Fact check: Fake photos of 'humongous fungus,' world's largest living organism, are circulating online

Bayliss Wagner, USA TODAY
·5 min read

The claim: Photos show world’s largest and oldest organism, the Armillaria ostoyae fungus

Here’s a fun fact: The world’s largest organism isn’t a well-fed elephant or a blue whale or even a giant sequoia. It’s a fungus.

If you Google "Armillaria ostoyae" or the fungus' common name, "honey mushroom," the first image you might see shows a mushroom the size of a house, dwarfing a crowd of awestruck hikers. Another photo supposedly of the fungus shows a mushroom with a cone-shaped cap and a stalk as thick as a tree trunk.

These images have attracted numerous visitors to Oregon’s Malheur National Forest, the home of the “humongous fungus,” park officials say. But seekers of a giant mushroom never find what they’re looking for – because the photos are fake.

A Facebook post from July 20 about the Armillaria is one of the latest places where the fake photos have popped up. Malheur National Forest debunked one of the giant-mushroom photos on their Twitter account, while the creators of another photo verified that it was made using photo editing software.

According to forest pathologists for the National Park Service, the real Armillaria ostoyae is not a mushroom but rather a network of fungal threads and cords called hyphae that are almost entirely hidden from sight. A parasitic fungus, it infiltrates tree bark and root systems and spreads out across the forest floor in search of new hosts to colonize.

Unless you’re lucky enough to visit the park during a few rainy weeks in early autumn when small honey mushrooms sprout, the most visible clue of the fungus is on the underside of fallen trees. There, you can see the presence of black, shoelace-like structures entangled with the trees’ root systems.

USA TODAY reached out to the creator of the post for comment.

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What is the 'humongous fungus?'

To understand what the "humongous fungus" is and how it grew so large, it's essential to understand that there is much more to a mushroom than what we can see or eat. All mushrooms are the fruiting bodies of underground fungal networks called mycelia.

A mycelium provides nourishment to mushrooms by creating a mat around organic material, such as the roots of a dead tree, and releasing digestive enzymes.

Unlike many beneficial mushrooms, Armillaria ostoyae is a destructive force in forests, Scientific American writes. Armillaria is able to grow so large because it deploys rhizomorphs – flat, black, shoestring-like cords – in soil, bridging up to a sixty-foot gap between one food source and another. It can infect even live trees, eventually leading to their death.

Armillaria rhizomorphs cover the exposed root system of a tree that was infected with the fungus and toppled by strong winds.
Armillaria rhizomorphs cover the exposed root system of a tree that was infected with the fungus and toppled by strong winds.

Rhizomorphs are what facilitate the incredible growth of the largest Armillaria ostoyae individual in Malheur National Forest. A USDA study estimated in 2008 that it had grown to cover over 3.7 square miles, expanding between 0.7 and 3.3 feet per year. They used those numbers to estimate that the fungus is at least 1,900 years old and could be as much as 8,650 years old. For reference, the neolithic era ended 5,000 years ago.

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Giant mushroom images created by Photoshop

Both photos that bloggers and social media users have used to illustrate the Armillaria are digital creations.

Malheur National Forest tweeted the photo used in the recent Facebook post about the Armillaria to clarify that it is not accurate.

"Every few months a new crazy giant mushroom image shows up on social media referring to the Humongous Fungus," the tweet stated. "While it is true the fungus is the largest living organism, it looks nothing like this."

The photo also shows evidence of digital manipulation. The base of the mushroom seems to float above the grass, and its edges give the appearance of having been altered. Tom D. Bruns, professor emeritus of fungal biology at the University of California-Berkeley, said he couldn’t identify its species but said, “Mushrooms do not get that large.”

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Another photo misattributed to the honey mushroom was made as a joke by fungus researchers

Another photo that has been associated with the Armillaria shows a crowd staring up at a brown-capped mushroom. But that's a “boletus photoshopus,” not a honey mushroom, Bruns told Snopes.

The photo was created by Dirk Redecker, a University of Bourgogne microbiologist who worked in Bruns’ lab. He said the photo came out of a field trip of West Coast mycologists in 2000. The jokey photo features researchers from Bruns' lab and their families.

“We made it for fun,” Bruns told USA TODAY in an email.

Redecker uses the photo to ironically highlight the overlooked fungal networks that nourish the mushrooms we see aboveground.

Our rating: Altered

Based on our research, we rate as ALTERED the two photos claiming to show the world’s largest and oldest organism, the Armillaria ostoyae fungus. The photos are digitally manipulated and misrepresent the structure of the fungus, which is primarily an underground network of fungal threads – not a giant mushroom.

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This article originally appeared on USA TODAY: Fact check: Claim about world's largest fungus uses altered images