This page will cover some of the basics for Pleurotus - the Oyster mushrooms. As with all of these pages, they are NOT intended to be used as a key or diagnostic tool, but a guide of basic identifying characteristics so that you can make informed decisions and easy-access to other, more detailed resources.
What They Have In Common
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/levis, 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
This is one of the most convincing look-a-likes, sometimes even called the "mock-oyster". Phyllotopsis nidulans has a densely hairy texture to the cap and is usually some orange color and the fruitbody often smells foul.
Photo by Richard Davis
Please remember to seek other sources for confirmation before consuming any wild mushroom