Tom Volk's Fungus of the Month for May 2002

This month's fungus is Gyromitra esculenta, one of the false morels.

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Gyromitra esculenta

Gyromitra esculenta is one of several common species of false morels found in the spring about the same time as the true morels. It is also sometimes known as the beefsteak morel, or the lorchel. The Gyromitra species are Ascomycota that superficially resemble the Morels (Morchella esculenta, M. elata and related species). They can be found in roughly the same areas as the true morels and the two genera often grow in close proximity to one another. In our area we usually find false morels rather close to fallen logs, where a microniche of moisture, humidity, and shade is likely to be found, but there is quite a bit of variability in their habitat.

True morels are considered to be delicious and one of the most sought after of the edible fungi. False morels should be considered to be poisonous and should probably not be eaten in most parts of the world. I'll tell you more about this below. Fortunately true morels and false morels are relatively easy to distinguish from one another. The easiest way to distinguish them is by making a longitudinal section of the fruiting bodies. As you can see in the collage below and to the right, a Gyromitra fruiting body has a cap that is not attached to the stalk except at the very top, while in most Morchella, the cap is fused to the stalk for its entire length. The first two pictures are G. esculenta and G. caroliniana, and the picture on the right is a Morchella. Also notice that the stalk of the false morels is filled with more stipe material or sometimes a cottony mycelium, while the stipes of morels are always hollow. There are some microscopic differences in the ascospores as well, with Gyromitra spores containing one or more oil droplets when viewed in KOH. Morchella spores lack these oil droplets.

Gyromitra esculenta G. caroliniana  and Morchella longitudinal sections

Despite its specific epithet "esculenta" meaning "delicious," this fungus should not be considered edible. Eight to ten species of Gyromitra exist on the North American continent and about two or three in Europe. Although they are much sought after in Europe as an edible species (Gyromitra esculenta), 2 to 4 per cent of all mushroom fatalities are associated with them. It is not clear whether the same species occurs in North America, although we call one species here by that name. The active ingredient is called gyromitrin (N-methyl-N-formylhydrazine), which is metabolized to monomethylhydrazine (rocket fuel!) in the body. Eaten raw, most of the Gyromitra spp. are quite poisonous. In an attempt to prevent poisoning caused by ingesting the mushrooms, they are usually parboiled to evaporate the gyromitrin, which gives off a chocolaty odor. The process is usually repeated twice, with the water being discarded each time. However, the volatile chemical can be inhaled through the nose, and enough can be left in the mushrooms to cause illness when eaten. So just standing near the boiling pot of mushrooms can cause problems, and there is still the possibility of poisoning by ingestion.

Gyromitrin is a hemolytic toxin (i.e. it destroys red blood cells) in humans, other primates, and dogs. It is toxic to the central nervous system and damages the liver and gastrointestinal tract. It may act by interfering with transaminases, particularly those having a pyridoxal phosphate cofactor. Vitamin B6 is used in the treatment. As in cyclopeptide poisoning, a relatively long latent period ensues (6 to 12 hours) between ingestion and symptoms. The symptoms include nausea, vomiting, diarrhea, cramps, distention, weakness, lassitude, and headache; if the condition is severe, these may develop into jaundice, convulsions, coma, and death. Methemoglobinuria and very low blood sugar are found in laboratory tests.

Toth et al. (Toth, B., K. Patil et al. 1979. False morel mushroom Gyromitra esculenta toxin: N-methyl N-N-formylhydrazine carcinogenesis in mice. Mycopathogia 6:121-128) have found N-methyl-N-formylhydrazine to be carcinogenic. When it was administered to mice at concentrations of 0.0039 per cent (i.e. 39 ppm) in drinking water, tumors were found in lungs, liver, blood vessels, and bile ducts. The tumors included adenomas, adenocarcinomas of lungs, benign hepatomas and liver cell carcinomas, angiomas and angiosarcomas, and other types.

Ken Cochran of the University of Michigan has tested many Gyromitra specimens from many parts of North America for toxins. He showed that gyromitrin is found in most Gyromitra species in significant amounts. Some species (e.g. G. gigas and G. caroliniana) apparently contain little of the toxin, although most wild populations have not been tested. Small amounts have been detected in related ascomycetous fungi and even in Agaricus bisporus (= A. brunnescens ), the white button cultivated mushroom. Carcinogenesis of this compound for humans has not been determined.

So although many people have eaten this mushroom for many years, in my opinion you are playing a game of Russian roulette (no offense intended to any Russians or to any NRA members reading this...) if you decide to eat Gyromitra esculenta or even other Gyromitra species. First of all there is the possibility of getting sick just from inhaling the fumes from the parboiling. There is a second possibility of ingesting incompletely removed toxins when you eat the mushrooms. Third, there is the likelihood that gyromitrin is a cumulative carcinogen, which may cause problems in the short term or only after many year of ingesting or inhaling the toxin. There are many people who tell me they have eaten these false morels for many years without any problem. I reply to them that they have been lucky so far. Certain populations of the mushrooms are known to contain different amount of the toxin, so it's possible they have been eating mushrooms with less toxin. Eating mushrooms from a different "patch" of false morels could give a very different result, depending on their concentration of toxin. The scariest part of this is that we don't know the long-term cumulative effects of ingesting small amounts of the toxin each year. So even though you might find lots of false morels while out morel hunting, and you're very temped to eat them because of their large size and meaty texture, I do not recommend eating false morels. If you must eat them, please do not feed them to children or to pregnant women, who are especially vulnerable to the toxin. You should also avoid eating them on consecutive days to prevent dangerous buildup of the toxin. ONLY *YOU* ARE RESPONSIBLE FOR YOUR EATING HABITS. Do not feed this mushroom to others without fair warning. Better yet, have them read this page.

Gyromitra brunnea with Dan CzederpiltzThere are several other species of Gyromitra in North America. The most common species in our area of Wisconsin and Minnesota is Gyromitra brunnea, shown to the left with my former undergraduate student, Dr. Dan Czederpiltz. The mushrooms can grow to be very large, but I have not even been tempted to eat one. The mushroom to the right is Gyromitra caroliniana, which is sometimes called "Big Red" in Missouri and Arkansas. It can grow to be quite large, as attested by this 3.75-pound (1.7 kg) monster. It apparently contains very little if any gyromitrin, although not all populations have been tested. The range of G. caroliniana overlaps with that of G. brunnea, so in those areas you have to sure of your identification. In our area Gyromitra infula and G. ambigua fruit in the fall and should not be eaten. It generally has a rather smooth cap. Other midwestern/eastern species include G, korfii, G. sphaerospora, and G. fastigiata.

In western North America there are a couple other species of Gyromitra, including the generally-regarded-as-safe Gyromitra gigas. However, G. gigas appears to be a complex of species that differ in their amount of toxin, so care should be taken if you're going to eat these. Current taxonomic methods do not allow for easy differentiation between the several species in this complex. Gyromitra californica, with its reddish-pink overtones, also occurs in the west. It should probably never be eaten. Gyromitra montana also occurs in the west.

Gyromitra caroliniana, 3.75 lb, 1.7 kg

If you're interested in learning more about morels and false morels, I highly recommend that you read Nancy Smith Weber's book, "A morel hunter's companion: A guide to the true and false morels of Michigan." Two Peninsula Press. 1988. ISBN 0-941912-10-8.

I hope you enjoyed learning something about Gyromitra esculenta and its relatives today. Maybe it's the only thing you'll find in the woods when you're out hunting for morels-- and being so big, they *are* lots of fun to find. However, despite the temptation, I do not recommend eating this mushroom. In my opinion, and according to the picture below, Gyromitra is just a toadstool.

Gyromitra brunnea toadstool

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This page and other pages are © Copyright 2002 by Thomas J. Volk, University of Wisconsin-La Crosse.

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