Armillaria gallica is a species of honey mushroom in the family Physalacriaceae. It is a common and ecologically important wood-decay fungus that can feed on dead organic material in soil, or live as an opportunistic parasite in weakened tree hosts to cause root or butt rot. It is found in temperate regions of Asia, North America, and Europe. The yellow-brown mushrooms, covered with small scales, can grow to around 10 cm (4 in) in diameter. On the underside of the caps are gills that are white to creamy or pale orange. The fungus has been the subject of considerable scientific research into its role as a plant pathogen, its ability to bioluminesce, its unusual life cycle, and its ability to form large and long-lived colonies. A 1,500-year-old colony was discovered in the early 1990s in a Michigan forest, reported to cover an area of 15 hectares (37 acres) and weigh at least 9,500 kilograms (21,000 lb); as a tourist attraction called the "humungous fungus", it inspires an annual mushroom-themed festival in Crystal Falls. (Full article...)