Russula xerampelina, also known as Crab Russula, is a medium to large agaric that has a hard-fleshed cap whose colour varies but is often dark red or purple. Mature mushrooms have a fishy odour. All parts slowly stain dingy yellow-brown when cut or bruised. The mushroom can be found in both deciduous and coniferous woodlands, often associating with trees such as oak, beech, pine, spruce, and fir. The species prefers well-drained soils and is often observed during the late summer and autumn months.

Cap convex, becoming later flat, with a broad, shallow depression. Surface sticky when moist, but soon dry; smooth - not streaked or warty. The Colour is most often dark red, but may be dark purple, pink, green or brown, often with traces of yellow. The flesh is white but discolouring slowly yellowish brown to brownish or brown when sliced. Gills broad, initially attached to the stem, but may separate as they mature. Close, crowded, or slightly spaced, changing from white/creamy to yellowish-orange as they age. Stem more or less equal, dry, fairly smooth and solid at first, later spongy. Surface white or flushed with pink. It has no ring. Spore print creamy, yellowish, or orangish yellow.

Microscopic Features: The spores are ellipsoidal, 8-11 x 6.5-8μm, with scattered isolated warts up to 0.8μm tall, not forming a closed network.

Russula xerampelina on the first-nature.com Web site.
Russula xerampelina on the MushroomExpert.Com Web site.