Most diverse bioluminescent fungus

Of the approximate 81 known species of fungi to have exhibited the ability to bioluminesce (i.e., generate their own light), at least 68 belong to the genus Mycena. This means that this group of mushrooms represents 84% of all known bioluminescent fungi, as reported in a study published in the journal PNAS (Proceedings of the National Academy of Sciences) on 8 December 2020.

The genus Mycena, commonly known as bonnet mushrooms after their bell-shaped fruiting bodies, contains some 600 species and is distributed in woodland and forests around the world. More than 10% of Mycena species are known to bioluminesce. More colloquially, glowing mushrooms are sometimes referred to as "foxfire" or "fairy fire".

Bioluminescent fungi are relatively little studied, although they have been documented for millennia, by notable historical figures such as Aristotle (384–322 BCE) who described such eerie organic light as "a cold fire". Different parts of the fungus glow with a green light in different species: in some, it's the basidiocarp (i.e., mushrooms), some the root-like mycelia and in some, as is the case with Mycena, it can be both. Recent research has shown that fungal bioluminescence is the result of a chemical reaction between luciferin, a luciferase enzyme, and molecular oxygen and works in a not dissimilar way to how a firefly generates light, albeit taking a slightly different route. The best theory currently as to why some fungi bioluminesce is to attract insects that help to spread the spores of the mushroom.

Other genera of fungi to exhibit bioluminescence include certain species of bitter oyster (Panellus, part of the wider Mycenaceae family), jack o'lantern mushrooms (Omphalotus) and honey mushrooms (Armillaria); the latter includes the world's largest living organism, a specimen of A. ostoyae that occupies an area of 965 hectares (2,385 acres), equivalent to 1,350 soccer fields, in the Malheur National Forest of Oregon, USA.