Psilocybe: Description and Classification

Psilocybe is a genus of small mushrooms growing worldwide. This genus is best known for its species with psychedelic or hallucinogenic properties, widely known as "magic mushrooms", though the majority of species do not contain hallucinogenic compounds. Psilocin and psilocybin are the hallucinogenic compounds responsible for the psychoactive effects of many species in the genus. The word Psilocybe comes from the Greek words ψιλός + κύβη, and literally means "bare headed", referring to the mushroom's detachable pellicle (loose skin over the cap). It may be pronounced with the accent on the first syllable or the second. The final e is not silent. The marked difference between the Botanical Latin-based pronunciation (given here) and anglicized colloquial pronunciations (with a silent "e") is sometimes a source of confusion in oral communication about this genus.

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 cutis-type pileipellis, lack of chrysocystidia, and 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.

Classification

 A 2002 study of the molecular phylogeny of the agarics by Moncalvo, et al., indicates that the genus Psilocybe as presently defined is polyphyletic, falling into two distinct clades that are not directly related to each other. The blue-staining hallucinogenic species constitute one clade and the non-bluing species constitute the other. The previous type species (Psilocybe montana) of the genera 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, et al., further demonstrates the separation of the bluing and non-bluing clades of Psilocybe in a larger, strongly supported phylogenetic tree of the Agaricales. Psilocybe is placed taxonomically in the agaric family Strophariaceae based upon its spore and pileipellis morphology. The phylogenetic study by Matheny, et al., places 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-erected family, Hymenogastraceae. The phylogenetic study by Moncalvo, et al. has confirmed that the agaric genus Melanotus is simply a subgroup of the non-bluing Psilocybe, and also points to a close relationship between the latter group and the genera Kuehneromyces and Phaeogalera. 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 Psilocybe semilanceata (a member of the bluing clade) now serves as the type species of the genus. Since Psilocybe semilanceata is now the type species of the genus, the bluing hallucinogenic clade will remain in the genus Psilocybe while the non-bluing clade will likely be transferred to the genus Deconica.