Amanita muscaria, commonly known as the fly agaric or fly Amanita is a poisonous and psychoactive basidiomycete fungus, one of many in the genus Amanita. Native throughout the temperate and boreal regions of the Northern Hemisphere, Amanita muscaria has been unintentionally introduced to many countries in the Southern Hemisphere, generally as a symbiont with pine plantations, and is now a true cosmopolitan species. It associates with various deciduous and coniferous trees. The quintessential toadstool, it is a large white-gilled, white-spotted, usually deep red mushroom, one of the most recognizable and widely encountered in popular culture.
A large conspicuous mushroom, Amanita muscaria is generally common and numerous where it grows, and is often found in groups with basidiocarps in all stages of development. Fully grown, the bright red cap is usually around 8-20 cm in diameter, though larger specimens have been found. The red colour may fade after rain and in older mushrooms. After emerging from the ground, the cap is covered with numerous small white to yellow flecks (warts) which are remnants of the universal veil, a membrane that encloses the entire mushroom when it is still very young. The gills are white, as is the spore print. The stem is white, 5-20 cm high, with a basal bulb that bears universal veil remnants (more or less distinct rings or ruffs), and has the slightly brittle, fibrous texture typical of many large mushrooms. Between the basal universal veil remnants and gills are remnants of the partial veil, which covers the gills during development, in the form of a white ring. It can be quite wide and flaccid with age. There is generally no associated smell other than a mild earthiness.
Although generally considered poisonous, Amanita muscaria is otherwise famed for its hallucinogenic properties with its main psychoactive constituent being the compound muscimol. Used as an intoxicant by the Koryaks of the Kamchatka Krai of eastern Siberia, the mushroom has had a religious significance in Siberian culture and possibly also in ancient Scandinavian culture. The American banker and amateur ethnomycologist R. Gordon Wasson proposed the fly agaric was in fact the Soma talked about in the ancient Rig Veda texts of India; although this theory has been refuted by anthropologists, it gained common credence when first published in 1968.
The common name in English is thought to have been derived from its European use as an insecticide, sprinkled in milk. The fly-killing agent is now known to be ibotenic acid. Another compound isolated from the fungus is 1,3-diolein which is an insect attractor. An alternative derivation proposes that the term fly- refers not to insects as such but rather the delirium resulting from consumption of the fungus. This is based on the medieval belief that flies could enter a person's head and cause mental illness.
Amanita muscaria is the type species of the genus Amanita. By extension, it is also the type species of Amanita subgenus Amanita, as well as section Amanita within this subgenus. Amanita subgenus Amanita includes all Amanita with inamyloid spores. Amanita section Amanita includes those species with patchy universal veil remnants, including a volva that is reduced to a series of concentric rings and the veil remnants on the pileus being a series of patches or warts. Most species in this group also have a bulbous base.[
