Sulphur knight or Prunes and custard

The cap is 3–8 cm across. Young caps are hemispherical or convex, then flatten out with a wavy margin, often keeping a low umbo in the centre, occasionally with a slight dip.

It is sulphur yellow, developing rusty-brown fibres in the centre with age, sometimes with an olive or reddish tinge. Some specimens have a purplish-brown cap: these were once described as a separate species, Tricholoma bufonium, but DNA work shows they are a form of the same species. The surface is dry, matt and slightly velvety, never slimy and without obvious scales.

The cap is 3-8 cm across, convex with an inrolled margin when young, becoming flat and spread out with a slightly sunken centre. The cap skin is dry and fibrous, golden yellow, densely covered in small grey-brown fibrous scales, especially in the centre. The base colour is golden yellow to yellow-orange.

The gills are sulphur yellow, broad, thick and widely spaced, notched where they meet the stem, with shorter gills in between and a slightly uneven edge. These distant, thick gills are what set it apart from the yellow knight, whose gills are crowded and thin.

The spore print is white. A purple-brown print, with gills that turn greenish and then dark, means you are looking at a sulphur tuft.

The gills are notched (emarginate) at the stem, crowded, fleshy and distinctly yellow. The spore print is white to cream.

The stem is 3–10 cm tall and 0.5–1.8 cm thick, cylindrical and firm. It is bright yellow at the top and sulphur yellow lower down, with reddish or brownish lengthwise fibres, and the base turns brownish in older specimens, sometimes with white down at the very bottom.

There is no ring, no veil remnants and no volva.

The stem is 3-7 cm tall and 0.5-1.2 cm thick, cylindrical, hollow in old mushrooms. It's yellowish to yellow-orange, with fine brownish-fibrous scales lower down, and the surface is dry and fibrous. There's no ring.

The flesh is sulphur yellow, sometimes greenish, all the way through the cap and stem, and doesn't change colour when broken. The taste is unpleasant, mealy and often bitter.

The flesh is yellowish, thin and cottony in the cap, rather tough in the stem, and doesn't noticeably change colour when cut. The smell is faintly mushroomy with a woody note, the taste mild with a sourish-bitter aftertaste.

The smell is very strong and unpleasant: coal tar, acetylene, old-fashioned coal gas, and to some people hydrogen sulphide. It comes from skatole, which in weaker doses can even seem floral, like jasmine or hyacinth. It is strongest on a freshly broken surface.

A paler form with only a faint smell does exist, so a mushroom that is yellow throughout with thick, widely spaced gills but little smell is still not necessarily a yellow knight. Always look at all the features together.

Faintly mushroomy with woody notes, not distinctive.