Pleurocystidia

Pleurocystidia are specialized sterile cells found on the hymenium, the spore-bearing surface, of some fungi, particularly in the order Agaricales. These structures are typically found interspersed among the basidia, which are the cells that produce spores. Pleurocystidia are generally larger and more distinctly shaped than the basidia and can vary significantly in morphology depending on the fungal species. Their function is not fully understood, but proposed roles include protection of the basidia and developing spores, dispersal of spores, or even acting as a chemical deterrent against fungivores.

The presence, absence, and morphology of pleurocystidia are important diagnostic features used in fungal taxonomy and identification. Microscopists examine these cells to distinguish between closely related species or genera. Characteristics such as their shape (e.g., fusiform, clavate, lageniform), wall thickness, presence or absence of encrustations or internal contents, and refractive properties under microscopy are all key identifying traits. Their distribution on the hymenium, whether scattered or abundant, also contributes to their taxonomic value. Some fungi possess cystidia on the cap margin (cheilocystidia) or stipe surface (caulocystidia) in addition to pleurocystidia.