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Some mushrooms are extremely poisonous. Why?
Don't ask AI if you're wondering whether a mushroom is poisonous, a mushroom expert warns. She has better advice.
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Eating the wrong mushroom can lead to liver damage, kidney failure, and death within a relatively short time if you do not receive prompt treatment.
But why have a few mushrooms evolved to produce something that is so extremely toxic to us? And why are only a few of them so dangerous?
Are these mushrooms trying to protect themselves from humans and other creatures that might eat them?
The mushroom’s body
“It’s often said that toxins in nature serve as a defence against being eaten, acting as antifeedants,” Solveig Bua Løken tells Science Norway.
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She specialises in fungi and works as a collection manager in the fungal collections at the University of Oslo’s Natural History Museum.
But she does not believe this is the case with poisonous mushrooms. She thinks it may be more coincidental that a few mushrooms are extremely toxic to humans and certain other mammals.
The death cap (Amanita phalloides), which is one of the most dangerous mushrooms for humans, can kill both dogs and cats, according to the Norwegian Veterinary Institute.
“But these substances are not universally toxic,” says Løken. “There are many other organisms that can eat them, such as insects and other fungi.”
She points out that what we actually pick is the part of the mushroom that protrudes above the ground, known as the fruiting body. This is the mushroom’s reproductive organ.
No need to protect itself
The mushroom’s body is underground, and is called the mycelium.
When the fungus is ready to reproduce, the fruiting body comes out to spread spores.
“It is very short-lived. It doesn’t take long for a fruiting body like this to grow and disperse its spores,” says Løken.
It then rots relatively quickly. Since this is such a short-lived stage, perhaps it does not matter very much what happens to the fruiting body after the spores have been dispersed.
"I don't think there is strong selection pressure for it to avoid being eaten," the researcher says.
In other words, the mushroom does not need to develop toxins in order to survive. So what is the reason?
Dangerous substances
In these mushrooms, there are primarily two groups of substances that are extremely dangerous to us: amatoxins and orellanine.
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Amatoxins are found in death caps (Amanita phalloides) and destroying angels (Amanita virosa). These substances are scary because they act slowly.
Around eight hours after you have ingested them, you can become ill. You can also develop painful diarrhoea. Your liver and kidneys can be damaged, and if left untreated, poisoning is often fatal, according to the encyclopedia Britannica.
Orellanine is found in deadly webcaps (Cortinarius rubellus) and fool’s webcaps (Cortinarius orellanus). It may take several days before symptoms start. The substance can cause kidney failure and can therefore be fatal.
The toxicity of webcaps may be linked to the mushrooms' absorption of heavy metals, a hypothesis you can read more about in the research magazine Apollon (link in Norwegian).
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Toxins may have unknown functions
Solveig Bua Løken points out that there are examples of toxins that are extremely beneficial to the fungi that produce them, such as penicillin. This is a toxin that kills bacteria and that we use as an antibiotic.
But it is uncertain whether these dangerous toxins have any special value for the mushroom species that produce them, Løken tells Science Norway.
“It may well be that these substances have functions in the mushroom that we are not aware of, and that their toxicity for us is merely a by-product,” she says.
It could also be an example of a substance that simply persists through the evolutionary process without being particularly useful or harmful to the fungus. It is simply not useless enough to disappear.
AI has little to contribute
In any case, you need to be careful around these mushrooms, especially if you plan to eat them.
And don’t ask AI, the mushroom expert says. It’s too dangerous.
“No, AI has little to contribute here,” she says.
She points out that you can use a digital mushroom identification service or visit an in-person mushroom inspection station. There, experts examine the mushrooms you’ve picked to ensure no poisonous ones have made it into your basket.
“If you’re planning to eat them, I would always go to a mushroom inspection station,” she says.
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Translated by Nancy Bazilchuk
Read the Norwegian version of this article on forskning.no
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