How to tell Soapy knight from White knight

The cap is 5-12 cm across, convex with an inrolled margin when young, becoming flattened and spreading with a small bump with age. The skin is smooth, slightly slimy in wet weather and dry and matte in dry weather. The colour is very variable: grey-white, olive-grey, greenish-grey, brownish-grey, and in some forms almost black in the centre. Old caps develop small cracks.

The cap is 4–10 cm across. Young caps are conical to convex with an inrolled margin, then flatten out around a small, low boss, often with a wavy edge. In the white knight the margin is smooth; a ribbed margin points more to the chemical knight of birch woods.

The colour is white to cream, sometimes with a pale yellow tinge. With age the centre turns ochre or yellowish brown, and old caps develop ochre spots. The surface is dry, matt and smooth, and stays dry even in rain.

The gills are notched (sinuate) where they meet the stem, moderately crowded and fleshy. They start out whitish and become creamy-greyish with age, often turning pink when damaged. The spore print is white.

The gills are white, later pale yellowish, thick, fairly distant and of unequal length. They are clearly notched just before the stem, and their edges are finely toothed.

The spore print is white. Pink or chocolate-brown gills mean a field mushroom relative; gills running down the stem point to a funnel.

The stem is 5-10 cm tall and 1-2.5 cm thick, firm and cylindrical, thickening toward the base when young. It's whitish to greyish, and pinkish-red spots often appear where it's damaged, a diagnostic feature. The surface is smooth with lengthwise fibres. There's no ring.

The stem is 3–8 cm tall and 0.8–1.5 cm thick, cylindrical, sometimes slightly wider at the base. It's white to pale yellowish brown, powdery at the top, finely fibrous lower down, and slowly browns when handled.

There is no ring, no veil remnants and no bag-like volva at the base. If you find such a sac, you're holding an amanita.

The flesh is firm and white and develops pinkish-red spots when cut or pressed, especially low in the stem, a characteristic reaction and an important diagnostic clue. The smell is distinctly soapy (laundry soap), and the taste is mealy or bitterish and unpleasant.

The flesh is white and firm, thick in the cap, and doesn't change colour noticeably when cut (some authors note a faint pink tint). The taste is acrid and burning, with bitterness.

Distinctly soapy, like laundry or toilet soap. It's a diagnostic feature, especially obvious when the mushroom is cut and in mature specimens.

The smell is strong and unpleasant: sharp like radish, with a sickly sweet note of honey and a mealy edge when cut. Young specimens smell less, mature ones can be smelt from a distance. A nauseating chemical smell, like cooked beetroot or coal gas, belongs more to its relatives, the chemical knight of birch woods and the gassy knight (Tricholoma inamoenum).