Tricholoma fulvum, also known as the Birch Knight, is a large fleshy agaric commonly found in association with birch trees, from which it gets its common name. This species is recognized by its brownish cap and yellowish gills, which take on a yellowish hue as it matures. The mushroom grows scattered or in small trooping groups on soil in broad-leaf and mixed woods, favouring birch and spruce.

Cap reddish-brown with fine, radiating fibrils. Initially convex, it becomes flattened with age, sometimes developing a slight umbo. The surface is smooth and slightly sticky. The flesh is white and thick. Gills bright yellow, eventually developing brown spots, and are adnexed or emarginate. Stem more or less equal, either smooth or finely silky, often with a white zone at the extreme apex, but brownish elsewhere. The stem has no ring. Spore print white.

Microscopic Features: The spores are subglobose to oblong, smooth, and measure 5-7 x 4-5 μm.

Tricholoma fulvum on the first-nature.com Web site.