hymenium

Hymenium is the spore-bearing tissue layer of a fungal fruiting body. It is the part of the fungus where reproductive cells are produced and released as spores. The hymenium is typically comprised of specialized hyphae: basidia or asci, depending on the fungal lineage, and may include sterile supporting cells such as paraphyses.

In Basidiomycota, the hymenium contains basidia, each producing four basidiospores after meiosis. In Ascomycota, the hymenium contains asci, each typically containing eight ascospores formed by meiosis. The exact arrangement and density of hymenial elements vary with species and fruiting-body form.

The hymenium is usually located on surfaces that become exposed as the fruiting body matures, such as the gills of mushrooms, the pores of polypores, or the inner surface of cups and bowls. It is bordered by sterile tissue above and below in many forms and is protected by the outer skin or cap when present.

In lichenized fungi the term also describes the spore-bearing layer of the apothecium. Microscopically, the hymenium is examined to identify the presence of basidia, asci, spores, and paraphyses, which are important for taxonomy.