Oysterlings are small whitish or brownish fungi found on twigs and branches, often darkening with age.  They are stemless or with rudimentary stipes and are attached to the substrate laterally (via one side of the cap, forming brackets) or centrally (via the cap, forming circular, shell-shaped or kidney shaped fans).  The gills fan out from the point of attachment.  Spores are brownish, ochre or buff.   There are several species that are difficult to identify. 

Oyster fungi (Pleurotus) are usually larger. 

Photograph upper and underside, and in situ on the substrate.

dead wood, including twigs

common