Omphalotus olearius

Omphalotus olearius, the jack-o'-lantern mushroom, is a striking bright orange to yellow-orange wood-rotting fungus that fruits in dense clusters on or above buried hardwood. It is best known for two things: its bioluminescence — fresh fruiting bodies emit a faint green glow, brightest from the gills — and its toxicity. It is a poisonous gastrointestinal irritant and one of the most frequent causes of mushroom poisoning, largely because foragers mistake it for edible chanterelles.

History

The species name olearius and the synonym illudens ("deceiving") both point to the mushroom's long association with olive groves and with fooling foragers. Its eerie nighttime glow — a form of natural luminescence also called foxfire — has been noted since antiquity; Pliny the Elder remarked on a luminous agaric growing on trees that could be found by its own light at night. Across cultures the glow gave rise to folklore, and the autumn brightness of the gills lends the mushroom its Halloween-evoking common name. Despite its beauty it has been documented repeatedly as a poisoning agent, including mass poisonings of foragers who took it for chanterelles.

Overview

Ecologically, Omphalotus olearius is a white-rot decomposer that breaks down lignin and cellulose in dead and buried hardwood, and its bioluminescence is thought to be a byproduct of this wood-decay metabolism. It is common in North America in late summer and early fall and also occurs in southern Europe and the Middle East, often around olive trees. While the mushroom is poisonous, its sesquiterpene compounds — chiefly illudin S and illudin M — have drawn pharmacological interest: illudin S inspired the semi-synthetic anticancer agent irofulven, which has been studied in clinical oncology trials. Key identifying features are the clustered growth on wood, uniform bright orange coloration, true sharp decurrent gills, white spore print, and the green glow of fresh specimens.