Gyromitra esculenta

Source: Wikipedia, the free encyclopedia.
Several terms redirect here. For other mushroom species sometimes referred to as "lorchels" or "false morels", see false morel.

Gyromitra esculenta
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Pezizomycetes
Order: Pezizales
Family: Discinaceae
Genus: Gyromitra
Species:
G. esculenta
Binomial name
Gyromitra esculenta
(Pers. ex Pers.) Fr. (1849)
Synonyms[1]
  • Helvella esculenta Pers. (1800)
  • Boud.
    (1907)
Gyromitra esculenta
View the Mycomorphbox template that generates the following list
Smooth hymenium
Cap is convex
Hymenium attachment is not applicable
Stipe is bare
Spore print is yellow to buff
Ecology is
saprotrophic
 or
mycorrhizal
Edibility is deadly or choice

Gyromitra esculenta

coniferous trees in spring and early summer. The fruiting body, or mushroom, is an irregular brain-shaped cap dark brown in colour that can reach 10 centimetres (4 inches) high and 15 cm (6 in) wide, perched on a stout white stipe
up to 6 cm (2+1⁄2 in) high.

Although potentially fatal if eaten raw (causing restrictions on its sales in some areas), G. esculenta is still commonly

hydrolyzed into the toxic compound monomethylhydrazine, which affects the liver, central nervous system, and sometimes the kidneys. Symptoms of poisoning involve vomiting and diarrhea several hours after consumption, followed by dizziness, lethargy and headache. Severe cases may lead to delirium
, coma, and death after five to seven days.

Taxonomy

The fungus was first described in 1800, by

Christian Hendrik Persoon, as Helvella esculenta,[3] and gained its current accepted binomial name when the Swedish mycologist Elias Magnus Fries placed it in the genus Gyromitra in 1849.[4] The genus name is derived from the Greek terms gyros/γυρος "round" and mitra/μιτρα "headband".[5] Its specific epithet is derived from the Latin esculentus, "edible".[6]

It is known by a variety of common descriptive names such as "brain mushroom",[7] "turban fungus",[8] elephant ears,[9] or "beefsteak mushroom/morel", although beefsteak mushroom can also refer to the much less toxic basidiomycete Fistulina hepatica.[10] Dating from the 19th century, the German term lorchel is a result of the older lorche, itself from the 18th century Low German Lorken, aligning with the similar-sounding (and similar-looking) morchel.[11][12]

Gyromitra esculenta is a member of a group of fungi known as "

G. 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.[13] The toxic qualities of G. esculenta may be reduced by cooking, but possibly not enough to prevent poisoning from repeated consumption.[14]

The more distantly related ascomycete mushrooms of the genus Verpa, such as V. bohemica and V. conica, are also known as false morels, early morels or thimble morels; like the Gyromitra, they are eaten by some and considered poisonous by others.[15]

The genus Gyromitra had been classically considered part of the family Helvellaceae, along with the similar-looking elfin saddles of the genus Helvella. Analysis of the ribosomal DNA of many of the Pezizales showed G. 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 genus Discina, forming a clade which also contains Pseudorhizina and Hydnotrya. Thus the four genera are now included in the family Discinaceae.[16]

Description

A younger specimen with a less wrinkled cap

Resembling a brain, the irregularly shaped

μm in length.[20]

Similar species

G. esculenta resembles the various species of true morel, although the latter are more symmetric and look more like pitted gray, tan, or brown sponges. Its cap is generally darker and larger.[21]

G. gigas, G. infula and

G. ambigua in particular are similar,[18] the latter two being toxic to humans.[17]

Distribution and habitat

G. esculenta grows on sandy soil in temperate coniferous forest and occasionally in deciduous woodlands. Among conifers it is mostly found under pines (Pinus spp.), but also sometimes under aspen (Populus spp.).[22] The hunting period is from April to July, earlier than for other species, and the fungus may even sprout up with the melting snow.[7] 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.[19] 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.[23]

Although more abundant in

montane and northern coniferous woodlands such as the Sierra Nevada and the Cascade Range in northwestern North America, Gyromitra esculenta is found widely across the continent,[7] as far south as Mexico.[24] It is also common in Central Europe, less abundant in the east, and more in montane areas than lowlands.[8] It has been recorded from Northern Ireland,[25] from Uşak Province in Western Turkey,[26] and from the vicinity of Kaş in the Antalya Province of Turkey's southern coast.[27]

Toxicity

For sale with warning sign, Market Square, Helsinki

Toxic reactions have been known for at least a hundred years. Experts speculated the reaction was more of an

allergic 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 eating G. esculenta for many years[28] However, the fungus is now widely recognized as potentially deadly.[29]

Gyromitra esculenta contains levels of the poison gyromitrin that vary locally among populations; although these mushrooms are only rarely involved in poisonings in either North America or western Europe, intoxications are seen frequently in eastern Europe and Scandinavia.[30] A 1971 Polish study reported at the time that the species accounted for up to 23% of mushroom fatalities each year.[31] Death rates have dropped since the mid-twentieth century; in Sweden 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.[32] Gyromitra poisonings are rare in Spain, due to the widespread practice of drying the mushrooms before preparation and consumption,[33] but has a mortality rate of about 25%.[34]

A lethal 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.[35] 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.[36]

Geographical variation

Populations of G. 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,[36] and there is some evidence that fungi west of the Rocky Mountains in North America contain less toxin than those to the east.[37] However, poisonings in the USA have been reported,[38] although less frequently than in Europe.[39]

Biochemistry

MMH (C H3N2H3), a toxic metabolite

The identity of the toxic constituents eluded researchers until 1968, when acetaldehyde N-methyl-N-formylhydrazone, better known as

water-soluble hydrazine compound hydrolyzed in the body into N-methyl-N-formylhydrazine (MFH) then monomethylhydrazine (MMH). Other N-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.[41]

The toxins react with

glutamic acid decarboxylase,[42] producing the neurological symptoms. MMH also causes oxidative stress leading to methemoglobinemia.[35] Inhibition of diamine oxidase (histaminase) elevates histamine levels resulting in headaches, nausea, vomiting, and abdominal pain.[43]

MFH, as a mushroom component[44] and an intermediary product of gyromitrin hydrolysis,[45] has toxicities of its own. MFH undergoes cytochrome P450-regulated oxidative metabolism which, via reactive nitrosamide intermediates, leads to formation of methyl radicals which lead to liver necrosis.[46][47]

Symptoms

The symptoms of poisoning are typically

nystagmus, and headaches develop soon after;[32] fever often occurs, a distinctive feature which does not develop after poisoning by other types of mushrooms.[48] In most cases of poisoning, symptoms do not progress from these initial symptoms, and patients recover after 2–6 days of illness.[31]

In some cases there may be an

cyanotic.[50] Cases of severe poisoning may progress to a terminal neurological phase, with delirium, muscle fasciculations and seizures, and mydriasis progressing to coma, circulatory collapse, and respiratory arrest.[51] Death may occur from five to seven days after consumption.[52]

Treatment

Treatment is mainly

intravenous fluids.[31] Monitoring of biochemical parameters such as methemoglobin levels, electrolytes, liver and kidney function, urinalysis, and complete 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 a blood transfusion to replace the lost red blood cells, while methemoglobinemia is treated with intravenous methylene blue.[54]

Pyridoxine, also known as

folic acid into its active form, folinic acid, this can be treated by folinic acid given at 20–200 mg daily.[35]

Long-term effects

ALS

Lagrange et al. presented in 2018 a link between life-long foraging for G. esculenta and

amyotrophic lateral sclerosis (ALS) in French Alps populations.[58] Similar ALS clusters possibly related to mushrooms are found near the Aosta Valley (Italy), in Sardinia, and in Michigan.[59]

Carcinogenicity

Monomethylhydrazine,[60] gyromitrin,[61] raw Gyromitra esculenta,[62] and N-methyl-N-formylhydrazine[44][63] have been shown to be carcinogenic in experimental animals. Although Gyromitra 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.[44] Even small amounts may have a carcinogenic effect.[65] At least 11 different hydrazones have been isolated from G. esculenta, and it is not known if all potential carcinogens can be completely removed by parboiling.[66]

Consumption

For sale in Helsinki, Finland with compulsory preparation instructions/safety datasheet

Despite its recognized toxicity, Gyromitra 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 from

Swedish 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 in Bulgaria, being sold in markets and picked for export there.[69] In some countries such as Spain, especially in the eastern Pyrenees, 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[13] and sale to the public is prohibited throughout Spain.[71] Outside of Europe, G. esculenta is consumed in the Great 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.

sautéed in butter in a saucepan, flour and milk added to make a béchamel sauce, or pie filling. Alternatively, more fluid can be added for a false morel soup. Typical condiments added for flavour include parsley, chives, dill and black pepper.[77][78]

While cooking the fungus removes (most of) the toxins, the cook can become poisoned by the hydrazine fumes given off by cooking.[79]

Controversies

In 2015, Swedish chef Paul Svensson [sv] caused a controversy when he prepared a dish with Gyromitra esculenta in a TV show. Mushroom expert Monica Svensson criticized him for including it, because monomethylhydrazine 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 to Per Morberg for similar reasons. Paul Svensson said that he was not aware of the carcinogenic effects and apologized afterwards, and he promised to remove Gyromitra from his dishes.[80]

Preparation

cream sauce

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.

parboiled 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 each round 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.[38] Poorly ventilated spaces allow vapor to accumulate, resulting in gyromitrin poisoning. If boiling the mushrooms indoors, care should be taken to ensure adequate ventilation, and, if symptoms of gyromitrin poisoning appear, immediately seek fresh air.[84] Even after boiling, small amounts of gyromitrin remain in the mushrooms. Given the possibility of accumulation of toxins,[how?] repeated consumption is not recommended.[85]

Prospects for cultivation

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]

See also

  • List of deadly fungi

References

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