We have four primary species of Pleurotus in Alabama: P. ostreatus , P. pulmonaris, P. dryinus, and P. laevis. All four are edible and share the following characteristics: decurrent gills, growing on wood (maybe buried), convex or slightly depressed cap with an in-rolled margin when young, and dense, easily obtained white spore-prints. Oysters are a favorite for low-maintenance mushroom growing at home that is sometimes as easy as bringing home an infected log/branch and keeping it moist.
Pleurotus sp have a slightly hidden feature that helps distinguish them from some look-a-likes, they have a diaphanous margin (light is able to pass through). While several mushrooms have a diaphanous margin, Pleurotus are one of the few wood-growing mushrooms to display this so well. Don't depend on this feature, but it's something to keep in mind.
Pleurotus ostreatus are considered the "true oyster" and are stimulated to fruit by drops in the temperature, so expect to see these in fall-winter. P. ostreatus tend to fruit in clusters, almost shelves as seen in the image above. Caps are often buff/tan and usually covered in the white spores of those fruitbodies directly above them.
Pleurotus have several possible cap shapes that are heavily influenced by the environment but typically like to grow as above, with an off-center stipe and cap protruding away from the substrate. The off-center cap is slightly more typical of P. ostreatus than P. dryinus/l(a)evis, which can have more central stipes.
Frankly, these two species are difficult to separate both morphologically and microscopically, so we won't bother. Both may have a finely hairy-to-velvety cap surface and a stipe ornamented with fuzz. They are less likely to grow in shelves and fruit when warm-to-cool temperatures following good precipitation. Gills may be more distant than P. ostreatus, but are still close. I find that these species have a more defined boundary between their gills and the stipe, likely due to the ornamentation.
Photo by Cyndee Helms
The "summer oyster" is a rather delicate species and prefers the warmer months to fruit.
These "Pleurotoid" mushrooms drop a brown spore-print and lack of stem. They can come in a variety of white-to-brown colors and are often delicate.
This genus grows on wood and will have a central stipe without decurrent gills. The gills will start white and turn a salmon color as the pink spores drop