Armillaria, is a genus of parasitic fungi that includes the A. mellea species known as honey fungi that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as A. mellea. Armillarias are long-lived and form some of the largest living organisms in the world. The largest known organism (of the species Armillaria solidipes) covers more than 3.4 square miles (8.8 km2) in Oregons Malheur National Forest and is more than 2,400 years old. Some species of Armillaria display bioluminescence, resulting in foxfire.