World’s Largest Organism: The Giant Fungus Revealed | Discover Wildlife

Contrary to popular belief, the largest organism on Earth isn’t a blue whale, a giant sequoia, or even the extinct megalodon shark. It’s a fungus – specifically, a variety known as the honey fungus, Armillaria ostoyae. This single organism, often referred to as the “humongous fungus,” occupies an astonishing 2,385 acres in Oregon’s Malheur National Forest.

The concept of a fungus as the world’s largest organism challenges our intuitive understanding of size and scale. We typically associate immense size with visible structures, but the vast majority of this fungus exists hidden from view. Like an iceberg, its true extent lies beneath the surface. Mushrooms, the familiar fruiting bodies we see above ground, are merely temporary reproductive structures – analogous to the apples on a tree. The bulk of the organism is a sprawling network of thread-like filaments called mycelium, and in some cases, more specialized root-like structures called rhizomorphs.

This particular honey fungus covers an area equivalent to roughly three Central Parks in New York City, or about 3.7 square miles. To put that into perspective, its surface area is comparable to that of 18,500 adult blue whales. The discovery of its immense size wasn’t a straightforward process. It began in 1998 when over a hundred trees in the Malheur National Forest began to die. A genetic investigation, a “whodunnit” as it were, revealed that a single fungal individual was responsible for the widespread tree deaths.

Researchers determined that the fungus spreads through the soil via its rhizomorphs, actively searching for trees to consume. It then releases enzymes to break down plant cell walls, effectively feeding on the trees. A 2017 study identified a unique collection of genes within the honey fungus that facilitate this extensive growth and decomposition process.

The honey fungus, scientifically recognized as both Armillaria solidipes (named in 1900 by Charles Horton Peck) and Armillaria ostoyae (named in 1970 by Henri Romagnesi), exhibits bioluminescence. Its mycelia and rhizomorphs emit a faint green glow, known as ‘foxfire.’

Estimates place the age of this colossal fungus between 2,400 and 8,650 years old, making it not only the largest but also one of the oldest living organisms on Earth. Its indeterminate growth pattern – the ability to continue expanding as long as conditions allow – contributes to its immense size. Unlike mammals, which reach a predetermined size at maturity, this fungus continues to grow and spread, limited only by its environment.

While Armillaria ostoyae currently holds the title of the world’s largest organism, experts acknowledge that other contenders exist. Antonis Rokas, a professor of biological sciences at Vanderbilt University, notes that Antarctic blue whales, a 106-acre aspen forest, and certain hybridized eelgrass species could potentially compete for the title. However, accurately determining the true size and whether these entities constitute a single organism remains a complex challenge.

The honey fungus’s discovery highlights the hidden complexity of the natural world and challenges our conventional notions of what constitutes an individual organism. It serves as a reminder that the largest living things on Earth aren’t always the most visible.