Psilocybe semilanceata, commonly known as the liberty cap, is a species of fungus which produces psilocybin, psilocin and baeocystin. It is one of the most widely distributed psilocybin mushrooms in nature. The mushrooms have a distinctive conical to bell-shaped cap, up to 2.5 cm (1 in) in diameter, with a small nipple-like protrusion on the top. They are yellow to brown, covered with radial grooves when moist, and fade to a lighter color as they mature. Their stipes tend to be slender and long, and the same color or slightly lighter than the cap. The gill attachment to the stipe is adnexed (narrowly attached), and they are initially cream-colored before tinting purple to black as the spores mature. The spores are dark purplish-brown en masse, ellipsoid in shape, and measure 10.5–15 by 6.5–8.5 μm. The mushroom grows in grassland habitats, especially wetter areas. Unlike P. cubensis, the fungus does not grow directly on dung; rather, it is a saprobic species that feeds off decaying grass roots. It is widely distributed in the temperate areas of the Northern Hemisphere, particularly in Europe, and has been reported occasionally in temperate areas of the Southern Hemisphere as well. The earliest reliable history of P. semilanceata intoxication dates back to 1799 in London, and in the 1960s the mushroom was the first European species confirmed to contain psilocybin. The possession or sale of psilocybin mushrooms is illegal in many countries.
Taxonomy
The species was first described by Elias Magnus Fries as Agaricus semilanceatus in his 1838 work Epicrisis Systematis Mycologici. Paul Kummer transferred it to Psilocybe in 1871 when he raised many of Fries's sub-groupings of Agaricus to the level of genus. Panaeolus semilanceatus, named by Jakob Emanuel Lange in both 1936 and 1939 publications, is a synonym. According to the taxonomical database MycoBank, several taxa once considered varieties of P. semilanceata to be synonymous with the species now known as Psilocybe strictipes: the caerulescens variety described by Pier Andrea Saccardo in 1887 (originally named Agaricus semilanceatus var. coerulescens by Mordecai Cubitt Cooke in 1881), the microspora variety described by Rolf Singer in 1969, and the obtusata variety described by Marcel Bon in 1985. Several molecular studies published in the 2000s demonstrated that Psilocybe, as it was defined then, was polyphyletic. The studies supported the idea of dividing the genus into two clades, one consisting of the bluing, hallucinogenic species in the family Hymenogastraceae, and the other the non-bluing, non-hallucinogenic species in the family Strophariaceae. However, the generally accepted lectotype (a specimen later selected when the original author of a taxon name did not designate a type) of the genus as a whole was Psilocybe montana, which is a non-bluing, non-hallucinogenic species. If the non-bluing, non-hallucinogenic species in the study were to be segregated, it would have left the hallucinogenic clade without a valid name. To resolve this dilemma, several mycologists proposed in a 2005 publication to conserve the name Psilocybe, with P. semilanceata as the type. As they explained, conserving the name Psilocybe in this way would prevent nomenclatural changes to a well-known group of fungi, many species of which are "linked to archaeology, anthropology, religion, alternate life styles, forensic science, law enforcement, laws and regulation". Further, the name P. semilanceata had historically been accepted as the lectotype by many authors in the period 1938–68. The proposal to conserve the name Psilocybe, with P. semilanceata as the type was accepted unanimously by the Nomenclature Committee for Fungi in 2009. The mushroom takes its common name from the Phrygian cap, also known as the "liberty cap", which it resembles; P. semilanceata shares its common name with P. pelliculosa, a species from which it is more or less indistinguishable in appearance. The Latin word for Phrygian cap is pileus, nowadays the technical name for what is commonly known as the "cap" of a fungal fruit body. In the 18th century, Phrygian caps were placed on Liberty poles, which resemble the stipe of the mushroom. The generic name is derived from Ancient Greek psilos (ψιλός) 'smooth, bare' and Byzantine Greek kubê (κύβη) 'head'. The specific epithet comes from Latin semi 'half, somewhat' and lanceata, from lanceolatus 'spear-shaped'.
Description
The cap of P. semilanceata is 5–25 mm (0.20–0.98 in) in diameter and 6–22 mm (0.24–0.87 in) tall. It varies in shape from sharply conical to bell-shaped, often with a prominent papilla (a nipple-shaped structure), and does not change shape considerably as it ages. The cap margin is initially rolled inward but unrolls to become straight or even curled upwards in maturity. The cap is hygrophanous, meaning it assumes different colors depending on its state of hydration. When it is moist, the cap is ochraceous to pale brown to dark chestnut brown, but darker in the center, often with a greenish-blue tinge. When moist, radial grooves (striations) can be seen on the cap that correspond to the positions of the gills underneath. When the cap is dry, it becomes much paler, a light yellow-brown color. Moist mushrooms have sticky surfaces that result from a thin gelatinous film called a pellicle. This film becomes apparent if a piece of the cap is broken by bending it back and peeling away the piece. When the cap dries from exposure to the sun, the film turns whitish and is no longer peelable. On the underside of the mushroom's cap, there are between 15 and 27 individual narrow gills that are moderately crowded together, and they have a narrowly adnexed to almost free attachment to the stipe. Their color is initially pale brown, but becomes dark gray to purple-brown with a lighter edge as the spores mature. The slender yellowish-brown stipe is 4.5–14 cm (1.8–5.5 in) long by 1–3.5 mm (0.04–0.14 in) thick, and usually slightly thicker towards the base. The mushroom has a thin cobweb-like partial veil that does not last long before disappearing; sometimes, the partial veil leaves an annular zone on the stipe that may be darkened by spores. The flesh is thin and membrane-like, and roughly the same color as the surface tissue. It has a farinaceous (similar to freshly ground flour) odor and taste. All parts of the mushroom will stain a bluish color if handled or bruised, and it may naturally turn blue with age.
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