Armillaria Fungus Spans Over Three Square Miles in Eastern Oregon

In 2015 researchers documented an enormous fungal organism called Armillaria thriving in the forests of eastern Oregon. The network covers over three square miles (about 1,920 acres) and is estimated to weigh several thousand tons—an astonishing size for any single biological entity.¹

The discovery highlights how extensive mycelial networks can become when they persist in suitable habitats. Armillaria, commonly known as honey fungus, forms symbiotic relationships with tree roots, facilitating nutrient cycling and soil structure maintenance across vast forested areas.

Expert analysis points out that such large‑scale fungi are not singular organisms but collections of genetically identical hyphae that spread through the root systems of multiple trees. This means the observed mass may represent a long‑lived, interconnected community rather than one individual colony.

Similar cases exist elsewhere. In England, Armillaria mellea was discovered in 1937 and later found to be part of an interconnected network covering over 450 acres. These examples underscore the ecological significance of widespread fungal structures, which can endure for centuries or even millennia.