Mycena (Pers.) Roussel is a large genus of small saprotrophic mushrooms which comprises approximately 500 species, widely distributed in the world. It is a polyphyletic genus where comprehensive molecular analyses are needed to clarify the infrageneric classification and species circumscriptions. About 100 species have been recorded in Norway.
The size of the species varies from less than one millimeter in width up to only a few centimeters. The Mycena species are characterized by a white sporeprint, mostly a conical or bell-shaped cap, and a thin, fragile stem. They are mostly grey or brown but vary in colours from white to almost black. Some have beautiful, bright colours. The gills are attached and usually have cystidia; in some species they are coloured differently than the gill face. Some species exude a latex when the stem is broken. A few species have a distinctive smell and/or taste.
Because of the tiny size, they have no value as edible mushrooms, but a few species are known to be poisonous.
- Habit mycenoid, omphaloid, more rarely collyboid
- Cap glabrous, granular, floccose, puberulous, or pruinose, sometimes covered with a gelatinous pellicle
- Gills ascending, horizontal or arcuate; almost free or narrowly adnate to decurrent
- Stem fragile to cartilaginous or elastic-tough, in part or entirely pruinose or puberulous, or glabrous, sometimes dilated below to form a basal disc, often basally covered with long, coarse fibrils
- Basidia 2- or 4-spored
- Spores usually pip-shaped, less frequently almost cylindrical or spherical, generally amyloid, more rarely non-amyloid
- Cheilocystidia clavate, obpyriform, fusiform, lageniform, or, more rarely, cylindrical; smooth, branched or with variously shaped, simple or branched, short or rather long excrescences
- Pleurocystidia numerous, scarce or absent
- Hyphae of the pileipellis diverticulate, less frequently smooth
- Hyphae of the cortical layer of the stem smooth or diverticulate, mostly with terminal cells or caulocystidia
- Lamellar trama stainining vinaceous to purplish brown in Melzer’s reagent, in a few cases remaining unaltered
- Clamp connections present or absent