A short history of the liberty cap, from Green Park to Class A

The liberty cap's recorded history begins in London in 1799, when a family ate mushrooms picked in Green Park and was taken ill. The species was named by the Swedish mycologist Elias Fries in 1838, its psilocybin was found in 1963, and in 2005 the United Kingdom made the fresh mushroom a Class A drug. Its common name is older and political: it comes from the cap of liberty of the French and American revolutions.

The name

The cap is shaped like a Phrygian cap, the soft conical hat that became a symbol of freedom in the 18th century and was hoisted on liberty poles; the mushroom's long thin stem completes the picture. The Latin name for that cap, pileus, is still the technical word mycologists use for a mushroom's cap (species account).

The scientific name is descriptive too. Psilocybe comes from the Greek for "bare head", referring to the smooth cap. The epithet semilanceata means "half spear-shaped".

1799: Green Park

The first reliable report of a liberty cap intoxication was published by the chemist Augustus Everard Brande in The Medical and Physical Journal in 1799. A man had gathered small mushrooms in Green Park in London and prepared a meal with them for his family. The father and his four children developed widened pupils, fits of laughter and delirium. The mushroom responsible could be identified a few years later from James Sowerby's Coloured Figures of English Fungi or Mushrooms (1803), where it appears under the name Agaricus glutinosus. The German mycologist Jochen Gartz judged that description fully compatible with the liberty cap.

The case is also the first recorded example of the problem this site keeps returning to: people picking small mushrooms in grass without knowing what they are.

Naming the species

Elias Magnus Fries described the species in 1838 as Agaricus semilanceatus. In those years almost every gilled mushroom was placed in the giant genus Agaricus. In 1871 the German mycologist Paul Kummer raised many of Fries's subdivisions to genera, and the liberty cap became Psilocybe semilanceata, the name it still has.

1963: psilocybin in a European mushroom

Psilocybin was first isolated from Mexican mushrooms by Albert Hofmann at Sandoz in 1958. In the early 1960s Hofmann analysed liberty caps collected in Switzerland and France by the French botanist Roger Heim and found about 0.25 percent psilocybin by dry weight. Their 1963 paper was the first report of psilocybin in a European species. Collections from Scotland and England confirmed it in the late 1960s, followed by Czechoslovakia, Germany, Norway, Belgium and Finland. The chemistry entry gives the later measurements.

The 1970s in Britain

In 1978 psychiatrists in the British Journal of Psychiatry described three patients who had eaten liberty caps, calling the use of this indigenous mushroom "a new fashion", and advised emergency doctors to ask about it (Hyde et al. 1978).

2005: the law catches up with the fresh mushroom

For decades British law controlled psilocybin and psilocin as chemicals, and the mushroom only once it had been prepared, for example dried. The fresh mushroom sat in a gap that the explanatory notes to the Drugs Act 2005 describe. Section 21 of that Act closed it from 18 July 2005: any fungus containing psilocin became Class A. Ireland followed on 31 January 2006, and the Netherlands placed psilocybin mushrooms, the liberty cap named among them, on List II of the Opium Act from 1 December 2008. The current position is set out in the law entry.

What to read next

The field characters entry describes the species as mycologists see it now, and lookalikes covers the species that continue to cause poisonings two centuries after Green Park.