WEBMar 26, 2024 · The fly agaric (Amanita muscaria) is a poisonous fungus. fungus, any of about 144,000 known species of organisms of the kingdom Fungi, which includes the yeasts, rusts, smuts, mildews, molds, and mushrooms. There are also many funguslike organisms, including slime molds and oomycetes (water molds), that do not belong to kingdom Fungi but are ...