Largest bioluminescent organism

The largest bioluminescent organism is a single gigantic specimen of Armillaria ostoyae honey mushroom, discovered in the Malheur National Forest, Oregon, USA, which occupies a total area of 965 hectares (2,385 acres), equivalent to 1,350 soccer fields. The honey mushroom is well known for its glowing surface, although most of its tissue is around 1 metre (3 feet) underground, in the form of root-like mycelia.

It also holds the record for the world's largest and heaviest fungus, estimated to weigh somewhere between 7,500 and 35,000 US tons (6,800–31,750 tonnes).

Its age is calculated to be at least 2,400 years old, but may be as much as 8,650 years old.

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 fruiting bodies (i.e., mushrooms), some the root-like mycelia and in some, 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.

Of the approximate 81 known species of fungi to have exhibited the ability to bioluminesce , 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. However only 12% of Mycena species are known to bioluminesce. More colloquially, glowing mushrooms are sometimes referred to as "foxfire" or "fairy fire".