Never eat a wild mushroom identified only from a website, a book or an app. Have every find checked in person by an expert, such as a mycological society.
Identification
Coprinopsis atramentaria, long known as Coprinus atramentarius, grows in dense clusters from buried wood, roots or stumps. Young caps are egg-shaped, opening to a bell or cone 3–7 cm across. The cap is grey to grey-brown, sometimes with a slightly darker, finely scaly centre, and marked by fine radial grooves towards the margin.
The gills are free and crowded, white at first, then turning purplish-brown to black. Like other ink caps, the mature cap autodigests: the gills and cap edge dissolve from the margin upwards into a black, ink-like liquid that carries the spores. The stem is white, hollow and fragile, with a faint ring-like zone near the base. The spore print is black; spores are smooth and ellipsoid with a germ pore.
The species belongs to the family Psathyrellaceae and is not closely related to the shaggy ink cap, Coprinus comatus, despite their shared ability to dissolve into ink.
Habitat and ecology
The common ink cap is a saprotrophic fungus that breaks down buried wood and other organic matter. It is common in gardens, parks, lawns, roadsides, building sites and woodland clearings, especially around stumps and where wood or roots lie beneath the soil. It can fruit from spring to late autumn, often appearing suddenly after rain, and the fruit bodies last only a day or two before dissolving.
It is widespread in Europe, North America and other temperate regions and is often found close to houses, which increases the chance that people pick it.
Uses and importance
The ink produced by the dissolving caps was historically used as a writing and drawing ink, which gave the group the name ink caps.
Its main importance today is in toxicology. The fruit bodies contain coprine, an unusual amino acid. In the body, a metabolite of coprine inhibits aldehyde dehydrogenase, the enzyme that breaks down acetaldehyde formed from alcohol. If alcohol is present, acetaldehyde accumulates and causes the so-called coprine syndrome, a reaction similar to that caused by the drug disulfiram. The effect can persist for several days after the mushroom meal, so alcohol taken long after the meal can still trigger symptoms.
Coprine has been studied as a pharmacological tool, but it has not been developed into a medicine, partly because of concerns raised in animal studies.
Safety and edibility
Fungaris classifies the common ink cap as toxic and does not recommend eating it. The reaction occurs when alcohol is consumed shortly before, together with, or for several days after the meal, and alcohol may be hidden in sauces, desserts or medicines.
Symptoms typically begin within minutes to a couple of hours of drinking alcohol and include facial flushing, a feeling of heat, a fast or pounding heartbeat, headache, nausea, vomiting, sweating and dizziness, sometimes with a drop in blood pressure. The reaction can be dangerous for people with heart disease. Anyone who develops these symptoms after eating ink caps, or who has eaten an unidentified mushroom, should seek emergency medical help immediately and keep any remains.
Never rely on a website, app or photo to identify a wild mushroom; have every find checked in person by an expert such as a mycological society or a trained mushroom adviser.
If you suspect mushroom poisoning, call your local emergency number or poison centre straight away, even before any symptoms appear, and keep the remains of the mushrooms.
Look-alikes
The shaggy ink cap (Coprinus comatus) is tall and cylindrical, white with shaggy, upturned scales, and grows singly or in groups in grass rather than in tight grey clusters on wood; it is not known to contain coprine. Other grey ink caps, such as Coprinopsis romagnesiana (with brownish scales) and Coprinellus species like the glistening ink cap (Coprinellus micaceus), can also be confused. Because grey ink caps are difficult to separate and their chemistry is not fully known, they should not be eaten unless an expert has confirmed the species in person.
Around the world
The common ink cap is found throughout temperate regions of Europe, Asia and North America and has been introduced elsewhere with soil and wood. Poisonings are reported in many countries when people mistake it for the shaggy ink cap or eat it without knowing about the alcohol interaction.
