If you go out on a dark night, preferably during a new moon, in certain forests in northeastern Brazil you may find something peculiar: large glowing mushrooms. These pale-beige, slightly ruffled ’shrooms don’t look like much during the day, but at night they emit a ghostly green glimmering. They were reportedly first recorded by English botanist George Gardner in 1840, after he saw boys playing with luminous mushrooms in a Brazilian village. They were lost to science for many decades before being rediscovered in 2009, and were reclassified under their current scientific name, Neonothopanus gardneri, by researchers from San Diego State University. These fungi are one of just over 71 species of mushrooms that emit light. This makes it a very rare trait, considering there are an estimated 5 million mushroom species in total, says Jay Dunlap, a geneticist and molecular biologist at Dartmouth’s medical school. Researchers have wondered exactly why mushrooms glow, and now they think they’ve figured it out.