How to tell Agaricus comtulus from Yellow stainer

Cap 5-15 cm across; in young mushrooms firmly hemispherical to squared-off (a characteristic feature — the "square" young cap), later becoming convex to flat. Color white to cream, sometimes grayish-brown in the center. The most characteristic sign — touching the cap or its margin leaves bright chrome-yellow spots, especially noticeable in young mushrooms. The surface is smooth, slightly sticky in wet weather.

The cap of Agaricus comtulus is small — 2 to 5 centimeters across. When young it is hemispherical or convex; with age it opens out flat. The surface is dry, smooth or finely fibrous, white, cream or with a faint grayish-yellowish tint, often darker in the center. It may turn faintly yellow when touched. Its small size and pale coloring give the mushroom a modest, delicate look.

Gilled hymenophore — gills free, crowded. When young — pale pinkish-gray, becoming with age dark brown, chocolate-blackish. Spore print dark brown. The gill color is typical of Agaricus — it doesn't help tell the yellow stainer apart.

The spore-bearing surface is made of gills. The gills are free, not attached to the stem, and crowded. Their color changes with age: in young mushrooms they are pale pink or grayish-pink, then darken to brown and blackish-brown. The spore print is dark brown. Pinkish young gills set Agaricus apart from the white-gilled poisonous amanitas.

Stem 5-12 cm tall, 1-2 cm thick, cylindrical, with a pronounced bulbous base (a difference from other Agaricus species, whose stems are more even). Color white. The most important diagnostic sign: when cut, the flesh at the base of the stem and in the bulb is bright chrome yellow, often almost neon, and the reaction is fast (10-30 seconds). On the upper part — a white membranous ring, distinct in young mushrooms.

The stem is thin, slender, white, 2 to 5 centimeters tall, often with a slightly thickened base. Near the top there is a thin whitish ring — a remnant of the veil — which can be fragile in small mushrooms. There is no volva at the base — an important difference from poisonous amanitas.

Flesh firm, white in the cap and upper stem, bright yellow at the base of the stem even when undamaged. When cut, THE BASE OF THE STEM TURNS BRIGHT CHROME YELLOW — the main diagnostic sign. The cap yellows too, but more weakly. The smell is distinct and unpleasant — ink, phenol, medicinal ointment, creosote.

The flesh is white and thin, and turns faintly yellow or stays unchanged when cut. The taste is mild and pleasant, with a light anise-almond note. Because the flesh is thin and the mushroom small, its culinary value is modest, so it rounds out a basket rather than forming the basis of a dish.

Distinct and unpleasant, with notes of ink, phenol, medicinal ointment, creosote, printer's ink. It comes out when you rub the flesh between your fingers, especially at the base of the stem. This smell is the most reliable sign: no edible Agaricus smells like this.

The smell is pleasant and faint, with an anise or almond note. If the mushroom smells of ink or carbolic and the flesh turns bright yellow when cut, it may be the poisonous yellow stainer or one of its small relatives, and you must not take it.