A honey fungus in Oregon may be the largest living thing on Earth, sprawling across miles

Beneath a stretch of Oregon’s Malheur National Forest, a single organism has been quietly expanding for thousands of years without ever breaking the surface in any obvious way. It is a fungus, not a plant or animal, and it covers ground more than a hundred times the size of the largest known animal colonies, making it one of the strongest candidates anywhere for the title of the largest living thing on the planet. Almost none of its bulk is visible; the vast majority survives as thread-like filaments spreading through soil and tree roots, only occasionally sending up the small honey-colored mushrooms that give it away each autumn.

Nearly 2,400 Acres of a Single Organism

The specimen in question, a fungus called Armillaria ostoyae and nicknamed the Humongous Fungus, occupies the Reynolds Creek and Clear Creek areas of the forest roughly eleven miles east of Prairie City, Oregon, according to the Oregon Encyclopedia, a project of the Oregon Historical Society. Genetic testing determined that the colony spans 2,385 acres, about 3.7 square miles, making it one of five separate and genetically distinct Armillaria ostoyae occurrences identified in that section of the forest, the smallest covering only about 50 acres. A summary on Wikipedia citing Forest Service documentation puts the organism’s estimated weight at up to 35,000 tons, a figure that has led some accounts to describe it as heavier than nearly any animal that has ever lived, blue whales included.

An Underground Search Triggered by a Michigan Discovery

The Oregon find did not happen in isolation. In 1992, biologist James Anderson and two colleagues determined that a colony of a related species, Armillaria bulbosa, in a Michigan hardwood forest was a single organism covering 37 acres, a discovery that made international headlines under the same “humongous fungus” label and set off a broader search for even larger specimens. That search eventually reached the Malheur National Forest, where Forest Service employee Greg Whipple first investigated an Armillaria infestation in 1988; initial estimates put the affected area at around 400 acres before more thorough genetic testing revealed the colony actually spanned the full 2,385 acres now on record. A separate Michigan specimen studied more recently by researchers, described in reporting cited on Wikipedia, was estimated at roughly 2,500 years old and 440 tons, a mass equivalent to about three blue whales, illustrating just how much larger the Oregon organism is by comparison.

A Slow-Moving Killer of Douglas Fir and Grand Fir

What makes the Oregon organism so large is not rapid growth but patience measured in centuries. Long, black, shoestring-like filaments called rhizomorphs extend from the fungus through the soil at a rate of only 0.7 to 3.3 feet per year, according to the Oregon Encyclopedia, invading the roots of susceptible conifers, most commonly grand fir in the Malheur forest, and parasitizing them from below. It can take twenty to fifty years for the fungus to kill an individual tree outright, and the organism continues feeding on the dead wood long after, which lets it accumulate territory over a span the Oregon Encyclopedia estimates at roughly 8,650 years. Foresters can spot the damage aboveground through resin flow at the base of infected trees, thinning or discolored crowns, and the telltale white mycelial fan that appears beneath the bark of a dying tree.

Genetics, Not Guesswork, Confirmed a Single Organism

Calling the Oregon fungus a single living thing rather than a cluster of related but separate fungi rests on genetic research rather than visual inspection, since almost the entire organism is invisible underground. Researchers in Hungary later grew Armillaria ostoyae in laboratory conditions and identified the genes responsible for building its rhizomorphs, tracing them to genetic pathways that, in other fungi, are used to grow mushroom stems, according to the Oregon Encyclopedia’s account of that work. Genotyping is also what confirmed the boundaries of the five distinct Malheur colonies in the first place, distinguishing genetically identical tissue that had spread from a common origin from neighboring fungal growth that only looked similar above ground. A USDA blog post on the discovery notes the fungus has since become something of a minor tourist curiosity, drawing visitors curious to stand above an organism they cannot actually see.

An Edible Mushroom With an Outsized Reputation

Despite its menace to the forest’s conifers, the fungus is not dangerous to people in the way its “humongous” nickname might suggest. Each fall, the organism fruits into honey mushrooms, typical gilled, brown-capped fungi that grow in clusters at the base of infected trees and are generally considered edible once well cooked, though the Oregon Encyclopedia cautions that some people experience stomach upset and warns against confusing them with toxic lookalikes that grow singly rather than in clumps. Land managers treat the fungus primarily as a forestry problem rather than a public hazard, replanting disease-affected stands with more resistant species such as western redcedar or ponderosa pine, since the fungus can persist in cut stumps for up to fifty years and chemical treatments have proven neither effective nor cost-efficient against an organism this deeply rooted.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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