Mycena lanuginosa is a species of mushroom in the family Mycenaceae. First collected in 2000 and reported as a new species in 2007, it is known only from lowland oak-dominated forests in central Honshu in Japan. The small mushroom is characterized by its grooved, grayish-brown to violet-brown cap up to in diameter, and the slender grayish-brown to reddish-brown stem covered with minute, fine, soft hairs. The mushroom produces amyloid spores (spores that stain when treated with Melzer's reagent). Microscopic distinguishing features include the smooth, spindle-shaped cheilocystidia and pleurocystidia (cystidia on the gill edge and face, respectively) and the diverticulate elements in the outer layer of the cap and the stem. Taxonomy, naming, and classification Mycena lanuginosa was first collected by Haruki Takahashi in 2000, and published as a new species in 2007, along with seven other Japanese Mycena species. The specific epithet is derived from the Latin word lanuginosa, meaning "lanugineous", referring to the hairy stem. The Japanese name for the mushroom is Keashi-haiirotake (ケアシハイイロタケ). The fungus is classified in the section Fragilipedes (Fr.) Quél., as defined by Dutch Mycena specialist Maas Geesteranus. This section is the largest in the genus Mycena. Description The cap is in diameter, conical to convex to bell-shaped, and has distinct radial grooves that extend almost to the center. It is dry, and somewhat hygrophanous (changing color as it loses or absorbs water). The surface is initially pruinose (covered with what appears to be a fine white powder), but soon becomes smooth. The cap is dark brown at the center, and gradually changes to reddish-brown and finally to nearly white at the margin. The white flesh is up to 0.5 mm thick, and does not have any distinctive taste or odor. The slender stem is long by thick, cylindrical, attached to the center of the cap, hollow, and dry. The top portion of the stem is pruinose, while near the base the surface is covered with soft, fine hairs. The stem color is grayish-brown to reddish-brown near the top, changing to reddish-brown near the bottom. The stem base is covered with long, fairly coarse, whitish fibrils. The gills are narrowly attached to the stem, distantly spaced (12–18 gills reach the stem), up to 1.5 mm broad, thin, and whitish, with the gill edges the same color as the gill faces. Microscopic characteristics The spores are roughly ellipsoid, smooth, thin-walled, colorless, and measure 10–12 by 5.5–6.5