Agaricus

Agaricus is a large and important genus of mushrooms containing both edible and poisonous species, with possibly over 300 members worldwide. The genus includes the common ("button") mushroom (Agaricus bisporus), and the Field mushroom (Agaricus campestris) the dominant cultivated mushrooms of the West.

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.

Taxonomy
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 ἀ γαρικ όν "a sort of tree fungus" (There's been an Agaricon Adans. genus, treated by Donk in Persoonia 1:180)

Donk reports Linnaeus' name is devalidated (so that the proper author citation apparently is "L. per Fr., 1821") because Agaricus was not linked to Tournefort's name (Linnaeus places both Agaricus Dill. and Amanita Dill. in synonymy), but truly a replacement for Amanita Dill., which would require that A. quercinus, not A. campestris be the type. This question compounded by the fact that Fries himself used Agaricus roughly in Linnaeus' sense (which leads to issues with Amanita), and that A. campestris was eventually excluded from Agaricus by Karsten and was apparently in Lepiota at the time Donk wrote this, commenting that a type conservation might become necessary.

The alternate name for the genus, Psalliota, derived from the Greek ''psalion/ψάλιον, "ring", was first published by Fries (1821) as trib. Psalliota. The type is Agaricus campestris (widely accepted, except by Earle, who proposed A. cretaceus). Paul Kummer (not Quélet, who merely excluded Stropharia) was the first to elevate the tribe to a genus. Psalliota was the tribe containing the type of Agaricus, so when separated, it should have caused the rest of the genus to be renamed, not what happened. It seems to be currently not considered valid, or a junior homotypic synonym, anyway the explanation is that it was raised by (in retrospect) erroneously maintaining the tribe name.

List of species

 * Agaricus abruptibulbus
 * Agaricus aestivalis
 * Agaricus aestivalis var. Veneris
 * Agaricus aff. benesii
 * Agaricus altipes
 * Agaricus arcticus
 * Agaricus arvensis (Horse mushroom)
 * Agaricus arvensis var. exquisita
 * Agaricus arvensis var. macrolepis
 * Agaricus arvensis var. exquisita
 * Agaricus augustus (The Prince)
 * Agaricus benesii
 * Agaricus bernardii
 * Agaricus bisporus (Cultivated mushroom)
 * Agaricus bisporus var. albidus
 * Agaricus bisporus var. hortensis
 * Agaricus bitorquis
 * Agaricus bohusii
 * Agaricus bresadolianus
 * Agaricus campestris (Field mushroom/Meadow mushroom (US))
 * Agaricus cellaris
 * Agaricus cf. pseudopratensis
 * Agaricus comtulus
 * Agaricus cupreobrunneus
 * Agaricus devoniensis
 * Agaricus dulcidulus
 * Agaricus essettei
 * Agaricus excellens
 * Agaricus fissuratus
 * Agaricus freirei
 * Agaricus fuscofibrillosus
 * Agaricus geesterani syn. Allopsalliota geesterani
 * Agaricus haemorrhoidarius
 * Agaricus hortensis
 * Agaricus impudicus
 * Agaricus koelerionensis
 * Agaricus lacrymabunda
 * Agaricus langei
 * Agaricus lanipes
 * Agaricus laskibarii
 * Agaricus leucotrichus
 * Agaricus lilaceps (Cypress Agaricus)
 * Agaricus litoralis
 * Agaricus luteomaculatus
 * Agaricus macrocarpus
 * Agaricus macrosporus
 * Agaricus maleolens
 * Agaricus medio-fuscus
 * Agaricus menieri
 * Agaricus moelleri (Inky Mushroom)
 * Agaricus niveolutescens
 * Agaricus nivescens
 * Agaricus osecanus
 * Agaricus pampeanus
 * Agaricus perrarus
 * Agaricus pilatianus
 * Agaricus praeclaresquamosus syn. Agaricus placomyces
 * Agaricus praeclaresquamosus var. griseus
 * Agaricus praeclaresquamosus var. meleagris
 * Agaricus praeclaresquamosus var. terricolor
 * Agaricus porphyrizon
 * Agaricus porphyrocephalus
 * Agaricus praeclaresquamosus
 * Agaricus purpurellus
 * Agaricus radicatus
 * Agaricus romagnesii
 * Agaricus rotalis
 * Agaricus rufotegulis
 * Agaricus semotus
 * Agaricus silvaticus
 * Agaricus silvaticus var. pallidus
 * Agaricus silvicola (Wood Mushroom)
 * Agaricus spissicaulis
 * Agaricus stramineus
 * Agaricus subfloccosus
 * Agaricus subperonatus
 * Agaricus subrufescens (= Agaricus blazei)
 * Agaricus subrutilescens (Wine-Colored Agaricus)
 * Agaricus urinascens
 * Agaricus urinascens var. excellens
 * Agaricus vaporarius
 * Agaricus variegans
 * Agaricus xanthodermus (Yellow staining mushroom)
 * Agaricus xanthodermus var. griseus
 * Agaricus xanthodermus var. lepiotoides
 * Agaricus xanthodermus var. meleagris

Uses
Agaricus is used in homeopathy for twitching and spasms and for back pain markedly worse from sitting.