By KATE JAIMET

An old oak tree grows on a grassy wedge of land at the corner of Hillsdale Road and the Rockcliffe Parkway. Scott Redhead, curator of the National Mycological Herbarium, heads there in late summer to pick the orange mushrooms that sprout beneath the tree. He takes his harvest to a pitch-black room where he will witness a curious phenomenon: the aptly named jack-o’-lantern mushrooms will glow with an eerie blue-green light. It’s one example of bioluminescence, the subject of the blockbuster Creatures of Light exhibit opening this month at the Canadian Museum of Nature.

’Shroom Search

Around the world, many creatures make their own light, from backyard fireflies to deep-sea fish. But if you’re hunting for glow-in-the-dark mushrooms in the Ottawa area, the jack-o’-lantern — known scientifically as Omphalotus illudens — is one of three fungi to look for. The other two are commoner but more difficult for a non-expert to identify: the off-white penny-sized Panellus stipticus and the yellow-brown Armillaria ostoyae, also known as the honey mushroom.

FoxFire in the Forest

Panellus stipticus mushrooms cluster on rotting stumps and branches. Take a branch of them home, head to a dark room, and wait 10 minutes to see them gleam blue-green around the gills. In the case of Armillaria ostoyae, it’s not the body of the mushroom that shines, but a mass of microscopic filaments called the mycelium. The mycelium penetrates a living or dead tree and causes the wood to give off a ghostly glow, known in folklore as foxfire.

How & Why

How do fungi create their own light? Broadly speaking, it’s the result of a chemical reaction involving oxygen. Although luminescent mushrooms were recorded as far back as the time of Aristotle, scientists still don’t understand the exact process. Nor do they know why the mushrooms shine. Perhaps the light attracts insects, which spread the spores of the mushrooms. Perhaps it’s a warning that the mushrooms are poisonous. Or perhaps it’s simply a by-product of other life processes, with no purpose of its own.

Stuff of Legends

Shining mushrooms and glowing trees appear in legends around the world, from the Anglo-Saxon Beowulf to the Japanese folk-tale collection Konjaku-monogatari. It’s interesting to speculate what stories of ghosts, fairies, and will-o’-the-wisps have been inspired over the centuries by the spooky gleam of mushrooms in the woods. Perhaps the burning bush of the Old Testament, unconsumed by the fire within it, was not a supernatural miracle, but merely the phosphorescence of a humble fungus.