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.