Fungus Is the Largest Living Organism

When picturing Earth's most massive lifeforms, blue whales or towering sequoias often come to mind. The true titleholder, however, lives almost entirely out of sight. The colossal honey fungus in Oregon is not a single giant mushroom, but a vast, interconnected network (Review) of fungal threads called mycelium. The small, honey-colored mushrooms that occasionally sprout above ground are merely the organism's temporary fruiting bodies, akin to a single apple on an enormous, hidden tree. The vast majority of its biomass weaves through the soil and tree roots across nearly four square miles.

This "Humongous Fungus" was identified when researchers investigated a large-scale die-off of trees in the Malheur National Forest. They hypothesized that a single pathogen was responsible. To confirm this, they collected samples from various locations across the affected area and analyzed their DNA. The results were astounding: the genetic tests proved that the samples, taken from distant points, all belonged to one continuous, clonal organism that had been slowly growing and spreading for thousands of years.

This ancient giant sustains its immense size by acting as a powerful parasite (Review). It sends out tough, black, shoelace-like structures called rhizomorphs that travel through the soil, infecting the root systems of trees and draining them of nutrients. This process, which causes a fatal condition called Armillaria root rot, allows the fungus to methodically consume entire sections of forest over millennia, making it a slow-moving but relentless force of nature.