The lush forests of Switzerland are not the first place that bioluminescent organisms come to mind. However, a forest in a Zurich neighborhood is home to a bioluminescent mushroom that glows green. The mushrooms newly discovered bioluminescence is described in a study recently published in the journal Mycoscience. Get the Popular Science newsletter Breakthroughs, discoveries, and DIY tips sent every weekday. By signing up you agree to our Terms of Service and Privacy Policy.What is bioluminescence?Bioluminescence is a chemical process where living organisms generate light. Jellyfish, fireflies, fungi, and more are all known to emit their very own glow. The Greek philosopher Aristotle observed bioluminescent fungi over 2,000 years ago, and he called them a cold fire emanating from decaying wood.Although the biological mechanism behind this glow is now fairly well understood, its ecological function remains elusive. Some glowing mushrooms are believed to attract insects to disperse spores, but bioluminescence occurring in parts of the fungi that are underground does not fit this hypothesis.It seems that bioluminescence has been maintained for a long time, so we assume it has some function, Renate Heinzelmann, a study co-author mycologist at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, said in a statement. But its still a mystery.[ Related: Surprise! These sea cucumbers glow. ]Finding the fungusThe mushroom was initially spotted by artists and study co-authors Heidy Baggenstos and Andreas Rudolf. The pair have been working with bioluminescent organisms for over a decade.We want to show that these bioluminescent mushrooms are present in Swiss forests and that we do not have to travel far to find them, Baggenstos said in a statement.Baggenstos and Rudolf were walking through a forest in Zurichs Albisrieden neighborhood when they spotted some green light through their camera. Similar to the northern lights, fungus natural light is sometimes so weak that it cant be seen with the naked eye and requires a camera to be visible.M. crocata growing on decaying wood. CREDIT: Baggenstos/Rudolf. Nowadays we always have our mobile phones or a flashlight, but to see bioluminescence in the forest, it has to be pitch black, said Rudolf.They collected some samples of the glowing specimen, originally thinking it was a known bioluminescent species called Mycena haematopus. In their well-lit studio, the artists realized that it was another species called the saffron drop bonnet mushroom (Mycena crocata). While this mushroom is known for its saffron-coloured milk, it had not previously been described as bioluminescent.Baggenstos and Rudolf Heinzelmann to further characterize the discovery. The artists first used long exposure photographs and a luminometera device that amplifies weaker light more than a camera doesto measure how much light is emitted by different parts of the mushroom.Most of the experiments were conducted by the artists, said Heinzelmann. They collected the samples, took the photographs, and made the light measurements.An underground glowIn fungi, the key step towards bioluminescence occurs when the enzyme luciferase converts light-emitting compound called luciferin into an unstable product. This conversion then releases energy in the form of light when it decays. Unlike with fluorescence, this process does not need an external source of light.The light measurements showed that the recognizable fruiting body of M. crocata that stands apart from the stipe base, is non-luminous. Instead, the fungis myceliumthe underground network of filaments similar to plant roots that absorb nutrientsis the most bioluminescent. As a result, the decaying wood M. crocata grows on can also glow green when it is split open. This green glow can last up to four hours when the wood typically dries. When Baggenstos and Rudolf grew pure mycelia cultures, they remained bioluminescent for up to 164 days in optimal conditions.Bioluminescence is sometimes observed at the base of the mushrooms stipe. CREDIT: Baggenstos/Rudolf. Heinzelmanns Genetic experiments confirmed the species identity and the presence of bioluminescence-related genes in all of the fungi of the Mycena genus that glow.There will constantly be more bioluminescent species discovered, Heinzelmann predicts, Bioluminescence is under-researched, and the more people look, the more they will find.