Gyromitra esculenta

Gyromitra esculenta is an ascomycete fungus from the genus Gyromitra. 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. It is widely distributed across Europe and North America, normally fruiting in sandy soils under coniferous trees in spring and early summer.

Although potentially fatal if eaten raw, G. esculenta is sometimes parboiled for consumption, being a popular delicacy in Europe and the upper Great Lakes region of North America. However, evidence suggests that thorough cooking does not eliminate all toxins. When consumed, the principal active mycotoxin, gyromitrin, is hydrolyzed into the toxic compound monomethylhydrazine, which affects the liver, central nervous system, and sometimes the kidneys. Symptoms involve vomiting and diarrhea several hours after consumption, followed by dizziness, lethargy and headache. Severe cases may lead to delirium, coma, and death. Recent evidence suggests G. esculenta may be chronically toxic and linked to regional clusters of ALS.

Taxonomy

The fungus was first described in 1800, by mycologist Christian Hendrik Persoon, as Helvella esculenta, and gained its current accepted binomial name when the Swedish mycologist Elias Magnus Fries placed it in the genus Gyromitra in 1849.

It is known by a variety of common descriptive names such as "brain mushroom", "turban fungus", elephant ears, or "beefsteak mushroom/morel", although beefsteak mushroom can also refer to the much choicer edible basidiomycete Fistulina hepatica. 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.

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 genus Morchella. The grouping includes other species of the genus Gyromitra, such as G. infula (elfin saddle), G. caroliniana and 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. The toxic qualities of G. esculenta may be reduced by cooking, but possibly not enough to prevent poisoning from repeated consumption.

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.

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.

Etymology

The genus name is derived from the Greek terms gyros/γυρος "round" and mitra/μιτρα "headband". Its specific epithet is derived from the Latin esculentus, "edible".

Description

Resembling a brain, the irregularly shaped cap may be 12 centimetres (4+1⁄2 inches) or more high and wide. Initially smooth, it becomes progressively more wrinkled as it grows and ages. The cap is brownish, and can variously be shaded reddish, chestnut, purplish, or golden. It darkens to black in age. Specimens from California may have more reddish-brown caps. Attached to the cap at several points, the stipe is 3–6 cm (1–2+1⁄2 in) high and 1–5 cm (1⁄2–2 in) wide. G. esculenta has been reported to have a solid stipe whereas those of true morels (Morchella spp.) are hollow, although a modern source says it is hollow as well. The smell can be pleasant and has been described as fruity, and the fungus is mild-tasting.

The spore print is whitish, with transparent spores that are elliptical and 17–22 μm in length.

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.

G. gigas, G. infula and G. ambigua in particular are similar, the latter two being toxic to humans.

Habitat and distribution

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 aspens (Populus spp.). The hunting period is from April to July, earlier than for other species, and the fungus may even sprout up with the melting snow. 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. 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.

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, as far south as Mexico. It is also common in Central Europe, less abundant in the east, and more in montane areas than lowlands. It has been recorded from Northern Ireland, from Uşak Province in Western Turkey, and from the vicinity of Kaş in the Antalya Province of Turkey's southern coast.

Toxicity

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. However, the fungus is now widely recognized as potentially deadly.

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. A 1971 Polish study reported at the time that the species accounted for up to 23% of mushroom fatalities each year. 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. Gyromitra poisonings are rare in Spain, due to the widespread practice of drying the mushrooms before preparation and consumption, but has a mortality rate of about 25%.

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. 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.

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