Psilocybe (/ˌsaɪloʊˈsaɪbi/ SY-loh-SY-bee)[2] is a genus of gilled mushrooms, growing worldwide, in the family Hymenogastraceae. Most or nearly all species contain the psychedelic compounds Psilocybin, psilocin and baeocystin.
The genus name Psilocybe is a compound of the Greek elements ψιλός (psilós) "bare" / "naked" and κύβη (kúbe) "head" / "swelling",[3] giving the meaning "bare-headed" (i.e. bald) referring to the mushroom's detachable pellicle (loose skin over the cap), which can resemble a bald pate.
Psilocybe fruit bodies are typically small, nondescript mushrooms with a typical "little brown mushroom" morphology. Macroscopically, they are characterized by their small to occasionally medium size, brown to yellow-brown coloration, with a typically hygrophanous cap, and a spore print-color that ranges from lilac-brown to dark purple-brown (though rusty-brown colored varieties are known in at least one species).[4] Hallucinogenic species typically have a blue-staining reaction when the fruit body is bruised. Microscopically, they are characterized by pileipellis with hyphae that run parallel to the pileus surface, forming a cutis, by their lack of chrysocystidia, and by spores that are smooth, ellipsoid to rhomboid to subhexagonal in shape, with a distinct apical germ pore. Ecologically, all species of Psilocybe are saprotrophs, growing on various kinds of decaying organic matter.[5][6]
A 2002 study of the molecular phylogeny of the agarics[7] indicated that the genus Psilocybe as then defined was polyphyletic, falling into two distinct clades that are not directly related to each other. The blue-staining hallucinogenic species constituted one clade and the non-bluing species the other. The previous type species (Psilocybe montana) of the genus was in the non-bluing clade, but in 2010 the type species was changed to Psilocybe semilanceata, a member of the bluing clade. A 2006 molecular phylogenetic study of the Agaricales by Matheny and colleagues, further demonstrated the separation of the bluing and non-bluing clades of Psilocybe in a larger, strongly supported phylogenetic tree of the Agaricales.[8]
Psilocybe had been placed taxonomically in the agaric family Strophariaceae based upon its spore and pileipellis morphology. The phylogenetic study by Matheny et al., placed the non-bluing Psilocybe and its close relatives in a basal position within the Strophariaceae, a sister taxon to a clade containing the other genera within that family. The bluing Psilocybe, however, form a clade that is sister to Galerina in the newly revised family, Hymenogastraceae that used to be restricted to secotioid, false-truffles.[8] The phylogenetic study by Moncalvo, et al. confirmed that the agaric genus Melanotus is simply a subgroup of the non-bluing Psilocybe, all of which are placed in Deconica, and also pointed to a close relationship between the latter genus and the genera Kuehneromyces and Phaeogalera.[7]
In 2007, a paper by Redhead et al. proposed conserving the genus Psilocybe with Psilocybe semilanceata as its type species.[9] The suggestion was accepted by unanimous vote of the Nomenclature Committee for Fungi of the International Botanical Congress in 2010, meaning that P. semilanceata (a member of the bluing clade) now serves as the type species of the genus.[10] Since P. semilanceata is now the type species of the genus, the bluing hallucinogenic clade remained in the genus Psilocybe (Hymenogastraceae) while the non-bluing clade were transferred to the genus Deconica (Strophariaceae).[11] However, it has been demonstrated that Psilocybe fuscofulva, a species that used to be known as Psilocybe atrobrunnea, belongs to the genus Psilocybe s.s. but does not contain psychotropic compounds.[12]