There are, according to current estimates, 209 species of hallucinogenic mushroom, of which most fall into two broad groups.2 The first contains the fly-agaric, Amanita muscaria, and its close relative the panther cap, Amanita pantherina. The former is the red-and-white-spotted mushroom so familiar to us from childhood, where it appears ubiquitously in storybook illustrations as the preferred seating of gnomes; the latter is its less well-known brown-and-white-spotted cousin. Both fungi are closely related to the deadliest of species, the Destroying Angel, Amanita virosa, and the Death Cap, Amanita phalloides (which, as their names suggest, are responsible for the majority of fatalities worldwide).

The fly-agaric is not deadly, however, but contains a fuzzy cocktail of different chemical alkaloids, including ibotenic acid (α-amino-3-hydroxy-5-isoxazoleacetic acid) and muscimol (5- (aminomethyl)-3-hydroxyisoxazole), which produce an unsteady set of symptoms: nausea, dizziness, a flushed countenance, twitchiness, increased stamina, euphoria, deep coma-like sleep, hallucinatory dreams and, occasionally, nothing but a headache the next day.

Not surprisingly given this litany, both species have been largely shunned apart from, that is, in two areas of Siberia where there is a long tradition of using fly-agaric as an intoxicant. Nevertheless, this mushroom has generated a spectacular array of myths and legends about its supposed role in the origins of shamanism and religion – so many myths, in fact, that three chapters in the middle section of this book are devoted to exploring and unpicking them. Curiously, the fly-agaric seems to be the one mushroom that most people assiduously avoid, and yet it is the one concerning which people will happily countenance all manner of moonshine. Something about its colourful and memorable form makes the mere thought of it a potent catalyst for the human imagination, but just like its genuine, capricious, psychoactive effects, these tall tales need to be approached with a good deal of caution.

The second group comprises those fungi, most commonly within the genus Psilocybe, that contain the active alkaloid ingredients psilocybin (4-phosphoryloxy-N, N-dimethyltryptamine) and psilocin (4-hydroxy-N, N-dimethyltryptamine): these are the ones that we typically mean by the term ‘magic mushrooms’ and that constitute the main subject of this book.3 There are currently 186 known psilocybin species – the figure is rising all the time – of which 76 occur in Mexico alone.4 To pick a mushroom at random in Mexico is to stand a very good chance of picking a hallucinogenic one, which is probably why it is the one part of the world where there is a genuinely old tradition of psilocybin mushroom usage. There are far too many psilocybin mushrooms to describe them all here, but of the plethora growing worldwide two deserve special mention.

The first is the Liberty Cap, or Psilocybe semilanceata (naked head, half-lance shaped). In Britain this delicate little mushroom appears in the autumn months, growing in great abundance in ‘troops’. It is found in pastures across the British Isles, but especially in acid upland pastures, the wet, chilly sheep fields of Wales, the Pennines, Devon and Cornwall, and Scotland. Somewhat parochially, we think of it as ‘our’ magic mushroom, but in fact it grows in many temperate regions across the world. It is found across western Europe, from Scandinavia in the north to the Spanish Picos mountains in the south; from Ireland in the west to the Czech Republic and Russia in the east. Moreover, it grows across great swathes of the American Pacific Northwest, and also in New Zealand and Tasmania. Contrary to popular wisdom, it is not coprophilic, that is it is not a dung-lover, but actually grows saprophytically upon the dead root cells of certain grasses.5 Despite its small size – the cap is only about a centimetre across – it is home not to gnomes but to species of mycophagous sciarid flies, the grubs of which are familiar to anyone who has ever picked and dried the mushrooms.

Though originally lumped together with other small, nondescript fungi as Agaricus glutinosus (in the eighteenth century Agaricus was a catch-all generic name for mushrooms), the species was finally identified, and acquired its Latin epithet, when it was described by the great pioneer of fungal taxonomy, the Swedish mycologist Elias Magnus Fries (1794–1878). Since then it has acquired many common names, especially since it revealed itself to be a hallucinogenic species during the 1970s: mushrooms, shrooms, mushies, psillys, pixie caps, Welsh friends, Welsh tea. It is most commonly known as the Liberty Cap because of the distinctive shape of its cap, which resembles the Phrygian bonnets worn by the French revolutionaries when they stormed the Bastille. It seems to have acquired this name in Britain during the late eighteenth or early nineteenth century, perhaps in response to palpable anxieties surrounding the very real possibility of a Napoleonic invasion: the sudden overnight appearance of troops of Liberty Caps might very well have been taken as an unwelcome portent of a similar incursion by the French. These days, and somewhat tellingly, it is the mushroom’s resemblance to the archetypal goblin’s cap that particularly arrests attention. This iconic shape made it a potent countercultural badge during the 1980s and 1990s, when it appeared on T-shirts, postcards and album covers.

As luck would have it, this one species that grows so abundantly in the world happens also to contain a high and predictable concentration of psilocybin: about 1 per cent. It contains trivial amounts of psilocin, but significant amounts (0.36 per cent) of another psychoactive alkaloid, baeocystin (4-phosphoryloxy-N-methyltryptamine).6 Were these concentrations not so stable, dosage would be impossible to gauge (as is the case with certain other psychoactive species) and the mushroom would probably not have been adopted as a psychoactive drug. As it is, any twenty mushrooms picked in different parts of the world will have, on average, the same concentration of active ingredients, and therefore the same pharmacological effect.

The second notable psilocybin mushroom is Psilocybe cubensis. It was first collected by the American mycologist Franklin Sumner Earle (1856–1929) in 1904 in Cuba, hence its species epithet (although he originally placed it in the genus Stropharia). It is much larger than its diminutive cousin, its distinctive golden-brown flying-saucer-shaped cap reaching sizes of up to eight centimetres across. It most definitely is coprophilic, and sprouts from the dung of bovines, or from well-manured ground, throughout the semi-tropical regions of the world. It is found in the south-east United States especially Florida, Louisiana and Mississippi; in Mexico, Cuba and the northernmost countries of South America; in Australia, notably Queensland; and in India and South East Asia, especially Vietnam and Thailand. The introduction of cattle-farming (usually through Western imperialist expansion) has undoubtedly done much to increase the frequency of occurrence of cubensis around the world. Whether cattle-farming actually spread the mushroom to new countries, or simply provided the already occurring species with a brand-new ecological habitat to colonise, is unknown. But what makes this species so important is that it has proved the easiest to cultivate: most of the magic mushrooms bought and sold, or grown in home terrariums, are cubensis.

Though different strains of cubensis exist, and cultivated mushrooms are marketed as such – for example ‘Thai’, ‘Colombian’, ‘Ecuadorian’ and so on – the commercial varieties are more often than not identical. Every mycelium produces several ‘flushes’ of mushrooms, which can be made to look different by varying the watering regime, or the time when they are harvested: selling these as different strains is simply a marketing trick to meet consumer expectations – shaped by the cannabis trade – of variety and choice.

Psilocybe cubensis is known by a variety of names. In Mexico, where it is sometimes viewed suspiciously because of its coprophilic habit, it is known as San Isidro Labrador after the patron saint of ploughing. In Mazatec it is...