World's Largest Organism Is a Fungus

Deep beneath the soil of Oregon's Malheur National Forest thrives an extraordinary organism, often called the "Humongous Fungus." This vast living entity, scientifically known as Armillaria ostoyae, is primarily hidden from view, existing as an intricate network (Review) of fungal threads. Its presence was first noted in 1988 by a Forest Service employee investigating widespread tree die-offs, and later genetic research in 1998 confirmed that a sprawling area of infected trees was actually connected by a single, colossal individual.

The immense size of this organism is attributed to its unique growth strategy. While the familiar honey mushrooms that appear on the surface are merely its fruiting bodies, the true mass of the fungus lies underground. It spreads through a vast network of mycelium, which are thread-like structures that colonize tree roots, and also via black, root-like structures called rhizomorphs, sometimes referred to as "shoestrings." These rhizomorphs allow the fungus to invade the sapwood of trees, drawing nutrients and eventually causing the trees to decay and die.

This subterranean giant covers an area of over 2,200 acres, or approximately 3.5 to 3.7 square miles, making it one of the largest known organisms on Earth by area. Its estimated age ranges from 2,400 to a remarkable 8,650 years old, suggesting it has been a silent, persistent force in the forest ecosystem for millennia. With an estimated weight that could reach up to 35,000 tons, this hidden marvel truly redefines what it means to be a single living entity.