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Why are some mushrooms poisonous?

When foraging for mushrooms you are always advised to make sure you have an expert with you to properly identify poisonous and non-poisonous mushrooms. But why are some mushrooms poisonous and others not? The simple explanation is that evolution has taught some mushrooms to produce a toxin to avoid being consumed by other species so they can properly reproduce. Other mushrooms want to be eaten to spread their spores through poop and insect/animal dispersal. The tricky part in this is that poisonous mushrooms are not more colorful or distinct in any specific way to their non-poisonous counter parts. In our world, we know the more colorful the snake or frog the more deadly or poisonous it usually is. The differences in mushrooms are so slight even an experienced mycologist can make a mistake. Here are some facts about these poisonous mushrooms:

-The toxins in mushrooms may be harmless to other organisms like snails, insects, or animals. This does not mean they are safe for humans to eat.

-All mushrooms may darken or bruise when touched or damaged.

-There is no obvious taste difference between poisonous and non-poisonous.

-Cooking, canning, freezing or drying will not make a mushroom non-poisonous.

-Symptoms of poisoning can be delayed hours, even days.

Three of the most deadly mushrooms are the Death Cap, Funeral Bell, and Deadly Dapperling. Great names am I right! All three of these mushrooms produce the toxin called amanitin. Scientists believe this toxin was present in a fungus form in forest soils and present in ancestors of these specific mushrooms. The genes to produce this toxin were passed on through a horizontal gene transfer, which is the transfer of genetic information between organisms, which includes the spread of antibiotic resistance genes among bacteria. This actually happens with humans, when we have bacteria that is resistant to antibiotics. There have been four genes identified in the production of amanitin. The presence of these genes tells us one thing, but when there are identified copies of the genes, this means more toxin is produced and a higher accumulation of it in the mushroom. There are around 7,000 poisonous mushroom ingestions per year, so make sure you have an expert with you before you pick and eat. When in doubt, don't bother.

There are many online resources for mushroom identification. Most of these will ask you to provide a picture of the top and bottom sides of the cap, the whole mushroom, and a picture of the spore print. The color of the spore print can be very important in identifying what type of mushroom you have found. Check out my blog on properly making a spore print for more info. They will also ask to report the environment and geological location it was found.

This blog is for educational purposes. Never consume a mushroom without having it properly identified by a certified expert.

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