High Quality Content by WIKIPEDIA articles! 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 single organism (of the species Armillaria solidipes) covers more than 3.4 square miles (8.8 km2) and is thousands of years old. Some species of Armillaria are bioluminescent and may be responsible for the phenomena known as foxfire and perhaps will o` the wisp.