 Amanita muscaria , commonly known as the fly agaric or fly <unk> , is a mushroom and psychoactive <unk> 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 and birch plantations , and is now a true cosmopolitan species . It associates with various deciduous and coniferous trees . 
