How to tell Birch knight from Brown rollrim

The cap is 4–12 cm across, occasionally up to 15 cm. Young caps are convex, then flatten, often with a low umbo, and can be slightly sunken in the centre.

The colour is reddish brown to yellowish brown: darker in the centre, paler and yellowish at the margin. Fine brown fibres radiate from the centre. The skin is sticky, slimy and shiny in wet weather and matt when dry. The margin is often grooved, and old caps may crack into small scales.

Cap 5–15 cm across, convex in young mushrooms, then depressed or funnel-shaped. Surface smooth, hairy-felty in young ones, almost bare in mature ones, olive brown or yellowish brown, sticky in wet weather. The margin stays rolled under for a long time — a characteristic feature.

The gills are crowded, fairly broad and notched where they meet the stem. Young gills are pale yellow or yellowish white, and with age they develop rusty brown spots, with brownish edges.

Yellowish gills are unusual in the genus: most knights, including the poisonous brown ones, have white or cream gills. The spore print is white.

Gills crowded, thin, ochre-yellow or olive, easily separating from the flesh when pressed, browning when damaged. They run down the stem. This tendency to brown when pressed is a useful identification feature.

The stem is 4–13 cm tall and 0.7–2 cm thick, cylindrical, sometimes thickening towards the base. It's coloured like the cap but paler, yellowish brown, lighter at the top, and streaked with darker brown lengthways fibres.

Young stems are solid and slightly sticky; old ones become hollow. There is no ring and no volva.

Stem 3–8 cm tall, 1–2 cm thick, firm, solid, cylindrical or tapering downward, the same colour as the cap or slightly paler. No ring and no volva.

The flesh is firm. It's whitish to pale yellow in the cap and distinctly yellow in the stem, and that's the easiest way to tell the birch knight from other brown knights, whose flesh is white. It doesn't change colour when cut. The taste is mealy, sometimes slightly bitter.

Flesh yellowish cream or brownish, firm in young ones, looser in mature ones. Browns when damaged. Has a slightly acrid or sourish taste. Does not exude milk.

The smell is mealy, like raw dough, sometimes with a hint of cucumber. It's not much help for identification: some poisonous brown knights smell of flour too.

Smell sourish and pleasant, like fruit or vinegar, especially in mature mushrooms. This neutral, even pleasant smell is exactly what helped the mushroom pass as edible for so long.