Emily Johnson
The biggest mushroom in the world is a matter of perspective. If we are talking about the largest individual fruit body, then a specimen discovered in Hainan Island, China, takes the crown. This 20-year-old mushroom was estimated to weigh between 400 and 500 kilograms. However, if we are talking about the largest fungal colony, then Armillaria ostoyae, also known as the humongous fungus, takes the cake. This organism spans 3.5 square miles in Oregon's Malheur National Forest and may weigh up to 35,000 tons, making it one of the largest known organisms in the world by area.
| Characteristics | Values |
|---|---|
| Name | Armillaria ostoyae (synonyms: Armillaria, Armillaria solidipes, honey mushrooms) |
| Location | Malheur National Forest, Strawberry Mountains, eastern Oregon, USA |
| Size | 3.5 square miles (2,200 acres; 9.1 km2) |
| Weight | 35,000 tons |
| Age | 8,000 years |
| Type of fungus | pathogenic species of fungus in the family Physalacriaceae |
| Appearance | Cream-brown colour, prominent cap scales, and a well-developed ring |
| Habitat | Grows and spreads primarily underground, with honey mushrooms appearing as surface fruits in the autumn |
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What You'll Learn
Armillaria ostoyae: the world's largest single living organism
The Armillaria ostoyae, commonly known as the honey mushroom, is the world's largest single living organism. This giant fungus was first discovered in 1992 by Terry Shaw of the US Forest Service and Ken Russell, a forest pathologist. It covers a vast area of 2.5 square miles (6.5 square kilometres) in southwestern Washington. In 2003, Catherine Parks of the USFS in Oregon and her team discovered an even larger specimen of Armillaria ostoyae, spanning 2,384 acres or 3.5 square miles (6 square kilometres). This particular fungus is believed to be the largest fungal colony in the world and is estimated to be 2,400 years old, with a possible age of up to 8,650 years.
The Armillaria ostoyae is a formidable organism that can survive by digesting living tree roots. This ability has allowed it to thrive beneath the forest floor, feasting on the trees in its path. Its longevity is remarkable, having survived in the same spot for nearly 10,000 years. Despite its massive size, the fungus is mostly underground and only becomes visible during its reproductive phase when the mushroom cap appears.
The honey mushroom is not just impressive for its size but also for its resilience. It produces rhizomorphs, which are particularly robust structures that can soak up minerals from the soil and even withstand most fungicides. This fungus plays a dual role in the ecosystem: on the one hand, it can be beneficial by pruning maladapted trees and returning nutrients to the soil; on the other hand, it can become a bringer of death to fragile trees when human actions disturb the natural balance.
The discovery of the Armillaria ostoyae has sparked debates about the definition of an individual organism. Scientists use genetic tests and molecular genetic techniques to distinguish individual fungi from their closely related siblings. Despite its immense size, the Armillaria ostoyae in Oregon may not be a single organism, as there is uncertainty about whether all parts of the mycelium are connected. Nevertheless, this fungus is a true marvel, showcasing nature's boundless diversity and the intricate relationships between organisms in our ecosystems.
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Oregon's 'humongous fungus'
Oregon's Humongous Fungus, scientifically known as Armillaria, is believed to be the largest single living organism on Earth. Located in the Malheur National Forest in the Strawberry Mountains of eastern Oregon, the fungus covers 2,385 acres, about 3.7 square miles. It is estimated to weigh as much as 35,000 tons and may be 8,650 years old.
Armillaria is a parasitic fungus that reproduces sexually. It grows and spreads primarily underground, sending out black fibres called rhizomorphs or "shoestrings" that invade the roots of trees. The trees fight back, oozing out of holes in the bark, but often succumb to the fungus. Armillaria fruits in the fall, producing what are commonly known as honey mushrooms, which grow in clumps out of the base of infested trees. These honey mushrooms are typical gilled brown mushrooms with stalks two to four inches tall and caps two to five inches across. They are considered edible but can cause stomach distress for some and need to be well cooked.
The discovery of Armillaria in Oregon was preceded by a similar find in Michigan. In 1992, biologist James Anderson and his colleagues discovered an occurrence of Armillaria bulbosa in a hardwood forest in northern Michigan, comprising a single organism covering 37 acres. This discovery set off a worldwide search for other instances of humongous fungus, leading eventually to the Oregon discovery.
Despite its immense size and parasitic nature, Armillaria plays a beneficial role in the ecosystem. As a decomposer, it prunes maladapted trees and returns their nutrients to the soil, aiding in the recycling of dead trees back into the soil. Birds also benefit from the presence of Armillaria, as they use the cavities of dead trees for nesting. However, human actions, such as logging and climate change, have contributed to the growth of Armillaria, as these activities create more vulnerable trees for the fungus to infect.
The age and size of Oregon's Humongous Fungus are impressive, and it is unlikely that human intervention will have much impact on it. It is a part of the natural landscape and a testament to the resilience and complexity of fungal organisms.
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Honey mushrooms
The largest known honey mushroom organism (of the species A. ostoyae) covers more than 3.4 square miles (8.8 km2) in Oregon's Malheur National Forest and is estimated to be 2,500 years old. This makes it the biggest individual recorded honey mushroom, but other giant specimens have been documented, including one on Michigan's Upper Peninsula.
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Rhizomorphs
The development of rhizomorphs begins with a submerged thallus that produces mycelium (hyphae biomass). When deprived of nutrients and exposed to increasing oxygen levels, morphogenesis occurs, giving rise to pseudo or microsclerotia (survival structures of some fungi), which precede rhizomorph development. Concentrations of oxygen play a crucial role in their production; when there is a high concentration of oxygen in the atmosphere, along with soil moisture, temperature, and pH, rhizomorph production increases.
While some rhizomorph-forming fungi are saprophytes, living on decomposing organic material, others can be plant enemies. The bootlace fungus (Armillaria mellea) is a major cause of root rot, infecting healthy trees and contributing to their decline. However, some rhizomorph-producing fungi can also be plant allies, forming symbiotic relationships and delivering water and nutrients to plants in exchange for carbohydrates.
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Armillaria gallica
The name Armillaria gallica was given by French mycologist Henri Romagnesi and Helga Marxmüller in 1987. The specific epithet "gallica" refers to the type locality, which is France. The species was previously known as Armillaria bulbosa, a name now considered a synonym, along with A. lutea.
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Frequently asked questions
The largest fungal colony in the world is the Armillaria ostoyae, also known as the "humongous fungus", which spans 3.5 square miles (9.1 square kilometres or 2,200 acres) in eastern Oregon's Malheur National Forest. It is estimated to be 8,000 years old and may weigh up to 35,000 tons.
Armillaria ostoyae is a pathogenic species of fungus in the family Physalacriaceae. It is also known as Armillaria solidipes and is often referred to as a "honey mushroom".
Armillaria ostoyae grows and spreads primarily underground, invading the sapwood of trees and disseminating over large distances under the bark or between trees in the form of black rhizomorphs, also known as "shoestrings". Low competition for land and nutrients allows this fungus to grow to huge proportions.
Yes, a specimen of Armillaria gallica found near Crystal Falls, Michigan, covers 91 acres (0.37 square kilometres or 0.142 square miles). Another large fungus was discovered in Hainan Island, China, in 2008 by Bao-Kai Cui and Yu-Cheng Dai. This specimen, which was 20 years old, weighed between 400 and 500 kilograms.
A mushroom colony, or fungal colony, is a group of mushrooms that are all part of the same organism. These colonies can cover very large areas and are formed by a network of connected fruit bodies, known as sporocarps or mycelia.
