Soar above northeastern Oregon and you’ll notice circles of lifeless conifers punctuating the canopy, resembling cigarette burns in a carpet. For years, foresters documented these circles as distinct occurrences of root disease. However, sampling eventually revealed that they were all marks left by a single organism beneath.
This organism is a honey fungus, Armillaria ostoyae, sprawling over 965 hectares of the Malheur National Forest located in the Blue Mountains. This equates to 9.65 square kilometers, or 2,385 acres, which is roughly equivalent to 1,665 football fields, as pointed out by Scientific American. Almost entirely underground, the only visible aspect from above is the trees it devastates.
Identifying one fungus from another
The figure originates from fieldwork conducted in 1998 and 1999 by a group of researchers, including Brennan Ferguson and USDA Forest Service scientist Catherine Parks, and was published in the Canadian Journal of Forest Research in 2003. They collected 112 samples from the roots of dying and dead conifers across approximately 16,100 hectares of dry mixed-conifer woodland and then had to determine how many distinct fungi were present.
Their technique, somatic incompatibility, sounds more complex than it is. They grew two samples towards each other in a dish and observed the interaction at the boundary. Different strains halted, declined to blend, and formed a dark line between them. Cells from the same organism merged and continued as if nothing happened.
Sixty-one of the samples fused together.
These 61 originated from trees separated by distances up to 3,810 meters. Four other genetically unique individuals were discovered in the same forest area at distances of 20, 95, 195, and 260 hectares, making the large one remarkable even by the norms of its own kind.
The age is a calculation, not a birth certificate
How do you ascertain the age of something that lacks rings or a birth certificate?
The age is derived through division: halve the maximum diameter to calculate a radius, then divide by the known rate of fungal spread through soil. Published growth rates for A. ostoyae vary from 0.22 meters per year to about one meter, prompting the team to calculate three different estimates, yielding ages of 1,900 years, 2,200 years, and 8,650 years. The commonly cited age of 2,400 years falls towards the more conservative end of the range. Ferguson and his co-authors labeled their own method cautious, as uneven growth from the original infection site would likely inflate the actual age.
Regardless of the exact figure, this entity has been replicating itself for millennia with minimal variation. Geneticists who sequenced a 2,500-year-old Armillaria specimen in Michigan for Proceedings of the Royal Society B discovered its mutation rate to be remarkably low. This is just one study of one fungus in a related group, so consider it a suggestion rather than a rule. James Anderson, who led the research, highlighted the contrast with cancer, which mutates rapidly and destabilizes itself. This organism behaves conversely, continuously persisting.
What is actually observable
The truthful answer is very little. Forest pathologist Mike McWilliams guided Atlas Obscura around the location and indicated what to observe. He removes the bark from an infected fir with a Pulaski, revealing cream-colored fans of fungal tissue flattened against the wood. Below the surface, it extends as rhizomorphs, black strands resembling bootlaces, connecting one root system to another. In the fall, it occasionally produces fruit, resulting in clusters of honey mushrooms at the base of sickly trees. They are safe to eat, although the Oregon Encyclopedia warns they can upset some stomachs and should be thoroughly cooked.