Armillaria is a genus of 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 ostoyae") covers more than in Oregon's Malheur National Forest and is more than 2,400 years old. Some species of "Armillaria" display bioluminescence, resulting in foxfire.