If you were asked what is the largest organism in the world, 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 meter 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 the autumn.
The discovery of the 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 kilometer area. She then collected samples from the roots of these trees. When she looked at the samples, Parks was 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 for 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 thing 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 individuals. Eventually, they realized that they had found a 1,500-year-old fungus that weighed 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.