Agaricus bitorquis

Cap

4-18(25) cm in diam., convex then broadly convex to spreading, slightly depressed in center or raised, dry, smooth, suede-like to slightly laciniated or sometimes scaly, whitish to ivory, fading to buff, greyish, dark brownish to tan with age, often encrusted with earth, margin long strongly involute at first, often extending beyond the blades

Gills

free, narrow, up to 10 mm wide, close together, pinkish at first, soon greyish-pink, then dark reddish-brown to dark brown, blackish-brown at the end, with edges paler than the faces

Stem

2-6(10) x 1-3(4) cm, equal, slightly broadened towards base to subbulb, often tapering or pointed at base, very firm, full, smooth, whitish

Partial veil

membranous, thick, leaving ± median or sometimes basal ring on stipe, prominent, sheathing, persistent, complex, double, not toothed, whitish, with spreading, thicker upper layer and narrowly banded lower layer

Flesh

thick, 10-30 mm, firm to hard, whitish, blushing slowly and slightly at the base of the foot when cut

Smell and flavor

pleasant, sweet, fungal to sweet odor and pleasant, sweet, nutty flavor

Spore

dark brown

Basidia

cylindrical-clavate, mostly with 4 sterigmata 2-3 µm long, sometimes 2, uncurled at base, 19-30 x 6-8.5 µm

Spores

broadly ellipsoid to ellipsoid, smooth, thickened wall, without distinct germ pore and with inconspicuous hilar appendage, dark brown, (4.5)5.8-6(8.3) x (4.1)4.5- 5.1(6) µm, 5.9 X 4.8 µm average

Cheilocystidia

numerous, cylindrical to cylindrical-keyed, continuous, 19-30 x 6-7.5 µm

Pleurocystidia

absent

Pileipellis

in cutis
formed of appressed, parallel, uncurled hyphae, partly pigmented brown, 4-8 µm in diameter

Lamellar edge

sterile

Mode of growth

solitary, scattered or gregarious

Ecology

saprotrophic on compacted and trampled soils in open and urban environments, playgrounds, sidewalks and paths, often buried, even emerging through the cracked asphalt that it raises

Period

May to October, in cool weather

Frequency

occasional

Edibility

choice edible 

Chemical reactions

negative to KOH on the cap

Remarks

This agaric is characterized by its large size, its stocky stature, its whitish cap at the beginning, suede, with a strongly rolled margin, its double ring, sheathing and in padding, its firm flesh, blushing slowly and slightly at the base of the foot, its sweet smell, its dark chocolate brown spores and its preferential growth on compacted soil in open areas.
Since it emerges little from the ground, it often goes unnoticed.
It is surprisingly hardy and can sometimes be seen in driveways, pushing through asphalt, much to the surprise of harvesters and homeowners.
A. bernardii differs in its cap covered with large scales, its flesh becoming more reddish when cut, its briny odor, its convoluted cylindrical cheilocystidia and its growth in sandy, disturbed, grassy or saline environments.
A. aff. campestris has really pink gills at first, a single, thin, delicate ring, and larger spores, 6.5-8.5 x 4.5-5.5 µm.