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xtruss · 8 months

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Environment: Death Cap Mushrooms are Extremely Deadly—and They’re Spreading

The Invasive Death Cap Mushroom is thriving in North America. While it can be difficult to distinguish from an edible one, make no mistake: It can do a number on you.

— By Emily Martin | August 31, 2023

The Death Cap is the World's Deadliest Fungus, responsible for 90 percent of the World's Mushroom-related Poisonings every year. Native to Europe, Death Caps have spread around the World over the past Century. Photograph By Yves Lanceau/Nature Picture Library

The name itself is both alarming and self-explanatory: the death cap mushroom.

Scientifically known as Amanita phalloides, death caps are responsible for 90 percent of the mushroom-related fatalities that occur every year, making them the world’s most lethal mushroom. The infamous fungus was recently in the news after three people in Australia died after ingesting what investigators suspect were death caps.

The mushroom originates from the U.K. and parts of Ireland, but over the past century, it has hijacked trips around the world, spreading to Australia and North America.

Since arriving on the West Coast, the invasive mushroom has spread rapidly throughout California and has even appeared as far north as British Columbia, but much about its arrival remains a mystery. Why the mushroom spread so quickly, when exactly it arrived, and how it will impact the environment it grows in are the topics of ongoing research.

Here’s what you need to know about this deadly mushroom—and how to spot one—in case it emerges in a forest near you.

How The Mushroom Earned Its Name

The unassuming mushroom can grow up to six inches tall with a similarly sized domed cap, sometimes tinged yellow or green. Under its cap are white gills and an off-white stem—characteristics that make it difficult to distinguish from an edible mushroom.

Yet unlike an edible mushroom, it can cause extreme damage to the liver and kidneys, or in some cases, death.

That’s because the mushrooms contain a unique set of toxins, says U.S. Department of Agriculture plant pathologist Milton Drott. Though it is safe to the touch, a death cap contains amatoxins, which prevent cells from creating proteins, ultimately causing cell death and organ failure.

Drott notes that these toxins may have allowed the populations spreading through the U.S. to thrive, serving up a defense against any new predators the fungus encounters in its environment.

But studying the death cap mushroom can be difficult. It’s challenging to replicate ideal environmental conditions for a mushroom in a lab, and studying plucked mushrooms requires complex DNA sequencing.

Some fungi can damage the environment, like the fungus that wiped out American Chestnut trees, but so far, there’s no strong evidence that death caps are a threat to their new environments. In fact, trees and other plants benefit from their presence.

Death caps are a mycorrhizal fungi, which means they form a relationship with plants that’s mutually beneficial for both plant and fungus. The plant receives nutrients from the soil that the fungus extracts, while the fungus receives sugars from the plant.

A Mysterious Move Around The World

It’s nearly impossible to pinpoint the actual moment the deadly mushroom made its way to the western U.S. and why exactly it’s continued to spread since then, says Anne Pringle, a mycologist at the University of Wisconsin-Madison and a leading expert on death caps.

The earliest record of the mushroom in California is from the 1930s. Some researchers theorize that death caps immigrated in the soil of a cork tree transported from Europe to California to make corks for a then burgeoning wine industry. Others say the mushroom may have hitched a ride on a mystery plant imported to beautify college campuses.

Regardless, both Pringle and Drott say the only thing they’re certain of is that the fungus was likely dormant—and thus hidden from human eyes—in an imported plant’s soil.

Scientifically known as Amanita Phalliodes—Death Caps were first spotted in California in the 1930s. Some scientists think they were imported in the soil of cork trees, used to make corks for California's wine makers.

“When they planted that tree in the ground, they also effectively planted the fungus. So, what exactly is the smoking gun, who did it, and when—that's the thing I think we'll never truly know,” Pringle says.

Pringle can’t say for sure what makes the state such a friendly habitat for the invasive species, but she does note that the fungus can tolerate different environments throughout Europe, growing as far north as Sweden and as far south as southern France.

Since arriving, Pringle says its geographic extent has grown larger and spread to other States; most recently it appeared in Idaho.

Retracing Their Steps

When scientists first spotted death caps in the U.S., they thought they may be native to the region because of how widespread they are.

In 2009, Pringle was the first to label the population in California as invasive, a discovery she made by inspecting the mushrooms’ DNA.

“When they planted that tree in the ground, they also effectively planted the fungus. So what exactly is the smoking gun, who did it and when, that's the thing I think we'll never truly know.”

— Anne Pringle

And when scientists did realize the death cap had newly spread into the U.S., there wasn’t any preexisting data to provide clues about where exactly it entered North America and how quickly it multiplied.

“There's so many ideas to test, it’s hard to even know where to get started,” Pringle says.

Research on invasive fungi in the environment is quite new, Pringle says, so answers to questions of why death caps are spreading and its impact on local ecosystems may still be years away.

Drott thinks the mushroom may be proliferating because it thrives in its new soil and with its adoptive plants, or there may be a lack of predators in these new habitats to keep death cap populations in check.

His research has revealed at least one clue: the genes responsible for producing toxins in American death caps are extremely unique, distinct from their genetic cousins in Europe, and may be the key to understanding how the invasive plant has thrived in North America.

Earlier this year, scientists published preliminary research suggesting the death cap can reproduce both with and without a mate, and that a single fungus can live a long, reproductive life.

Encountering A Death Cap

Spotting a death cap requires vigilance.

“It’s scary that these [pass for] delicious mushrooms,” Drott says.

He adds that, in addition to an unalarming physical appearance, the death caps’ toxins don’t smell or provide any other obvious giveaways. Its toxins are also extremely stable when heated and don’t break down when cooked, unlike other edible fungi that are only dangerous to eat raw.

That’s why scientists suggest erring on the side of caution and steering clear of foraging mushrooms. Pringle also emphasizes the importance of learning the plants in your local environment.

“If you can tell the difference between Swiss chard and spinach, you can learn difference between edible and poisonous mushrooms,” Pringle says, emphasizing the small but recognizable differences between the two greens. “People want a magic rule, but there’s nothing I can hand you in a sentence or paragraph."

Rather, she says identifying physical differences between death caps and a safe mushroom can become easier with exposure.

Spreading Awareness

Many death caps have been found in National Parks, including Point Reyes National Seashore in California, where Pringle assisted with a study on the invasion in 2010.

National Park Service (NPS) science advisor Ben Becker notes that parks are constantly seeing new invasive species with the frequent movement of people and equipment, and the death cap is a good example of how humans can transport tiny fungal invaders around the world.

Becker says NPS works with local mushroom science groups like the Bay Area Mycological Society to spread public awareness about the dangers of foraging mushrooms.

If you’re concerned about something you have eaten, go to the emergency room and if possible, take pieces of the mushroom you ate for identification.

And as many foragers and scientists say, don’t munch on a hunch.

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xtruss · 2 years

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The mushrooms we pluck from the ground are just the tips of large fungal networks that live underground and in trees. Photograph By Rebecca Hale, National Geographic Image Collection

Fungi Are Key To Our Survival. Are We Doing Enough To Protect Them?

For almost a decade, one lone mushroom was classified as an endangered species, and scientists say more could be in trouble.

— By Sarah Gibbens | Published March 18, 2021 | Environment | Planet Possible

When Italian botanist Giuseppe Inzenga first tasted the white ferula mushroom in 1863, he described it as one of the tastiest he had ever had.

Once found in just 38 square miles on Sicily’s Madonie mountain range growing in limestone and at elevations of over 1,000 feet, the prized mushroom is sold for around 50 euros for two pounds.

“This mushroom is really delicious. You can eat it raw and also cooked,” says Giuseppe Venturella, a mycologist at the University of Palermo in Sicily. He compares it to a porcini, notes that it’s rich in B vitamins, and says the best way to experience the taste is eating it raw, with a little olive oil and parmesan cheese.

“The taste is mild and very pleasant,” agrees Georgios Zervakis, a mycologist at the Agricultural University of Athens who has been studying the species for three decades.

Pleur nebrodensis, White Ferula Mushroom. Photograph By Giuseppe Venturella

Fast forward 100 years from Inzenga’s enthusing, and the same mushroom species, still prized for its taste, is now listed as critically endangered by the International Union for the Conservation of Nature, an organization that tracks population numbers for many of the world’s species.

Picking the mushroom is off limits in protected areas inside the Madonie National Park region, but foragers can pluck mature mushrooms, indicated by a cap with sides growing longer than three centimeters, in surrounding regions. Unlike most mushroom species, the white ferula fruits in spring, with its season lasting from April to late May.

The white ferula mushroom (Pleurotus nebrodensis) grows in the Madonie Mountains of Sicily at an altitude of 1,200-2,000 meters.

Source: IUCN

The white ferula was the first mushroom to be recognized for the impact humans were having on its survival, and from 2006 to 2015 it was the only one of its kind to be globally recognized as endangered.

“It was so beloved by people in [Sicily] that when the numbers began to decline, it was part of popular conversation,” says Nicholas Money, a mycologist at Miami University in Ohio.

But what about the mushrooms we don’t notice? And how many of them are endangered?

“We think the true biodiversity of fungi is somewhere between one million and six million species,” says Anne Pringle, a University of Wisconsin-Madison mycologist—as fungus experts are called—and a National Geographic explorer. Yet despite their global prevalence, fungi have historically been left out of conservation initiatives.

“Because people eat it,” says Pringle of the white ferula, “they notice and care. There might be more than a thousand stories like that of fungi in trouble that we just don’t know about.”

So how do we conserve organisms we can’t see and don’t understand? And why should we try?

“Life on the planet wouldn’t exist without fungi as we know it,” says Greg Mueller, a mushroom conservation expert and the chief scientist at the Chicago Botanic Garden.

Conserving them, Money says, “is an urgent concern because of their relationship with forests and trees. You can’t have the trees without the fungi…. We cannot survive without them. In terms of the health of the planet, they’re incredibly important.”

Fungi, Mushroom, Mycelium—Oh My

Mushrooms as we know them—the cute buttons and flat caps that pop out of soil—are only a small, reproductive part of a larger fungal organism. The above-ground portion is referred to as the fruit body, but below ground, it’s connected to a large network of thin, microscopic threads called mycelium. In 1998, scientists determined that the largest organism on Earth, at least by area covered, was a fungus in Oregon’s Blue Mountains whose mycelium spanned over 2,000 acres underground.

Some so-called mycorrhizal fungi form symbiotic relationships with plants. As many as 90 percent of the common plants we see on land have a beneficial relationship with fungi.

“The fungal filaments penetrate the roots of the plant, forming a placenta-like connection between the fungal colony and the roots,” says Money. “It’s like an additional root system for the plant.”

These root networks help plants take in additional water, minerals, and nutrients, and in return the fungus gets a portion of the sugars plants generate from photosynthesis.

Scoop a chunk of dirt out of soil, and you’re holding unseen mycelium, says Pringle. Advances in DNA sequencing have helped scientists see that fungal DNA sequences live unseen in everything from dirt to the nectar of a flower.

This, however, also makes them hard to count. Depending on the species, mycelium might sprout anywhere from one to several fruiting bodies, meaning what we see above ground doesn’t correspond to how many individuals are living below.

“There might be a mycelium under the ground that sends up one mushroom here and one mushroom here,” says Pringle. “Are they two individuals? Or are they coming from the same individual underground?”

“There are ways to solve it,” she notes, “But they’re time intensive and expensive.” Her work has focused on genetically sequencing fungi to help distinguish them.

State of the Fungi

In a 2018 report assessing the state of the world’s fungi, scientists found that compared to the 68,000 animals and 25,000 plants that had been evaluated to assess whether they were existentially threatened, only 56 fungi had been evaluated. Currently, 168 mushrooms have been assessed as threatened around the world.

Tibetan nomads inspect cordycep fungi for sale at a market. The fungus is known for its medicinal value and fetches a high price as a result. Environmentalists warn that over harvesting the species could harm local mountain grasslands. Photograph By Kevin Frayer, Getty Images

Overharvesting mushrooms, like the white ferula in Sicily, contributes to their decline. In addition to being eaten, many mushrooms are also prized for their medicinal value. The caterpillar fungus found in Tibet, cordyceps sinesis, is used to treat everything from coughing to back pain. Chaga mushrooms, found around the world and sold as a cure for seemingly everything, are increasingly being overharvested, threatening populations in certain regions.

Mushrooms also face many of the same threats plants contend with. Habitat loss, pollution, and specifically the use of fungicide-laden fertilizer, wipe out mushrooms. Studies show that climate change also affects mushrooms, changing the temperature and humidity levels that determine when they pop a fruiting body out of the ground.

Scientists are currently working to understand the effect fungi themselves might have on the climate.

In 2013, Mueller and his colleagues launched the Fungal Red List as a subsection of the International Union for the Conservation of Nature. The initiative was launched when just three fungi—two lichens and the white ferula—were listed as endangered, and it sought to highlight the importance of conserving fungi.

“Another great advance that’s helped is the engagement of the citizen science community,” says Mueller. Mushroom-hunting clubs and websites like iNaturalist and Mushroom Observer allow amateur mushroom enthusiasts to log the mushrooms they find and thus generate more field data for scientists.

Pringle, who serves as the vice president of Mushroom Observer, notes that the site has even helped rediscover species previously thought to be extinct, like a fungus called hazel fingers found in the Appalachian mountains and parts of the U.K.

In the past decade, the white ferula has been found in other parts of Sicily and Greece, meaning the species should be downgraded from critically endangered to endangered, says Zervakis.

Fantastic fungi: Mushrooms spout in nature’s damp corners, a National Geographic report (and Casual Foragers) find. The image of these orange fungi sprouting in a cloud forest in Ecuador got more than 300,000 likes on our Instagram page. Many researchers believe mushrooms are the key to life, but we may not be doing enough to protect them. Photograph Javier Aznar

Why Does it Matter?

Not only are fungi crucial partners for trees, as Money says, they affect the climate of the whole planet.

Walk through a temperate forest in autumn and everything you see on the ground—leaves, branches—is dead. But beneath that layer of dead material is a thriving world of fungi working to decompose it. Studies show that fungi help break down the carbon stored in plant material, locking it into soil. Around the world, soil is a massive reservoir for carbon pollution, holding more carbon than the atmosphere and plants combined.

We’re still learning exactly how fungi play a role in the carbon cycle, which ones are crucial, and how many we need, says Pringle.

“Say there are 100 species [of fungi] that cycle carbon through a forest,” says Pringle. “Can we lose one of them? Ten of them? Fifty? Sixty? Maybe we can lose 99 of them. How many species can we afford to lose before we reach a tipping point, and we’re in some sort of trouble?”

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