How to tell Salty mushroom from Yellow stainer

The cap is 6–15 cm across and very fleshy. Young caps are hemispherical, then convex and flattened, and the margin stays inrolled for a long time.

The skin is white, cream or greyish, dry and smooth at first, often with brownish spots. With age it cracks into coarse brownish scales and furrows, so the cap looks like cracked earth. Mushrooms often come up already dirty, with sand or soil on the cap.

Cap 5-15 cm across; in young mushrooms firmly hemispherical to squared-off (a telltale feature: the "square" young cap), later convex to flat. White to cream, sometimes greyish-brown in the centre. Its most characteristic sign: touching the cap or its margin leaves bright chrome-yellow marks, especially noticeable on young mushrooms. The surface is smooth and slightly sticky in wet weather.

The gills are free, meaning they don't reach the stem, and very crowded. In young mushrooms they are greyish pink or pink, then reddish brown, and chocolate in mature ones. They are never white in a mature Agaricus.

The spore print is chocolate brown. A white print means it isn't an Agaricus.

Gills free and crowded: pale pinkish-grey when young, turning dark brown to chocolate-black with age. Spore print dark brown. This gill colour is typical of Agaricus, so it won’t help you tell the yellow stainer apart.

The stem is 4–10 cm tall and 2–4 cm thick, white, firm and solid. It's usually shorter than the cap is wide, which makes the mushroom look squat.

There is a single narrow, sleeve-like ring with an upturned edge; in young mushrooms it is thick and rubbery. There is no sac (volva) at the base. The base often sits deep in the soil, so dig the mushroom up whole to check it.

Stem 5-12 cm tall and 1-2 cm thick, cylindrical, with a pronounced bulbous base (other Agaricus species have more even stems). White. The most important diagnostic sign: cut it, and 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). Higher up there’s a white membranous ring, distinct in young mushrooms.

The flesh is thick, firm and white. When cut or pressed it reddens, turning orange-red or reddish brown, sometimes vividly, sometimes slowly and only faintly. It never turns yellow. The taste is mild, slightly salty according to some.

Flesh firm and white in the cap and upper stem, turning bright yellow at the base of the stem the moment it’s cut. THE BASE OF THE STEM TURNS BRIGHT CHROME YELLOW WHEN CUT, and that’s the main diagnostic sign. The cap yellows too, but more weakly. The smell is distinct and unpleasant: ink, phenol, medicinal ointment, creosote.

Descriptions of the smell vary: briny, fishy, unpleasant, and some authors also notice a hint of aniseed. That is where its German and French names meaning smelly mushroom come from. Treat the smell as a hint only: the reddening flesh, the pink to chocolate gills and the single ring decide. A strong smell of ink or carbolic points to the poisonous yellow stainer.

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. The smell is very telling, but it can be faint in a raw mushroom, and then the bright yellow cut stem base decides it. No edible Agaricus smells like this, and cooking only makes the smell stronger.