Bioluminescence does not only occur in many creatures of the deep sea but also, though less commonly, in land animals and plants. Diverse fungi, most of them belonging to the genus Mycena, also display bioluminescence; however, little is yet known about the purpose of their nightly glowing.
The phenomenon has arguably first been reported by Aristotle (384 BC – 322 BC), who speaks of a source of light, unlike fire, cold to the touch. And in the works of Pliny the Elder (23 AD - 79AD) we find references to decaying wood glowing in olive groves. Undoubtedly, bioluminescent shrooms have also inspired many folk and fairy tales over the centuries, and the folk names "fairy fire" and "foxfire" indicate just that. But the fairy appearances, just like the famed will-o'-the-whisps that really result from pyrophoric methane gas bubbling up from marsh lands, have a solid rooting in the soils of science: As a by-product of enzymic reactions between heterocyclic compounds called "luciferins" and certain oxidative enzymes that are subsumed under the name "luciferase", unstable chemical intermediates decompose; the excess energy released in the process can be perceived as greenish light with a maximum wavelength of 520-530 nanometers. Though most of the time the emitted light is comparably weak and adventurous wanderers through nightly forests (absence of moonlight mandatory) will have to turn off their torches and let their eyes adjust for a couple of minutes before being able to perceive the phenomenon, some claim to have read books by the light of the fairy fire, and also the first submersible ever, David Bushnell's 1775 "Turtle" that was to be deployed against the British Royal Navy during the American Revolutionary War, was illuminated by fungus-powered foxfire (the idea had come from Benjamin Franklin but was abandoned when Bushnell found, during a row of trials in November 1775, that the bioluminescent effect failed when temperatures dropped too low).
Many of the glowers look pretty unassuming during daytime; all in all, there are only 71 species of fungi to date that have been found to be bioluminescent (Dennis E. Desjardin, Mycologia, March/April, 2010), mainly in tropical rain forests. Sometimes it is the fruit bodies that will glow, at other times it is the mycelium; luminosity can vary to a great extend, also within species, depending on factors such as PH, growth temperature and diurnal periodicity. The oyster-like tree dweller Panellus stipticus, for example, is widely spread in Europe, North America, Australasia, and Asia, but only its Eastern North American strands are bioluminescent. Research could not proof any noteworthy correlation between fungal glowing properties and the attraction of spore-carrying intermediates, such as ants, so far. It has been suggested that luminescence could serve as a warning signal to fungivores, but it might as well be simply a byproduct of other metabolic processes without any further purpose. Some glowing fungi such as the chanterelle-like looking Omphalotus olearius ("Jack-o'-lantern ") and the parasitic, bleach white Omphalotus nidiformis ("Ghost Fungus") carry revealing and fanciful names, and all, with the exception of Armillaria, are poisonous.
Traditionally, glowing mushrooms have always been associated with the otherworldly, but also modern-time fantasts routinely pick up on the topic: the creators of the phosphorescent night forests in David Cameron's "Avatar", for example, were clearly inspired by the phenomenon of foxfire. In science, bioluminescent fungi could serve as indicators in toxicity testings, so called biosensors: environmental chemicals, such as soil-bound metals or organic pollutants, react with the luminescence-causing enzymes and substrates in the fungi and so can enhance or suppress light intensity ( f.i. Mendes LF, Stevani CV, http://www.ncbi.nlm.nih.gov/pubmed/20821450)