Which Mushrooms Are Poisonous?

There is no easy way to tell. The FDA's Bad Bug Book says that for people who are not trained experts in mushroom identification, there are generally no easily recognizable differences between poisonous and nonpoisonous species, and there is no reliable rule of thumb for distinguishing edible mushrooms from poisonous ones. CDC's MMWR says about 7,500 poisonous mushroom ingestions were reported annually to US poison control centers, and that the public should be aware that poisonous mushrooms might resemble nonpoisonous ones, that cooking does not remove or inactivate the toxins, and that wild mushrooms should never be eaten unless identified by an expert.

Amatoxins are the deadliest group. The Bad Bug Book says amanitin poisoning has a long symptom-free period of 6 to 48 hours, averaging 6 to 15 hours, followed by sudden, severe abdominal pain, persistent vomiting and watery diarrhea, extreme thirst and lack of urine production. CDC's MMWR says amatoxins are not denatured by cooking or other food preparation and cause a delayed onset of symptoms, which can contribute to fatal outcomes.

Other groups act differently. The Bad Bug Book says orellanine, from the Sorrel Webcap mushroom and some of its relatives, causes poisoning with an extremely long symptom-free period of 3 to 14 days, beginning with intense burning thirst and excessive urination, and that in severe cases kidney failure may cause death several weeks later. It says certain false morels contain gyromitrin, whose poisoning superficially resembles Amanita poisoning but is less severe, and that some Inocybe and Clitocybe species contain muscarine, which causes increased salivation, sweating and tearing within 15 to 30 minutes of eating.