Poisonous Mushrooms

Not all mushrooms are appropriate for human consumption, although there is no broad group of poisonous fungi, as many different families contain toxins. Although some toxic species do not kill humans outright and might only cause gastrointestinal (GI) distress such as nausea and vomiting, others can be debilitating and even fatal. They include species that affect the central nervous system (CNS) and induce mild hallucinations, while a small number of taxa contain various toxins that are fatal to humans. There are many types of mushrooms in Arkansas, and the Arkansas Mycological Society (AMS) helps educate its members in the morphological similarities and differences between the harmless and the poisonous.

The number of poisonous (fatal) mushrooms is relatively small, perhaps just over seventy-five species. However, the most poisonous species are common. The only safe and intelligent way for people who wish to consume wild mushrooms is to learn to recognize the botanical fungal characteristics of which ones are truly edible and those that are either questionable or are poisonous. Some local mushroom clubs certify individuals who can then legally sell wild harvested mushrooms to restaurant chefs and at farmer’s markets. While many mushrooms can be accurately identified using only their macroscopic properties, others can only be identified from looking at their spores and other structures using a light microscope. In addition, it is highly recommended to take extra care with white mushroom species, as there are fatal lookalikes. In addition, some small brown mushrooms growing on wood are also deadly poisonous (e.g., members of the genus Galerina). However, when in doubt, follow these three precautionary recommendations: (1) do not eat any mushroom that cannot be specifically identified, (2) do not eat raw mushrooms, and/or (3) if you want to be truly safe, leave all wild mushrooms alone.

Specific toxins from mushrooms are usually categorized by the region of the human body they affect and how quickly those effects are manifested. The species causing the most serious pathologies are those that act as cellular poisons. The amatoxins and phallotoxins (collectively known as the Amanita toxins) are bicyclic octa‐ and heptapeptides, respectively. In addition, monomethylhydrazine (MMH) acting toxins rupture plasma membranes. Within five to seven hours of ingestion, some of the initial symptoms of poisoning include abdominal pain, vomiting, dehydration, diarrhea, hypotension, jaundice, tachycardia, and abnormal body temperature. Unfortunately, these early symptoms of cellular poisoning by mushrooms do not appear until after a long latency (period of remission), which can be from six to seventy-two hours after ingestion. The symptoms of kidney and liver damage soon appear, and severe pain could last as long as three to six additional days when kidney failure leads to death. For some patients, if death does not occur, the illness continues for several weeks and may or may not do permanent damage to the liver.

The agarics of the family Amanitaceae include estimates of about 1,087 species worldwide. Both edible and very poisonous species are included in the genus. There are more species of Amanita in North America whose toxins are inadequately known. This genus is responsible for about ninety-five percent of human fatalities resulting from mushroom poisoning, with the “death cap” accounting for approximately fifty percent on its own. It is therefore recommended that people not eat any species of Amanita.

One of the deadliest of mushrooms is the all-white “green” death cap (Amanita phalloides), which is found throughout Europe (and introduced into North America). It is known in states on both the East and West coasts and appears to be expanding its range into the states in the middle of North America. A. phalloides closely resembles edible paddy straw mushrooms (Volvariella volvacea) and pale forms of Amanita calyptroderma, which is known to be an edible Amanita on the West Coast. Its amatoxins, phallotoxins, and virotoxins are heat stable, can withstand cooking temperatures, and can quickly damage cells throughout the body. Within six to twelve hours after ingestion, physiological symptoms such as violent abdominal pain, vomiting, and bloody diarrhea appear, causing rapid fluid loss from the tissues and extreme thirst (polydipsia). Signs of more serious involvement of the major organs, including the liver and kidneys, along with the CNS soon follow (delirium and convulsions), with a decrease in urinary output (oliguria) and a lowering of blood glucose (hypoglycemia). In more than half of cases, this condition leads to coma and death.

A group of mushrooms called “destroying angels” are famous for being incredibly toxic. They are also very similar in appearance to edible button mushrooms and meadow mushrooms and have been collected and eaten by mistake. One particular species is the eastern North American destroying angel, Amanita bisporigera, considered by some to be the most toxic North American mushroom, often containing enough amatoxins (including α-amanitin and phallotoxins) to kill an adult human. In addition, the destroying angels also include several other species of all-white mushrooms such as the European fool’s mushroom (A. verna) and death angel (A. virosa). Symptoms of poisoning by this species are similar to other Amanita spp.

Several species within the genera Clitocybe, Conocybe, Cortinarius, Galerina, Gyromitra, Inocybe, and Lepiota (especially L. brunneoinccarnata, L. brunneolilaceae, L. castanea, L. josserandii, and L. helveola) cause severe poisoning and even fatal consequences. There are two species of webcap, the deadly webcap (Cortinarius rubellus) and the fool’s webcap (C. orellanus), and they are very similar in appearance to one another and also to several edible varieties. These mushrooms contain a Type 7 toxin known as orellanine, which initially causes symptoms similar to the common flu, including nausea, vomiting, chills, shivering, sweating, and extreme thirst. However, orellanine has an extremely long latency period and can take from two days to up to three weeks to cause symptoms, often leading to a misdiagnosis. The toxin ultimately causes renal failure and death if left untreated. The only orellanine poisoning in North America was in 2008 and involved a Michigan woman in kidney failure who had consumed a Cortinarius species similar to C. orellanus, which is found under oaks. In 2010, this species was described as new, C. orellanosus.

Another poisonous mushroom that is common throughout the Northern Hemisphere (Europe, North America, and Asia) and parts of Australia is the autumn skullcap, Galerina marginata. It is a gilled, wood-rotting, small to medium brown mushroom with the same amatoxins and phallotoxins (Type 1 toxins) as the death cap mushroom. Several deaths and poisonings have been attributed to collectors confusing the autumn skullcap with the honey mushroom (Armillaria mellea) or the hallucinogenic “magic mushroom” or bluestain smoothcap, Psilocybe cubensis. The former contains Type 1 toxins and the latter Type 4 toxins, psilocybin and psilocin. Type 4 toxins affect the CNS and result in moderate to strong hallucinogenic reactions such as sensory and visual distortions, brilliant colors, and problems with concentration. Unpleasant experiences include depression, anxiety, or fear. Gastrointestinal symptoms usually occur after ingesting psilocybin mushrooms (P. cubensis, P. cyanescens, P. pelliculosa, and P. stuntzi) within fifteen minutes to one hour after ingestion. Other mushrooms containing Type 4 toxins include Conocybe cyanopus and Gymnopilus aeruginosa.

The term “false morel” includes a number of different species, including the beefsteak mushroom (Gyromitra esculenta) and Carolina false morel (G. caroliniana), and covers several different species that are often mistaken for the edible delicacies as true morels (Morchella spp.). Many false morels contain Type 5 MMH and gyromitrin toxins that cause nausea, bloat, dizziness, muscle cramps, vomiting, severe headaches, and general pain, which sometimes can lead to death. It is recommended to avoid the false morels altogether as it is not worth the risk. Apparently, however, people in some parts of the world boil and eat them with no apparent ill effect.

A mushroom famous because it is often mistaken for certain types of highly prized gourmet chanterelles is the jack o’lantern fungus (Omphalotus illudens), which can be found in Arkansas during the fall months and other states in central and eastern North America, where it grows on oaks; its congener in Europe is O. olearius. They include Type 8 toxins (atromentin and illudin M and S). They cause nausea, diarrhea, vomiting, and severe cramps. They are not deadly, but poisoning will result in an extremely unpleasant experience. Hospitalization is sometimes necessary, especially if young children ingest the same amounts as adults. What is sometimes referred to as green-spored Lepiota (Chlorophyllum molybdites) is very common in Arkansas and many other states during the summer months. It can cause sickness from Type 8 toxins, including gastric upset, vomiting, and diarrhea but not deadly results. Other mushrooms that are capable of causing gastroenteritis include some species of pinkgills (Entoloma), dark disks and poison pies (Hebeloma), milkcaps (Lactarius), and sickeners and brittlegills (Russula). Symptoms include intestinal cramps, diarrhea, and vomiting,

Members of the genus Agaricus can be quite common on lawns as well as in the woods. There are some edible species as well as some that can cause GI upset. Edible species that are known to occur in Arkansas include: Agaricus auricolor, A. abruptibulbus, A. porphyrocephalus, A. andrewii (commonly called A. campestris) and A. arvensis. Three poisonous Agaricus species that can be found in Arkansas include A. pocillator, and A. placomyces.

There is no comprehensive list of poisonous species of mushrooms that occur in Arkansas. However, the very toxic A. bisporigena (as well as A. suballiacea) and some other poisonous Amanita spp., for example, A. atkinsoniana, A. polypyramis, and A. ravenelii, are common in the state, especially during summer months. They are often found in woodlands in the vicinity of oak (Quercus) and pine (Pinus) trees, including urban yards. Because they are found in yards, pets and sometimes young children eat them and can get very sick or even die.

In Arkansas, the Arkansas Mycological Society (AMS) educates its members in the morphological similarities and differences of various types of mushrooms, particularly poisonous ones. A national society, the North American Mycological Association (NAMA), promotes, pursues, and advances the science of mycology. In Arkansas, the Poison Center at the University of Arkansas for Medical Sciences or a physician should be contacted for help in case of ingestion of a poisonous mushroom. Most centers maintain active call lists of mycologists who are knowledgeable concerning local prevalence of mushroom genera and species and can assist in mushroom identification. The individual should be immediately taken to the emergency room, along with a sample of the mushrooms the person ingested, if possible. For most patients with mushroom poisoning, supportive care and GI decontamination with activated charcoal suffice for proper management. However, more intensive care such as kidney dialysis and potentially liver transplant might be necessary to recover from permanent damage in extreme cases.

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Chris T. McAllister
Eastern Oklahoma State College