Armillaria

Honey fungus, or Armillaria or оpenky (Ukrainian:опеньки), is a genus of parasitic fungi that live on trees and woody shrubs. It includes about 10 species formerly lumped together as A. mellea. Armillarias are long lived and form some of the largest living organisms in the world. The largest organism (of the species Armillaria solidipes) covers more than 3.4 square miles (8.8 km) in Malheur National Forest and is more than 2,400 years old. Some species of Armillaria display bioluminescence, resulting in foxfire.