Armillaria gallica (or A. bulbosa or A. lutea) is a species of honey mushroom in the order Agaricales.
The species is common and ecologically important. It decays wood. It can live as a saprophyte, or as an opportunistic parasite. In weakened trees it causes root rot.
It is found in temperate regions of Asia, North America, and Europe. The species forms the above-ground fruiting bodies "(mushrooms") in soil or rotting wood. The fungus has been accidentally introduced to South Africa.
Armillaria gallica is a largely underground fungus. The fungus develops underground root-like structures, called rhizomorphs. These help it to decompose dead wood in temperate broadleaf and mixed forests. Its ability to bioluminesce and to form large and long-lived colonies are especially interesting.