This delightful fungi is extremely well known worldwide, often growing in beautiful bouquets, and can easily be 'hunted' at your local grocery store. The British have a penchant for nicknaming most any mushroom and they sometimes call it the "Shellfish of the Woods" but this pot hunter doesn't feel it tastes much like oysters or sea creatures at all. It does, however, go great in seafood dishes in a bit of cream sauce like Gloucester's Franklin Café's Cod with Oyster Mushrooms and Potatoes, a delicious dish. From early in the summer until deep into the winter you can find these growing out of fallen trees near waterways or often out of trees that have started to decline. They are saprobic decayers, not parasites, so all they are doing is helping decay the already increasing amount of dead tissue within the tree. With a few days of warmish weather in the winter, you can find these even in January. The plus side of late season hunting them is that they are completely bug free. In the summer you'd best cook them within hours lest the critters take over. If you find them in the wild, their flavor is double as good as the store-bought ones because they are growing out of natural substrate, often maples, beeches or hardwood trees.
Oysters grow in dense overlapping clusters, referred to as 'cespitose', and have fan-shaped caps loosely resembling oyster shells which vary in color from white or tan, to gray or brown. The darker their color the more you might wonder if you have a dangerous lookalike. Just be sure that they are growing directly out of wood, not the ground, and have a white to grayish-white spore color. You can easily determine spore color by setting a cap, gill-side down, on some dark paper overnight. Their gills always attach solidly to the stem and descend it a bit. This is known as having 'decurrent' gills, an important feature. Their stem is often completely absent or else off-center on the cap. The stems will not have a ring and neither the stem nor the cap will have scales or warts of any kind.
There are many similar mushrooms which are also edible, such as the Indian Oyster (Pleurotus pulmonarius), the Elm Oyster (Hypsizygus ulmarius) and many of the Oyster's close relatives which are cultivated and sold at stores that have even escaped into the wild such as the Blue, Pink and Golden Oyster. All are edible and fun to find. As always, before eating any wild mushroom, know the mushroom well and know their look-alikes. Happy hunting.
Gary Gilbert teaches mushrooms locally and through the Boston Mycological Club. He is also the originator of Mycocards.com, flashcards for learning mushrooms.