Mycena cinerella, commonly known as the mealy bonnet, is an inedible species of mushroom in the family Mycenaceae. It is found in Europe and the United States, where it grows in groups on fallen leaves and needles under pine and Douglas fir. The small grayish mushrooms have caps that are up to wide atop stipes that are long and thick. Its gills are grayish-white and adnate, with a "tooth" that runs slightly down the stipe. The fungus has both two- and four-spored basidia. As its common name suggests, it smells mealy.
First called Agaricus cinerellus by Finnish mycologist Petter Karsten in 1879, he transferred it to the genus Mycena that same year. In his 1936 Flora Agaricina Danica (Agaric flora of Denmark) Jakob Emanuel Lange referred it to the genus Omphalia; Omphalia cinerea (P. Karst.) J.E. Lange is now a synonym. Mycena cineroides was named and described as a new species distinct from M. cinerella by Hintikka in 1963, who thought it to be unique due to its narrowly acute cap that lacked brownish or yellowish tones, decurrent gills, and two-spored basidia. However, intermediate forms of it have been found, and some authorities, like Dutch Mycena specialist Maas Geesteranus, believe it should be treated as a synonym of M. cinerella.
The mushroom is commonly known as the "mealy bonnet". The specific epithet cinerella means "somewhat ashy color".
The cap of M. cinerella is white and small, with a diameter typically ranging from . Initially , conic, and then convex, it expands during maturity, developing visible grooves on the surface that correspond to the gills underneath the cap. The cap has a broad, flattened umbo. The cap surface is smooth and moist, with a slimy margin that is initially pressed against the stipe; with age the margin becomes notched and sometimes scalloped, turning translucent. The cap color is dark gray to pale gray, somewhat hygrophanous, fading to ashy white or brown when dry. The flesh is thin, gray, and tough, with a strongly (mealy, similar to raw potatoes) odor and taste if crushed or chewed. The whitish to grayish gills are moderately broad (2âÂÂ3 mm) with a spacing that is close to subdistant, and 18âÂÂ26 reach the stipe, interspersed with two or three tiers of lamellae (short gills that do not extend fully from the cap margin to the stipe). The stipe attachment is or , but later develops a pronounced tooth. The decurrent tooth occasionally separates from the stipe, forming a collar around it. The stipe is long, thick, equal in width throughout, hollow, cartilaginous, and brittle. The stipe surface is smooth or polished, with the apex initially faintly (as if covered with a fine whitish powder). The base of the stipe is sparsely covered with sharp, straight, stiff hairs, and is the same color as the cap or paler. The mushroom is inedible.
The spores are 7âÂÂ9 by 4âÂÂ5 üm, , smooth, and amyloid (reaction very weak in some collections). The basidia (spore-bearing cells) are four-spored, or occasionally a combination of two- and four-spored. The four-spored forms have clamp connections that are absent in the two-spored forms. The (cystidia found on the face of the gills) are not differentiated. The (cystidia found on the edges of the gills) are embedded in the hymenium and inconspicuous, measuring 22âÂÂ36 by 5âÂÂ11 üm. They are roughly (like thin filaments), with numerous contorted branches or protuberances, and club-shaped with finger-like prolongations. The flesh of the gills is , and turns vinaceous-brown when stained in iodine. The flesh of the cap has a well-differentiated , with a differentiated but not very well-developed hypoderm, and hyphae that are 10âÂÂ20 üm wide.
Mycena cinerella is a saprobic fungus, that derives nutrients by decomposing leaf litter and similar detritus, converting it to humus and mineralizing organic matter in the soil. The fruit bodies grow in groups on needles under pine and Douglas fir, typically in the late summer and autumn. In the United States, it has been collected from Michigan, Washington, Oregon, and California. In Europe, it has also been collected from Great Britain, Norway, Poland, and Sweden.