Hypsizygus ulmarius 

Hypsizygus ulmarius (Bull.) Redhead 1984

This is in the Lyophyllaceae family in the Agaricales order of the Basidiomycota.

Unlike Pleurotus dryinus (in the Pleurotaceae family) and Lentinus levis (in the Polyporaceae family), the cap of the ‘Elm Oyster’ is creamy white, smooth rather than fuzzy, and the gills are not decurrent. Also, the margins of the ’Elm Oyster’ have a tendency to crack as they expand, unlike the others. Finally, there is no evidence of a ring on the stem. Edible.