Pileipellis

The pileipellis is the uppermost layer of hyphae in the pileus of a fungal fruit body.

A cutis is a type of pileipellis characterized by hyphae that are repent, that is, that run parallel to the pileus surface.

In a trichoderm, the outermost hyphae emerge roughly parallel, like hairs, perpendicular to the cap surface.

An epithelium is a pileipellis consisting of rounded cells in multiple layers, often connected in chains, and sometimes breaking off.

When viewed from above, a hymeniderm or "cellular cuticle" appears to be paved with roughly circular polygonal elements (similar to the fertile cells of the actual hymenium on the gills).

The cuticle of some mushrooms, such as Russula ochroleuca shown here, can be peeled from the cap, and may be useful as an identification feature.