Pileus (mycology)

In mycology (the branch of biology that includes the study of mushrooms and other fungi), the pileus is the technical name for the cap, or cap-like part, of a basidiocarp or ascocarp (fungal fruiting body) that supports a spore-bearing surface, the hymenium.

[1] The hymenium (hymenophore) may consist of lamellae, tubes, or teeth, on the underside of the pileus.

A pileus is characteristic of agarics, boletes, some polypores, tooth fungi, and some ascomycetes.

Convex pilei often continue to expand as they mature until they become flat.

Some, such as the parasol mushroom, have distinct bosses or umbos and are described as umbonate.