The hymenium is the layer of tissue on the hymenophore of the part of a fungus that fruits. It is where cells grow into basidium or asci, which make spores.

Where the hymenium is found is traditionally the first thing used to identify mushrooms or to group mushrooms into families. Below are some examples of where to find the hymenium in different types of Basidiomycota and Ascomycota.

• In agarics, the hymenium is on the flat sides of the gills.
• In boletes, it is in a spongy mass of tubes that point down.
• In puffballs, it is on the inside.
• In stinkhorns, it grows on the inside and then comes out as a bad-smelling gel.
• In cup fungi, it is on the inner surface of the cup.
• In teeth fungi, it grows on the outside of tooth-like spines.