An Underground Vastness
What would you think if I told you that in a United States national forest exists an organism so large that it spans an area equivalent to over 1600 football fields, lives 3 feet underground, and is fatal to many trees that come into contact with it? Although it sounds like something straight out of a horror movie, this organism is real, alive and growing in the state of Oregon. But before I go into more details about it, I want to define what is meant by "largest organism".
When you look upon a tree growing in your yard, you see the trunk, branches, twigs and leaves, and generally those parts, together, constitute the organism. However, this tree has an extensive root system as well. These roots are connected to the above-ground parts, making the tree of considerably larger size. So long as all the cells of all the parts are genetically identical, and are all connected as one, the entire entity is one organism. That understanding will help you to grasp how what may seem like a small group of mushrooms actually represents part of the largest living organism on Earth.
What you see is much larger than it appears!
In the Malheur National Forest of eastern Oregon, a really gigantic specimen of Armillaria ostoyae, or the Honey Mushroom, is growing. The fruiting bodies of this vast organism are seen as clusters of mushrooms (see thumbnail picture above, right), but the continuous underground part of the fungus extends over 3.5 miles and an area of around 2200 acres. Such size is not attained without age, and this organism has been dated variously from 2400 years old to over 7000 years old. The presence of this large organism is not a friendly event for many evergreen trees in the area, as this fungus is also known as root rot. Quite a few trees have succumbed to the ravages of this relentless creature. Periodic forest fires keep it at bay, but the dry climate discourages the growth of competing fungal colonies..
In addition to the weblike fungal hyphae or mycelia that penetrate the trees, this fungus produces stringy rootlike structures called rhizomorphs that grow and seek out new trees to infect. Even though the growth of this organism is the death knell for the susceptible evergreen trees it encounters, the fungus plays a vital role in the evolution of the ecosystem within which it grows.
In Fall, the mushrooms emerge and their emergence is the only evidence of the existence of this organism, save for the dead and dying trees left in its wake. The mushrooms are reputed to be edible, and by some accounts tasty, but I have no firsthand experiences in eating them.
It's in the genes!
Scientists studying this humongous fungal specimen were able to determine that it is one vast organism by doing detailed DNA analyses of samples from widely separated locations. The samples proved to have the same genetic constitution, even when separated by acres. Thus the results of the study confirmed that this specimen of Armillaria was indeed a single connected specimen rather than separate organisms of the same species.
Image credit: Wikimedia Commons