Pleurotus ostreatus, also known as the Oyster mushroom, is a medium to large fungus named for its shape rather than its taste. It grows almost all over the world and is fairly easily recognized by the way it grows on wood in shelf-like clusters and its whitish gills that run down a stubby, nearly-absent stem.

Cap convex with an incurved margin at first, expanding to a fan-shaped with a flat or shallowly depressed disc and inner limb. The cap colour is pale to dark brown, fading to buff, sometimes fading slowly and becoming two-toned. It may be somewhat greasy when young and fresh. The flesh is thick, white and unchanging when sliced. Gills running down the stem, crowded, whitish or with a grey tinge, becoming yellowish in age and sometimes developing brownish edges, and descend on the stalk if present. Stem off-centre with a lateral attachment to wood, whitish. It can sometimes be more or less central when growing on the tops of logs or branches. Spore print white to faintly yellowish, or pale lilac-grey.

Microscopic Features: The spores are subcylindrical to narrowly kidney-shaped, smooth, measuring 8-12.5 x 3-4.5µm.

Pleurotus ostreatus on the MushroomExpert.Com Web site.
Pleurotus ostreatus on the www.first-nature.com web site.