The Largest Living Organism by Biomass
Oregon’s Malheur National Forest is home to a record-breaking organism known as the Humongous Fungus, an enormous occurrence of Armillaria ostoyae. This massive fungal organism spans approximately 2,385 acres, or 3.7 square miles, making it the largest known single living organism by biomass on Earth. It resides in the Reynolds Creek and Clear Creek areas of the forest, roughly 11 miles east of Prairie City.
The Humongous Fungus is one of five distinct Armillaria ostoyae occurrences in the area, with individual sizes ranging from 50 to 2,385 acres. Discovered in 1988 by Greg Whipple, a Forest Service investigator, this colossal fungus initially appeared to cover 400 acres. Later genetic studies confirmed its immense size and unity, revealing it to weigh as much as 35,000 tons and be about 8,650 years old.
Discovery and Growth of the Fungus
The phenomenon of humongous fungi began garnering attention in 1992 when biologist James Anderson and colleagues identified a similar organism, Armillaria bulbosa, covering 37 acres in Michigan. This discovery triggered global interest in other large fungal organisms, eventually leading to the identification of the Humongous Fungus in Oregon.
Research has since uncovered the secrets behind its growth. Hungarian scientists studying Armillaria ostoyae identified genes that enable the fungus to form rhizomorphs—long, black filaments that extend underground, invading tree roots. These rhizomorphs parasitize and decay the root systems of trees, ultimately killing them and allowing the fungus to continue feeding on the dead wood. The fungus spreads slowly, advancing just 0.7 to 3.3 feet per year, and can take 20 to 50 years to kill a single tree.
Characteristics and Visibility
While most of the Humongous Fungus remains hidden underground, it produces visible honey mushrooms during the autumn months. These edible mushrooms grow in clusters at the bases of infested trees and feature gilled brown caps and white spores. Although edible, they require thorough cooking to avoid stomach discomfort. It is crucial not to mistake these mushrooms for toxic lookalikes that grow solitarily from the ground.
Infested trees exhibit specific signs, making identification possible even when the fungus is not fruiting. Dead trees often have bark peeling away, while recently killed trees display red needles. Living infected trees may show rounded tops and resin seeping from their bases.
A Global Phenomenon with Local Roots
Though the Humongous Fungus in Malheur National Forest holds the title of the largest known organism, Armillaria ostoyae is not unique to Oregon. This species is common in the Pacific Northwest and also occurs in parts of Europe, Asia, and North America. Its remarkable size and age make it a natural wonder and a testament to the resilience and adaptability of fungal life.
With inputs from Reuters
