Psilocybe silvatica is a psilocybin mushroom in the section Semilanceatae of the genus Psilocybe. Psilocybin is the main active compound. The species is closely related to its European twin Psilocybe medullosa, which differs genetically, and the American Psilocybe pelliculosa, which can be distinguished by spore size and cheilocystidia shape.
The fungus was first described by American mycologist Charles Horton Peck in 1889 as Psathyra silvatica. Rolf Singer and Alexander H. Smith transferred it to Psilocybe in 1958.