Psilocybe cyanescens, commonly known as the wavy cap or potent psilocybe, is a species of potent psychedelic mushroom. The main compounds responsible for its psychedelic effects are psilocybin and psilocin. It belongs to the family Hymenogastraceae. A formal description of the species was published by Elsie Wakefield in 1946 in the Transactions of the British Mycological Society, based on a specimen she had recently collected at Kew Gardens. She had begun collecting the species as early as 1910. The mushroom is not generally regarded as being physically dangerous to adults.

Psilocybe cyanescens can sometimes fruit in colossal quantities; more than 100,000 individual mushrooms were found growing in a single patch at a racetrack in England.

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