The Humongous Fungus of Oregon

Beneath the surface of Oregon's Malheur National Forest lies a remarkable living entity that challenges our perception of the largest organisms on Earth. This vast, mostly unseen life form, a species of fungus known as Armillaria ostoyae, is often referred to as the "humongous fungus." The bulk of this organism exists as a sprawling underground network (Review) of mycelial threads, the fungal equivalent of roots. This single genetic individual spans an impressive 2,385 acres, or approximately 3.7 square miles, and is estimated to weigh as much as 35,000 tons.

The incredible size of Armillaria ostoyae stems from its unique growth strategy. It spreads through black, root-like structures called rhizomorphs, which extend silently through the soil, seeking and infecting hosts. These rhizomorphs allow the fungus to obtain nutrients over vast distances by penetrating tree roots. It acts as both a saprotroph, breaking down dead matter, and a pathogen, capable of killing living trees, especially conifers. This dual nature fuels its indeterminate growth, with scientists estimating this ancient organism has been growing for up to 8,650 years.

The "humongous fungus" gained widespread recognition following its discovery in 1988, with its true extent confirmed through extensive genetic testing in the 1990s