The blue whale gets a lot of ink for the being the largest animal to ever live, beating out even the biggest dinosaurs. But it turns out the largest organisms on Earth aren’t in the oceans, they are beneath our feet. By weight and area, honey mushrooms in the genus Armillaria beat whales many times over. Now, reports Matthew Taub at Atlas Obscura, a new analysis of the original “humongous fungus” in Michigan’s Upper Peninsula shows the massive mushroom is much bigger and much older than researchers first believed.
About 25 years ago, researchers discovered that an Armillaria gallica mushroom near Crystal Falls, Michigan, covered about 91 acres, weighed 110 tons and was about 1,500 years old, setting a new record for the largest organism at the time. For a new study published on the preprint service bioRxiv, James Anderson, a biologist at the University of Toronto and one of the original discoverers of the fungus, returned to the site and took 245 samples from the mushroom and examined its genome. The team confirmed that indeed, the entire fungus is just one individual.
The DNA also showed a very slow mutation rate, meaning that the honey mushroom isn’t evolving very quickly. The visit also led them to revise the fungus’s age to 2,500 years and determine that it is four times as massive as the original estimate, or about 440 tons, the equivalent of three blue whales.
How can a mushroom be that big? What we think of as mushrooms are just the fruiting bodies of the organisms. The main part of a mushroom is mass of underground tendrils called mycelium. Depending on the species, these tendrils can feed on soil, decaying plant matter or wood. In the case of the massive honey mushrooms, they have particularly thick black tendrils called rhizomorphs, reports Sarah Zhang at The Atlantic. The rhizomorphs can spread to acre upon acre in search of wood to consume. While other mushrooms prefer already decaying wood, the honey mushroom infects living trees, often killing them over the course of several decades, then continues eating them after they are dead. While it’s possible to find the underground mass by the honey mushrooms that it occasionally sends up, the telltale sign that the fungus is underfoot is the grove of dying trees above it.
The Crystal Falls humongous fungus was the original humongous fungus that showed these organisms can reach massive size. But since its discovery it has been eclipsed by other honey mushrooms. An Armillaria found in eastern Oregon’s Blue Mountains covers three square miles and may be over 8,000 years old, holding the current title for humongous-est of the funguses.
The size and huge distribution of these mushrooms underground is difficult to imagine. “I wish all of the substrate [soil, wood and other matter the fungus grows on] would be transparent for five minutes, so I could see where it is and what it’s doing,” Anderson tells Zhang. “We would learn so much from a five-minute glimpse.”