but less so toward the grooved margin. It is hygrophanous (changing color as it loses or absorbs water), dry, initially pruinose (covered with what appears to be a fine white powder), but soon becomes smooth. The color is blackish-brown at the center, dark brown to reddish-brown farther outward, and becoming much paler at the margin; sometimes the cap is evenly dark brown. The flesh is up to 1 mm thick and white, and does not have any distinctive taste and odor. The stem is long by wide, cylindrical, slightly enlarged