As always with one fungus it is an assumption! "Pleurotus pulmonarius, commonly known as the Indian Oyster, Italian Oyster, Phoenix Mushroom, or the Lung Oyster, is a mushroom very similar to Pleurotus ostreatus, the pearl oyster, but with a few noticeable differences. The caps of pulmonarius are much paler and smaller than ostreatus and develops more of a stem. P. pulmonarius also prefers warmer weather than ostreatus and will appear later in the summer. Otherwise, the taste and cultivation of the two species is generally described as largely the same. In North America, P. pulmonarius also closely resembles Pleurotus populinus, which is restricted to growing on aspen and cottonwood." --https://fungusid.com