Common Name: torq
Cap 5-15 cm broad, convex, becoming broadly so in age, sometimes expanding to plane with an upturned margin; surface smooth, whitish, often with adhering dirt; flesh white, thick, firm, unchanging; odor and taste mild.
Gills free, close, pallid, becoming pale brown, blackish-brown at maturity.
Stipe 4-10 cm long, 2-4 cm thick, stout, equal to enlarged below, solid; surface whitish, more or less smooth, sometimes with fine, appressed scales at the apex; veil membranous, thick, white, sheathing from the base of the stipe.
Spores 5-6.5 x 4-5.5 µm, smooth, elliptical; spore print chocolate brown.
Scattered to gregarious in disturbed habitats, e.g. roadsides, paths, vacant lots etc., preferring heavy soils like those surrounding San Francisco Bay; fruiting from mid to late winter.
Excellent; substantial size, firm texture, and good flavor make this one of the best Agaricus species for the table.
Agaricus bitorquis is recognized by a usually short, compact, stature, smooth, white, but frequently dirty cap, and partially emergent fruitings, i.e. often just breaking through the soil surface. It is most likely to be confused with A. bernardii, which is also white and similar in stature, but the latter has a distinct briny odor and the flesh turns pink when cut.