Tricholoma sulphureum, also known as the Sulphur Knight, is a medium-sized agaric distinguished by its bright sulphur-yellow colour and exceptionally strong, unpleasant odour, often compared to coal gas. The cap, gills and stem are all predominantly yellow, making this species quite distinctive. It grows in deciduous and mixed woodland, forming mycorrhizal associations mainly with beech and oak, although it may occasionally occur with conifers. It typically fruits from late summer to autumn, but can sometimes appear as early as late spring.

Cap convex when young, later flattening or becoming slightly depressed while usually retaining a broad central umbo. The surface is dry and matt, sulphur yellow in colour, often with reddish-brown, olive or occasionally purplish tinges, particularly towards the centre. The margin may become irregular or wavy with age. Gills bright sulphur yellow, broad, relatively thick and widely spaced. They are sinuate or notched where they approach the stem. Stem yellow, cylindrical and dry, sometimes marked with sparse reddish or brownish longitudinal fibres. The stem has no ring. Spore print white.

Microscopic Features: The spores are ellipsoidal and smooth, measuring 9-12 x 5-6.5 µm. They have a pronounced hilar appendage and are inamyloid, meaning they do not stain with iodine-based reagents.

Tricholoma sulphureum on the www.first-nature.com Web site.
Tricholoma sulphureum on Wikipedia.