Beneath the Blue Mountains of eastern Oregon, a single honey fungus has been silently spreading through the forest for millennia, covering nearly 10 square kilometers. This organism, known as Armillaria ostoyae, is one of the largest living things on Earth, but its true size and age are still debated. The fungus is mostly hidden underground, with only the occasional dying tree and seasonal mushrooms betraying its presence. It's a fascinating example of nature's resilience and adaptability, but it also raises important questions about how we define and measure life.
The fungus was first spotted in the Malheur National Forest in 1988 by a Forest Service worker, Greg Whipple. At the time, he estimated its extent at about 400 acres, but further research revealed that this was a vast underestimate. Genetic testing and mapping techniques showed that the entire organism was a single individual, covering an area of approximately 9.6 square kilometers. This is not the only Armillaria in the forest, but it is the largest and most notable patch, as it is all part of a single organism.
Armillaria ostoyae exists primarily as mycelium, a network of fine threads called hyphae that spread through soil and wood. It also grows rhizomorphs, tough root-like strands that allow it to travel from one tree root to the next. The fungus advances by killing trees, with the dead and dying trees forming a map of its spread. The autumn mushrooms, which release spores and give the fungus its name, are the only visible part of the organism.
Estimating the age of the fungus is challenging, as it has not been carbon-dated or counted for rings. However, researchers have used the spread rate of Armillaria to estimate its age, placing it between 1,900 and 8,650 years old. Even the lower end of this range makes it an ancient organism, and the upper end would place it among the oldest living things known. The weight of the fungus is also difficult to measure, with estimates ranging from several thousand tonnes to perhaps 35,000 tonnes.
The title of the largest living organism on Earth is hotly contested. While the Oregon fungus is often called the largest, it may no longer hold this title. A single seagrass clone in Shark Bay, Western Australia, covers roughly 200 square kilometers, and a quaking aspen clone in Utah, known as Pando, is estimated to weigh around 6,000 tonnes. However, the definition of what constitutes a single organism is also important. The fungus, seagrass, and aspen are all considered single genets, genetically identical cells physically connected and spreading by cloning. This definition allows them to be considered as single individuals of extraordinary size.
Despite the debate over its title, the Armillaria ostoyae in Oregon is a remarkable organism. It has been growing outward from a single point for at least 1,900 years, killing trees as it goes, and it is a testament to the resilience and adaptability of nature. The argument over its title is more about words than the fungus itself, which is a fascinating and enduring part of the natural world.
