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Psilocybe is a genus of small mushrooms growing worldwide. This genus is best known for its species with 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 ψιλος + κυβη and literally means "bare headed", referring to the mushroom's plain cap. It may be pronounced with the accent on the first syllable (IPA [ˈsɪləˌsaɪbi]; MWCD [ˈsi-lə-ˌsī-bē]) or the second (IPA [saɪˈlɒsəbi]; MWCD [sī-ˈlä-sə-bē]). 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.
Psilocybe fruiting bodies are typically small, non-descript 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 pileus, 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 fruiting 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. 
A recent 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 type species (Psilocybe montana) is in the non-bluing clade.
Psilocybe is placed taxonomically in the agaric family Strophariaceae based upon its spore and pileipellis morphology. However, molecular studies indicate that the Strophariaceae may be a polyphyletic grouping of several clades that are fairly close to each other, but not necessarily sister taxa, hence, the precise relationship of Psilocybe to other agaric genera awaits further study. 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.
Distribution and habitat
Geographically, species in this genus are found throughout the world in most biomes, with the exception of high deserts. 60 species of Psilocybe occur in the United States, of which 25 are hallucinogenic.  For the bluing Psilocybe, 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 bluing 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. coprophila and P. cubensis, grow directly on dung. Many other species are found in habitats such as mossy, grassy, or forest humus soils.
Biochemistry and pharmacology
The blue-staining species of Psilocybe are characterized by the presence of psilocin and psilocybin. The blue-staining reaction, while not completely understood, is thought to be a caused by a degradation reaction of psilocin, hence the degree of bluing in a Psilocybe fruiting body correlates directly with the concentration of psilocin in the mushroom. Psilocybin is chemically far more stable than psilocin, the latter compound being largely lost when the mushroom is heated or dried.
(See Psilocybin for a more in-depth discussion of the pharmacology of psilocybin and psilocin.)
Medical and psychiatric aspects
Among some groups of Mesoamerican natives, hallucinogenic Psilocybe have been used by native healers for centuries for divining the causes of illness and as part of psychological counseling. Contemporary researchers have generally preferred to use purified psilocybin in medical and psychiatric research, though in practice, whole Psilocybe cubensis is often used.
For details on contemporary research, see: Psilocybin: Medicine.
History and ethnography
Hallucinogenic species of Psilocybe have a long history of use among the native peoples of Mesoamerica for religious communion, divination, and healing, from pre-Columbian times up to the present day. Hallucinogenic Psilocybe were known to the Mexicans as teonanácatl (literally "god mushroom") and were reportedly served at the coronation of Moctezuma II in 1502. After the Spanish conquest, the use of hallucinogenic plants and mushrooms, like other pre-Christian traditions, was forcibly suppressed and driven underground.
By the twentieth century, hallucinogenic mushroom use was thought by non-Indians to have disappeared entirely. However, in 1955, Valentina and R. Gordon Wasson became the first Westerners to actively participate in an indigenous mushroom ceremony. The Wassons did much to publicize their discovery, even publishing an article on their experiences in Life in 1957. In 1956, Roger Heim identified the hallucinogenic mushroom that the Wassons had brought back from Mexico as Psilocybe and in 1958, Albert Hofmann first identified psilocin and psilocybin as the active compound in these mushrooms.
The popularization of entheogens by Wasson, Timothy Leary, and others has led to an explosion in the use of hallucinogenic Psilocybe throughout the world. By the early 1970s, a number of psychoactive Psilocybe species were described from temperate North America, Europe, and Asia and were widely collected. Books describing methods of cultivating Psilocybe cubensis in large quantities were also published. The relatively easy availability of hallucinogenic Psilocybe from wild and cultivated sources has made it among the most widely used of the hallucinogenic drugs.
Psilocybin and psilocin are listed as Schedule I drugs under the United Nations 1971 Convention on Psychotropic Substances. Schedule I drugs are drugs with a high potential for abuse that have no recognized medical uses. This status is reflected in the drug laws of the majority of the world's nations. Possession and use of psilocybin mushrooms, including the bluing species of Psilocybe, is therefore prohibited by extension. However, in many national, state, and provincial drug laws, there is a great deal of ambiguity about the legal status of psilocybin mushrooms, as well as a strong element of selective enforcement in some places. The legal status of Psilocybe spores is even more ambiguous, as the spores contain neither psilocybin nor psilocin, and hence are not illegal to sell or possess in many jurisdictions, though many jurisdictions will prosecute under broader laws prohibiting items that are used in drug manufacture. A few jurisdictions (such as the US states of California, Georgia, and Idaho) have specifically prohibited the sale and possession of psilocybin mushroom spores. Cultivation of psilocybin mushrooms is considered drug manufacture in most jurisdictions and is often severely penalized, though some countries and one US state have ruled that growing psilocybin mushrooms does not qualify as "manufacturing" a controlled substance.
- Psilocybe cubensis, (= Stropharia cubensis); the most commonly grown and consumed Psilocybe, due to ease of cultivation and large size of carpophores; also commonly collected throughout the tropics and subtropics, including the US Gulf Coast; nicknamed the commercial psilocybe.
- Psilocybe semilanceata, found in northern temperate climates; nicknamed the liberty cap.
- Psilocybe cyanescens, native to the Pacific Northwest of North America, but also found in western Europe; nicknamed the wavy-cap or wavies.
- Psilocybe azurescens, a highly potent species native to Oregon, but popular in outdoor cultivation, and expanding its range as a result; nicknamed azies.
- Paye Y. (2003). Genesis of the PF Redspore psilocybe. Erowid.org (website).
- Guzmán G. (1983). The Genus Psilocybe: a systematic revision of the known species including the history, distribution and chemistry of the hallucinogenic species. (Beihefte zur Nova Hedwigia 74.) Vaduz, LI: J. Cramer. [out of print] ISBN 3-7682-5474-7
- Largent DL and Baroni TJ. (1988). How to identify mushrooms to genus VI: modern genera. Eureka, CA: Mad River Press. ISBN 0-916-422-76-3
- Moncalvo JM, et al. 2002. One hundred and seventeen clades of euagarics. Molecular Phylogenetics and Evolution 23:357-400. Available from: http://www.botany.utoronto.ca/faculty/moncalvo/117clade.pdf
- Wasson RG (1957). "Seeking the magic mushroom". Life (June 10). article reproduced online
- Furst, Peter T. 1976. Hallucinogens and Culture. San Francisco: Chandler and Sharp Publishers. Chapter Seven, The sacred mushrooms: Rediscovery in Mexico; pp 75-88. Available from: http://www.sunrisedancer.com/radicalreader/detail.asp?iArt=4&iType=21 ISBN 0-88316-517-1
- Metzner, Ralph (ed). 2005. Sacred Mushroom of Visions: Teonanácatl [2nd ed]. Rochester, VT: Park Street Press. 304 pp. ISBN 1-59477-044-1
- Ott, Jonathan and Bigwood, Jeremy.1978. Teonanácatl: Hallucinogenic mushrooms of North America. Seattle: Madrona Publishers. 175 p. [out of print] ISBN 0-914842-32-3
- Stamets, Paul. 1996. Psilocybin Mushrooms of the World. Berkeley: Ten Speed Press. 245 pp. ISBN 0-89815-839-7
- Erowid - Psilocybin Mushrooms
- Erowid Psilocybe Mushroom FAQ
- Visionary Mushrooms
- Zauberpilz.com Comprehensive Magic Mushroom Information Source & Forums
- MushroomExpert.com Taxonomy in Transition: The Strophariaceae - Taxonomic issues of Psilocybe and other stropharioid fungi.
- Machiel E. Noordeloos: Psilocybe - taxonomy and characteristics of non-bluing Psilocybe.
History and ethnography
- The Ones that Stain Blue
- The Sacred Mushroom Teonanácatl - Chapter from "LSD: My Problem Child" by Albert Hofmann
- Timeline of mushroom use at Erowid.org
- Erowid - Psilocybin Mushrooms: Legal Status
- EMCDDA Thematic Paper: Hallucinogenic mushrooms - an emerging trend case study , June 26 2006
- Visionary Mushrooms Psychedelic mushrooms.
- The Shroomery Detailed information about psilocybe mushrooms including identification, cultivation and spores, psychedelic images, trip reports, a dosage calculator and an active community.
- Mycotopia Interactive Global community devoted to all things mushroom.
- Mushroom John's Shroom World 13,000 Images of Shrooms and related items, dozens of articles, books, and art.
- Psilocybe mushrooms from The Encyclopedia of Psychoactive Substances
- INCHEM - Psilocybe and others - Toxicology of psilocybin mushrooms.
- A Worldwide Geographical Distribution of the Neurotropic Fungi