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Members of Agaricus are characterized by having a fleshy cap or pileus, from the underside of which grow a number of radiating plates or gills on which are produced the naked spores. They are distinguished from other members of their family, Agaricaceae, by their chocolate-brown spores. Members of Agaricus also have a stem or stipe, which elevates the pileus above the object on which the mushroom grows, and a partial veil, which protects the developing gills and later forms a ring or annulus on the stalk.
For many years members of the genus Agaricus were given the generic name Psalliota, and this can still be seen in older books on mushrooms. All proposals to conserve Agaricus against Psalliota or vice versa have so far been considered superfluous.
Several origins of Agaricus have been proposed; It possibly derives "from Agarica of Sarmatica, a district of Russia" (!). Note also Greek ??a???[3]?? "a sort of tree fungus" (There's been an Agaricon Adans. genus, treated by Donk in Persoonia 1180)
