| Gyromitra esculenta | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Pezizomycetes |
| Order: | Pezizales |
| Family: | Discinaceae |
| Genus: | Gyromitra |
| Species: | G. esculenta |
| Binomial name | |
| Gyromitra esculenta | |
| Synonyms[1] | |
| |
| Gyromitra esculenta | |
|---|---|
| Mycological characteristics | |
 | Smoothhymenium |
 | Cap is convex |
 | Hymenium attachment is not applicable |
 | Stipe is bare |
 | Spore print is yellow to buff |
  | Ecology issaprotrophic ormycorrhizal |
  | Edibility isedible butnot recommended |
Gyromitra esculenta/ˌdʒaɪroʊˈmaɪtrəˌɛskjəˈlɛntə,ˌdʒɪrə-/[2] is anascomycete fungus from the genusGyromitra. Thefruiting body, or mushroom, is an irregular brain-shapedcap, dark brown in colour, that can reach 10 centimetres (4 inches) high and 15 cm (6 in) wide, perched on a stout whitestipe up to 6 cm (2+1⁄2 in) high. It is widely distributed across Europe and North America, normally fruiting in sandy soils underconiferous trees in spring and early summer.
Although potentially fatal if eaten raw,G. esculenta is sometimesparboiled for consumption, being a popular delicacy in Europe and the upperGreat Lakes region of North America. However, evidence suggests that thorough cooking does not eliminate all toxins. When consumed, the principal active mycotoxin,gyromitrin, ishydrolyzed into the toxic compoundmonomethylhydrazine, whichaffects the liver,central nervous system, and sometimes thekidneys. Symptoms involve vomiting and diarrhea several hours after consumption, followed by dizziness, lethargy and headache. Severe cases may lead todelirium, coma, and death. Recent evidence suggestsG. esculenta may be chronically toxic and linked to regional clusters ofALS.[3]
The fungus was first described in 1800, by mycologistChristian Hendrik Persoon, asHelvella esculenta,[4] and gained its current acceptedbinomial name when the Swedish mycologistElias Magnus Fries placed it in the genusGyromitra in 1849.[5]
It is known by a variety of common descriptive names such as "brain mushroom",[6] "turban fungus",[7]elephant ears,[8] or "beefsteak mushroom/morel", althoughbeefsteak mushroom can also refer to the much choicer edible basidiomyceteFistulina hepatica.[9] Dating from the 19th century, the German termlorchel is a result of the olderlorche, itself from the 18th centuryLow GermanLorken, aligning with the similar-sounding (and similar-looking)morchel.[10][11]
Gyromitra esculenta is a member of a group of fungi known as "false morels", so named for their resemblance to the highly regarded true morels of the genusMorchella. The grouping includes other species of the genusGyromitra, such asG. infula (elfin saddle),G. caroliniana andG. gigas (snow morel). While some of these species contain little to no gyromitrin, many guidebooks recommend treating them all as poisonous, since their similar appearance and significant intraspecific variation can make reliable identification difficult.[12] The toxic qualities ofG. esculenta may be reduced by cooking, but possibly not enough to prevent poisoning from repeated consumption.[13]
The more distantly related ascomycete mushrooms of the genusVerpa, such asV. bohemica andV. conica, are also known as false morels, early morels or thimble morels; like theGyromitra, they are eaten by some and considered poisonous by others.[14]
The genusGyromitra had been classically considered part of the familyHelvellaceae, along with the similar-looking elfin saddles of the genusHelvella. Analysis of theribosomal DNA of many of thePezizales showedG. esculenta and the other false morels to be only distantly related to the other members of the Helvellaceae and instead most closely related to the genusDiscina, forming aclade which also containsPseudorhizina andHydnotrya. Thus the four genera are now included in the familyDiscinaceae.[15]
The genus name is derived from theGreek termsgyros/γυρος "round" andmitra/μιτρα "headband".[16] Its specific epithet is derived from theLatinesculentus, "edible".[17]
Resembling a brain, the irregularly shapedcap may be up to 10 centimetres (4 inches) high and 15 cm (6 in) wide. Initially smooth, it becomes progressively more wrinkled as it grows and ages. The cap colour may be various shades of reddish-, chestnut-, purplish-, bay-, dark or sometimes golden-brown; it darkens to black in age.[18] Specimens from California may have more reddish-brown caps.[6] Attached to the cap at several points, thestipe is3–6 cm (1–2+1⁄2 in) high and1–5 cm (1⁄2–2 in) wide.[19]G. esculenta has been reported to have a solid stipe whereas those of true morels (Morchella spp.) are hollow,[20] although a modern source says it is hollow as well.[18] The smell can be pleasant and has been described as fruity, and the fungus is mild-tasting.
Thespore print is whitish, with transparent spores that are elliptical and 17–22 μm in length.[21]
G. esculenta resembles the various species of true morel, although the latter are more symmetric and look more like pitted gray, tan, or brownsponges. Its cap is generally darker and larger.[22]
G. gigas,G. infula andG. ambigua in particular are similar,[19] the latter two being toxic to humans.[18]
G. esculenta grows on sandy soil intemperate coniferous forest and occasionally indeciduous woodlands. Among conifers it is mostly found under pines (Pinus spp.), but also sometimes under aspens (Populus spp.).[23] The hunting period is from April to July, earlier than for other species, and the fungus may even sprout up with the melting snow.[6] It can be abundant in some years and rare in others. The mushroom is more commonly found in places where ground has been disturbed, such as openings, rivulets, washes, timber clearings, plowed openings, forest fire clearings, and roadsides.[20] Enthusiasts in Finland have been reported burying newspaper inoculated with the fungus in the ground in autumn and returning the following spring to collect mushrooms.[24]
Although more abundant inmontane and northern coniferous woodlands such as theSierra Nevada and theCascade Range in northwestern North America,Gyromitra esculenta is found widely across the continent,[6] as far south asMexico.[25] It is also common inCentral Europe, less abundant in the east, and more in montane areas than lowlands.[7] It has been recorded fromNorthern Ireland,[26] fromUşak Province in Western Turkey,[27] and from the vicinity ofKaş in theAntalya Province of Turkey's southern coast.[28]
Toxic reactions have been known for at least a hundred years. Experts speculated the reaction was more of anallergic one specific to the consumer, or a misidentification, rather than innate toxicity of the fungus, due to the wide range in effects seen. Some would suffer severely or perish while others exhibited no symptoms after eating similar amounts of mushrooms from the same dish. Yet others would be not poisoned after eatingG. esculenta for many years.[29] However, the fungus is now widely recognized as potentially deadly.[30]
Gyromitra esculenta contains levels of the poisongyromitrin that vary locally among populations; although these mushrooms are only rarely involved in poisonings in eitherNorth America orwestern Europe, intoxications are seen frequently ineastern Europe andScandinavia.[31] A 1971 Polish study reported at the time that the species accounted for up to 23% of mushroom fatalities each year.[32] Death rates have dropped since the mid-twentieth century; inSweden poisoning is common, though life-threatening poisonings have not been detected and there was no fatality reported over the 50 years from 1952 to 2002.[33]Gyromitra poisonings are rare in Spain, due to the widespread practice of drying the mushrooms before preparation and consumption,[34]but has a mortality rate of about 25%[clarification needed].[35]
Alethal dose of gyromitrin has been estimated to be 10–30 mg/kg for children and 20–50 mg/kg in adults. These doses correspond to around 0.2–0.6 kg (7 oz – 1 lb 5 oz) and 0.4–1 kg (14 oz – 2 lb 3 oz) of fresh mushroom respectively.[36] Evidence suggests that children are more severely affected; it is unclear whether this is due to a larger weight consumed per body mass ratio or to differences in enzyme and metabolic activity.[37]
Populations ofG. esculenta appear to vary geographically in their toxicity. A French study has shown that mushrooms collected at higher altitudes have lower concentrations of toxin than those from lower elevations,[37] and there is some evidence that fungi west of theRocky Mountains in North America contain less toxin than those to the east.[38] However, poisonings in the USA have been reported,[39] although less frequently than in Europe.[40]
The identity of the toxic constituents eluded researchers until 1968, when acetaldehydeN-methyl-N-formylhydrazone, better known asgyromitrin, was isolated.[41] Gyromitrin is avolatile,water-solublehydrazine compound hydrolyzed in the body intoN-methyl-N-formylhydrazine (MFH) thenmonomethylhydrazine (MMH). OtherN-methyl-N-formylhydrazone derivatives have been isolated in subsequent research, although they are present in smaller amounts. These other compounds would also produce monomethylhydrazine when hydrolyzed, although it remains unclear how much each contributes to the false morel's toxicity.[42]
The toxins react withpyridoxal-5-phosphate—the activated form ofpyridoxine (vitamin B6)—and form ahydrazone. This reduces production of the neurotransmitterGABA via decreased activity ofglutamic acid decarboxylase,[43] producing the neurological symptoms. MMH also causesoxidative stress leading tomethemoglobinemia.[36] Inhibition ofdiamine oxidase (histaminase) elevateshistamine levels resulting in headaches, nausea, vomiting, and abdominal pain.[44]
MFH, as a mushroom component[45] and an intermediary product of gyromitrin hydrolysis,[46] has toxicities of its own. MFH undergoescytochrome P450-regulated oxidative metabolism which, via reactivenitrosamide intermediates, leads to formation ofmethyl radicals which lead to liver necrosis.[47][48]
The symptoms of poisoning are typicallygastrointestinal andneurological.[33] Symptoms occur within 6–12 hours of consumption, although cases of more severe poisoning may present sooner—as little as 2 hours after ingestion. Initial symptoms are gastrointestinal, with sudden onset ofnausea, vomiting, and waterydiarrhea whichmay be bloodstained.Dehydration may develop if the vomiting or diarrhea is severe. Dizziness, lethargy,vertigo, tremor,ataxia,nystagmus, and headaches develop soon after;[33]fever often occurs, a distinctive feature which does not develop after poisoning by other types of mushrooms.[49] In most cases of poisoning, symptoms do not progress from these initial symptoms, and patients recover after 2–6 days of illness.[32]
In some cases there may be anasymptomatic phase following the initial symptoms which is then followed by more significant toxicity includingkidney damage,[50]liver damage, andneurological dysfunction including seizures and coma.[36] These signs usually develop within 1–3 days in serious cases.[33] The patient developsjaundice andthe liver andspleen become enlarged; in some casesblood sugar levels will rise (hyperglycemia) and then fall (hypoglycemia) and liver toxicity is seen. Additionally intravascularhemolysis causes destruction of red blood cells resulting in increase in free hemoglobin andhemoglobinuria which can lead to renal toxicity orkidney failure.Methemoglobinemia may also occur in some cases. This is where higher than normal levels ofmethemoglobin, which is a form of hemoglobin that can not carry oxygen, are found in the blood. It causes the patient to become short of breath andcyanotic.[51] Cases of severe poisoning may progress to a terminal neurological phase, withdelirium, musclefasciculations and seizures, andmydriasis progressing tocoma, circulatory collapse, andrespiratory arrest.[52] Death may occur from five to seven days after consumption.[53]
Treatment is mainlysupportive; gastric decontamination withactivated charcoal may be beneficial if medical attention is sought within a few hours of consumption. However, symptoms often take longer than this to develop, and patients do not usually present for treatment until many hours after ingestion, thus limiting its effectiveness.[54] Patients with severe vomiting or diarrhea can be rehydrated withintravenous fluids.[32] Monitoring of biochemical parameters such as methemoglobin levels, electrolytes, liver and kidney function,urinalysis, andcomplete blood count is undertaken and any abnormalities are corrected.Dialysis can be used if kidney function is impaired or the kidneys are failing. Hemolysis may require ablood transfusion to replace the lost red blood cells, whilemethemoglobinemia is treated with intravenousmethylene blue.[55]
Pyridoxine, also known asvitamin B6, can be used to counteract theinhibition by MMH on the pyridoxine-dependent step in the synthesis of the neurotransmitterGABA. Thus GABA synthesis can continue and symptoms are relieved.[56] Pyridoxine, which is only useful for the neurological symptoms and does not decrease hepatic toxicity,[48][57] is given at a dose of 25 mg/kg; this can be repeated up to a maximum total of 15 to 30 g daily if symptoms do not improve.[58]Benzodiazepines are given to control seizures; as they also modulate GABA receptors they may potentially increase the effect of pyridoxine. Additionally MMH inhibits the chemical transformation offolic acid into its active form,folinic acid, this can be treated by folinic acid given at 20–200 mg daily.[36]
Lagrangeet al. presented in 2018 a link between life-long foraging forG. esculenta andamyotrophic lateral sclerosis (ALS) in French Alps populations.[59] Similar ALS clusters possibly related to mushrooms are found near theAosta Valley (Italy), inSardinia, and inMichigan.[3]
Monomethylhydrazine,[60] gyromitrin,[61] rawGyromitra esculenta,[62] andN-methyl-N-formylhydrazine[45][63] have been shown to becarcinogenic in experimental animals. AlthoughGyromitra esculenta has not been observed to cause cancer in humans,[64] it is possible there is a carcinogenic risk for people who ingest these types of mushrooms.[45] Even small amounts may have a carcinogenic effect.[65] At least 11 different hydrazones have been isolated fromG. esculenta, and it is not known if all potential carcinogens can be completely removed by parboiling.[66]
Despite its recognized toxicity,G. esculenta is marketed and consumed in several countries or states in Europe and North America. It was previously consumed in Germany, with fungi picked in and exported fromPoland; more recently, however, Germany andSwitzerland discouraged consumption by prohibiting its sale.[21][64] Similarly inSweden, theSwedish National Food Administration warns that it is not fit for human consumption,[67] and restricts purchase of fresh mushrooms to restaurants alone.[68] The mushroom is still highly regarded and consumed inBulgaria, being sold in markets and picked for export there.[69] In some countries such as Spain, especially in the easternPyrenees, they are traditionally considered a delicacy, and many people report consuming them for many years with no ill effects.[70] Despite this, the false morel is listed as hazardous in official mushroom lists published by the Catalan Government[12] and sale to the public is prohibited throughout Spain.[71] Outside of Europe,G. esculenta is consumed in theGreat Lakes region and some western states in the United States.[72]
Selling and purchasing fresh false morels is legal in Finland, where it is highly regarded.[73] However, the mushrooms are required by law to be accompanied with a warning that they are poisonous and legally prescribed preparation instructions.[74] False morels are also sold prepared and canned, in which case they are ready to be used. Official figures from the Finnish Ministry of Agriculture and Forestry report a total amount of false morels sold in Finland of 21.9 tonnes in 2006 and 32.7 tonnes, noted as being above average, in 2007.[75] In 2002, the Finnish Food Safety Authority estimated annual consumption of false morels to be hundreds of tonnes in plentiful years.[76] InFinnish cuisine, false morels may be cooked in anomelette, or gentlysautéed in butter in a saucepan, flour and milk added to make abéchamel sauce, or pie filling. Alternatively, more fluid can be added for a false morel soup. Typical condiments added for flavour includeparsley,chives,dill andblack pepper.[77][78]
While cooking the fungus removes (most of) the toxins, the cook can become poisoned by thehydrazine fumes given off by cooking.[79]
In 2015, Swedish chefPaul Svensson [sv] caused a controversy when he prepared a dish withGyromitra esculenta in a TV show. Mushroom expert Monica Svensson criticized him for including it, becausemonomethylhydrazine is a known carcinogen and there is a risk that inexperienced people might misinterpret the recipe and omit the steps that reduce the toxicity level. She also expressed criticism toPer Morberg for similar reasons. Paul Svensson said that he was not aware of the carcinogenic effects and apologized afterwards, and he promised to removeGyromitra from his dishes.[80]
Most of the gyromitrin must be removed to render false morels edible. The recommended procedure involves either first drying and then boiling the mushrooms, or boiling the fresh mushrooms directly.[81] To prepare fresh mushroom it is recommended that they are cut into small pieces andparboiled twice in copious amounts of water, at least three parts water to one part chopped mushrooms, for at least five minutes, after each boiling the mushroom should be rinsed thoroughly in clean water.[81] Each round of parboiling reduces the free gyromitrin contents to a tenth.[82] Significant amounts of gyromitrin are retained in the internal structure of the mushroom even after boiling. After 3 rounds of boiling for 5 minutes and discarding the water, the gyromitrin content is reduced to 6-15% of the original. After 5 rounds, this content is reduced to 7%.[83] The gyromitrin is leached into the water where it will remain, therefore the parboiling water must be discarded and replaced with fresh water after eachround of boiling. However, it is still recommended that the mushroom be boiled after drying.[81]
MMH boils at 87.5 °C (190 °F) and thus readily vaporizes into the air when water containing fresh false morels is boiled.[39] If boiling the mushrooms indoors, care should be taken to ensure adequate ventilation, and, if symptoms of monomethylhydrazine poisoning appear, immediately open all windows and move outside to seek fresh air.[84] Even after boiling, small amounts of gyromitrin and other hydrazine derivatives remain in the mushrooms. Given the possibility of accumulation of toxins,[how?] repeated consumption is not recommended.[85]
Strains with much lower concentrations of gyromitrin have been discovered, and the fungus has been successfully grown to fruiting in culture.[86] Thus there is scope for future research into cultivation of safer strains.[87]
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