The Jack-O-Lantern mushroom, Omphalotus illudens, is a common late-summer-to-fall mushroom of the midwestern and eastern United States. It gets its common name not only because of its bright pumpkin orange color and its occurrence around the time of Halloween, but also because it can exhibit an eerie glow known as bioluminescence—the production of light by a living organism—in this case, a fungus.
Omphalotus illudens is especially appropriate here in Champaign-Urbana since it is among the few mushrooms which display the “Illini orange” color.
The Jack-O-Lantern fungus produces large clusters of mushrooms around the bases of dead hardwood trees and stumps. They can also grow from buried roots. The yellow-orange to orange cap is first convex in shape, becoming flat and then finally funnel-shaped with a margin that turns downward. Underneath the cap are found similarly-colored narrow, decurrent (running down the stalk) gills, and a pale orange, thick stalk.
Jack-O-Lanterns are attractive and have a pleasant odor, but are POISIONOUS! They are sometimes mistakenly eaten by people who think they are chanterelles. Chanterelles are similarly colored, can occur around the same time of the year, and are good edibles. However, chanterelles are smaller in stature, have gills that are not well developed (appear more like veins), and usually grow solitarily on soil.
Experiencing poisoning by O. illudens has been described as at first being afraid you’re going to die, then being afraid you’re not going to die, and finally, after several hours of abdominal pain and vomiting, you begin to feel better.
Omphalotus illudens is also one of more than 40 species of bioluminescent fungi.
The eerie light emitted by these mushrooms or by the actively growing mycelium of these fungi growing in decaying wood is a phenomenon referred to as “foxfire” and was reported as early as 382 B.C. by the Greek philosopher Aristotle.
The recognition that luminous wood was actually caused by fungi was reported in 1823, and people in the far north are reported to have marked forest trails with pieces of rotten, glowing wood to enable them to find their way back at night. It is the gills of the Jack-O-Lantern mushroom that exhibit bioluminescence. This phenomenon can be demonstrated by bringing fresh and actively growing mushrooms into a dark room at night—the darker the better. Stare at the gills of the mushrooms until your eyes become accustomed to the dark, and you may eventually see the greenish glow given off by them.
Although the reason, if there is one, that fungi glow is unknown, some suggest it functions to attract animals or insects that eat the mushroom and aid in the dispersal of its spores.