If you are asked what the largest organism in the world is, what would your answer be? A blue whale or a redwood tree? Or perhaps a giant squid? You would be wrong. But this is understandable because the world’s largest organism is largely hidden from sight and was discovered only relatively recently in 1998 in the soil of Oregon’s Blue Mountains. It is a fungus nearly ten square kilometers in area and one metre deep. It may be not only the largest single organism in the world but also one of the oldest. Based on its current rate of growth, the fungus is thought to be around 2,400 years old; however it is also possible that it has been growing for the past 8,650 years. Commonly known as the honey mushroom, the only visible evidence for the organism on the surface is groups of golden mushrooms that grow in forests during autumn.

The discovery of organism came about when Catherine Parks, a scientist at the Pacific Northwest Research Station in Oregon, heard about trees dying from root rot in a forest east of Prairie City. Using aerial photographs, she identified an area of dying trees stretching over a 5.6 kilometre area. She then collected samples from the root of these trees. When she looked at the samples, Parks were able to confirm that many of the samples were infected by the same organism; the fungus had grown bigger than any other creature known to science. A combination of good genes and stable conditions has enabled it to spread. In addition, the dry climate of the region makes it difficult for new fungi to establish themselves and compete with established fungi.

The technique of identifying the fungus was developed in 1992, when the first gigantic fungus was discovered in Michigan. A PhD biology student, Myron Smith, discovered it in a hardwood forest, when he and his team were trying to find the boundaries of individual fungi. After a year of testing, they still had not found the boundary of a particular fungus. The next things they did was develop new genetic tests to see if the DNA from the samples was from a single individual fungus and not closely related to individuals. Eventually, they realized that they had found a 1,500-year-olde fungus that weighted over 90 metric tonnes.

The honey mushroom fungus is the cause of a root disease that kills many trees in the US and Canada. It has fine filaments or tubes that grow along tree roots and connect together to form a mat. The mat then slowly consumes the food source: it produces chemicals that digest carbohydrates from the tree and interfere with the tree’s ability to absorb water and nutrients, eventually leading to the death of the host organism. As well as producing feeding filaments, the honey fungus is able to spread by producing string-like growths that reach out to find new potential food sources. The fungus spread very slowly over hundreds of years, seeking out food and killing its victims. Not surprisingly, forest service scientists are interesting in learning to control the fungus but they also realize that it has an important role to play in the forest’s ecology.

Fungi have both beneficial and harmful effects. They are essential because they decompose or break down waste matter on the forest floor and recycle nutrients. They are also central to many processes that are important to humans: they are vital to the process of making many kinds of food, including cheese bread and wine. They have been used in the production of medicines and particularly antibiotics. Even the golden mushrooms produced by the honey mushroom fungus are edible, though apparently not very tasty. On the other hand, fungi also form a major group of organism harmful to plants and animals. Some mushrooms produced by fungi, such as the death cap mushroom and the fool’s mushroom, are extremely poisonous to humans. Fungi can spoil food which has been stored, and of course they can kill trees and other plants.

Although to humans the idea of an enormous organism silently growing underground seems very strange, Tom Volk, a biology professor at the University of Wisconsin-La Crosse, explains that this may be in the nature of things for a fungus. ‘We think that these things are not very rare,’ he says. ‘We think that they’re in fact normal.’

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