Psilocybe

''Psilocybe'' ( ) is a genus of gilled mushrooms, growing worldwide, in the family Hymenogastraceae. Most or nearly all species contain the psychedelic compounds psilocybin and psilocin.

Taxonomy

Taxonomic history

A 2002 study of the molecular phylogeny of the agarics 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 of the genus, ''Psilocybe '' (now Deconica montana), was in the non-bluing clade, but in 2010 the type species was changed to '' P. 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.

''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. 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''.

Modern classification

In 2007, a paper by Redhead ''et al.'' proposed conserving the genus ''Psilocybe'' with ''Psilocybe semilanceata'' as its type species. 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. 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). However, it has been demonstrated that '' P. fuscofulva'', a species that used to be known as ''P. atrobrunnea'', belongs to the genus ''Psilocybe'' s.s. but does not contain psychotropic compounds. Negative results have also been published for '' P. fimetaria''.

Etymology

The genus name ''Psilocybe'' is a compound of the Greek elements ψιλός (''psilós'') "bare" / "naked" and κύβη (''kúbe'') "head" / "swelling", 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.

Description

''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). 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.

Distribution and habitat

Geographically, species in this genus are found throughout the world in most biomes. The greatest species diversity seems to be in the neotropics, from Mesoamerica through Brazil and Chile. ''Psilocybe'' are found in a variety of habitats and substrates. Many of the species found in temperate regions, such as '' Psilocybe cyanescens'', seem to have an affinity for landscaped areas mulched with woodchips and are actually rather rare in natural settings removed from human habitation. Contrary to popular belief, only a minority of ''Psilocybe'' species, such as '' P. cubensis'' and '' P. subcubensis'', grow directly on feces. Many other species are found in habitats such as mossy, grassy, or forest humus soils.

Psychoactivity

Biochemistry and pharmacology

The psilocybin molecule is indirectly responsible for the hallucinogenic properties of the ''Psilocybe''. This compound, as well as all other indole alkaloids, are derived from the amino acid tryptophan, being the only amino acid with the indole-amine ring. Tryptophan is converted to tryptamine by decarboxylation. Two methylation steps occur producing DMT, another psychedelic compound. Hydroxylation of this compound produces the more potent hallucinogen psilocin, followed by phosphorylation yielding psilocybin. After ingestion of the psilocybin compound alkaline phosphatases present in the body's digestive system, kidneys, and possibly in the blood readily cleave the phosphoryl ester bond from psilocybin, yielding the hydroxyl compound, psilocin. Psilocin is the chemical primarily responsible for the hallucinogenic effects of the ''Psilocybe''. The blue-staining species of ''Psilocybe'' are characterized by the presence of psilocin and psilocybin. This blue-staining rea