KingdomFungiGenusGyromitraSpeciesesculenta
Gyromitra esculenta
T3 · LethalPublished 2026-09-18Spring
The false morel is the most widely eaten poisonous mushroom in Europe, which is a statement about cultural habit rather than about chemistry. It contains gyromitrin, a volatile compound that hydrolyses to monomethylhydrazine — a hepatotoxin of the same order of hazard as the amatoxins — and the vapour released during cooking is itself toxic.
Block 01 · Record
Telling it from a true morel
Cut the head in half lengthwise. A true morel has a head of vertical ridges enclosing deep pits, and the interior is a single hollow cavity running unbroken from the stem through to the apex. Gyromitra esculenta has a brain-like head of gyrose folds that never enclose a pit, the head is lobed and partly free from the stem, and the stem is a separate hollow tube that may contain debris. The two never share a season in the same week: gyromitrin-bearing Gyromitra fruits in spring, often on burnt or disturbed sandy ground under pines, from April to early June, while morels follow a slightly later and more protracted window.
Spores and the two oil drops
Spores are 18-22 x 9-12 micrometres, broadly ellipsoid to oblong, smooth, thin-walled, and each carries two large oil drops that nearly fill the interior. They are discharged from asci rather than basidia, so the deposit is white to pale cream and forms a fine powder rather than the coarser deposit of an agaric. They are inamyloid and acyanophilic, and the oil drops show clearly as refractile bodies in cotton blue.
Gyromitrin, volatility and the cooking myth
Gyromitrin hydrolyses in the body to monomethylhydrazine, which depletes pyridoxine and disrupts GABA metabolism, producing vomiting, seizures and hepatic injury. The critical fact is that the compound is volatile: it boils off during cooking, which is why the traditional method of parboiling in an open pan and discarding the water reduces the dose, and also why the vapour has poisoned people who never ate the mushroom at all by inhaling it in a closed kitchen. The dose also varies by a factor of ten between collections and between cooking batches, so a method that appeared to work for years can fail on a single pan.
Habitat, season and who is at risk
The species is a spring ascomycete of sandy, often podzolic conifer soil and it responds to disturbance: forest fire sites, cleared tracks, gravel pits and the sandy shoulders of forest roads are the classic sites, and it appears in the first two springs after a fire. Children are disproportionately affected because the dose that produces seizures is much lower in a small body, and the latency of six to twelve hours means the meal is rarely suspected as the cause.
Points to carry to the bench
- Cut the head lengthwise: a continuous hollow cavity from stem to apex means a true morel; gyrose folds that never enclose a pit mean Gyromitra.
- Spores 18-22 micrometres with two large oil drops, from asci, not basidia.
- Gyromitrin is volatile — the cooking vapour is toxic in a closed kitchen, and dose varies tenfold between batches.
- Fruits in spring on burnt or disturbed sandy ground under pines; latency is 6-12 hours, so the meal is rarely suspected.
| Cap | shape: Irregularly lobed and convoluted, brain-like, 30-100 mm across, occasionally 150 mm; the lobes are rounded in section and never enclose a cavity that opens to the outside.surface: Reddish-brown to dark chestnut-brown, dull, with a finely granular to waxy texture that dries to a brittle crust.margin: Lobed, wavy and often partly free from the stem; the margin is not differentiated from the rest of the head. |
|---|---|
| Gills | attachment: None — this is an ascomycete. The fertile layer lines the outside of the folded head as a thin hymenium, and there is no gill, pore or spine structure at any stage.spacing: Not applicable; the folds of the head are 3-8 mm deep and do not contain spores, which are produced on the outer surface alone.edge: Not applicable; the fold edges are rounded and sterile. |
| Spore print | Broadly ellipsoid to oblong, smooth, thin-walled, with two large oil drops — one at each pole — that nearly fill the spore.Smooth and inamyloid; the spores are roughly twice the length of a morel spore. |
| Habitat and season | Saprotrophic on sandy, often podzolic soil under conifers, above all under pines; strongly associated with disturbed and burnt ground, forest fire sites, cleared tracks, gravel pits and the sandy banks of forest roads. Fruits alone or in small groups. |
Block 02 · Chemistry
| Reagent | Verdict | Reaction | Weight |
|---|---|---|---|
 MELZ | inamyloid | Spore wall and the ascus tips stay pale yellow; no blue-black amyloid reaction in either. | 3.00 |
 COTTON | acyanophilic | Spores remain unstained; the two oil drops show as clear refractile bodies against the blue background. | 2.00 |
 KOH5 | negative | Head surface darkens slightly and the crust softens; no yellow, green or red development. | 2.00 |
 FESO4 | negative | Stem flesh and head tissue unchanged after 90 s. | 3.00 |
Injury stain None. The head and stem keep their colour after cutting; the brown staining that appears on old specimens is decay, not a reaction to injury.
Block 03 · Confusion
| Separating character | This record | Confused with |
|---|---|---|
| A head built of true vertical ridges enclosing deep pits, attached to the stem at a single basal point; cut it lengthwise and the cavity runs unbroken from stem to apex. Gyromitra folds never enclose a pit and the head is lobed and partly free. | Gyromitra esculentaT3 | Morchella esculenta▲ +3 |
| A thimble-shaped head attached only at the very apex of the stem, with the whole skirt hanging free; it is T1 rather than T3 but shares the spring, sandy-soil habitat. | Gyromitra esculentaT3 | Verpa bohemica▲ +2 |
| A larger, paler, more regularly lobed head that is also reported to contain gyromitrin; treated as the same hazard despite a long history of being eaten. | Gyromitra esculentaT3 | Gyromitra gigas▲ +0 |
Toxicity ladder
A single meal of a normal-sized fruit body has killed, or the toxin class (amatoxins, orellanine, gyromitrin, severe muscarine load) is documented as lethal in humans. T3 does not mean every meal kills — it means the margin between a meal and a fatal dose is not wide enough to plan around, and there is no field test that measures it.
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