Why Some Mushrooms Glow in the Dark

Neonothopanus gardneri mushrooms definitely look better in the dark. Cassius V. Stevani

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.

Dunlap and colleagues from the University of São Paulo in Brazil have shown in a new study that the mushrooms emit light only during the night, with a peak intensity occurring about 10 p.m. This corresponds to a period of high activity among flies and flying insects, which congregate near these glowing mushrooms, Dunlap says. The scientists think that this is beneficial for the mushrooms because when the insects land on and brush up against the fungi, they pick up its spores and then spread them to new places when they fly elsewhere. Spores can then germinate when they land in other suitable locations.

"Bioluminescence is a tool the mushrooms use to make themselves interesting to insects, which take their spores place to place," Dunlap says.

Light on time

The scientists also showed that fake mushrooms illuminated with a green light, similar to that of N. gardneri, attracted many times more insects than non-illuminated dummy 'shrooms.

Some scientists have argued that the mushrooms glowed as a byproduct of their natural metabolism, but the new study discounts that, showing that they produce this bioluminescence only during nighttime and can metabolize normally, breaking down cellulose, without emitting light. In the study, published in the journal Current Biology, the scientists show that the light is carefully controlled by the fungi's biological clock.

This is a fascinating study that clears up long-held questions, says Brazilian researcher Etelvino José Henriques Bechara, who wasn't involved with the project. Glowing fungi have been known since the time of Aristotle, who wrote about them in his work De Anima. But as to why they did it, that has never been more firmly established than it is now in this paper, he says.

He was particularly interested in the fact that the fungi glow according to a nightly schedule, peaking at 10 p.m.

"If I lived [among the mushrooms], I could use the light intensity to tell time," he says.

N. gardneri mushrooms growing on the base of a young babassu palm in northeastern Brazil. Michele P. Verderane/IP-USP-2008