peridium

Peridium is the outer wall or covering of the fruiting body in certain fungi, especially the gasteroid forms such as puffballs and earthstars. It encloses the spore-bearing tissue, the gleba, and may consist of one or more layers. In many puffballs the outer layer is called the exoperidium, with an inner layer—the endoperidium—that surrounds the gleba. As the fruiting body matures, the endoperidium may rupture, or the peridium may be shed, to enable spore release through pores or openings.

The peridium can be persistent or fragile, and its surface may be smooth, rugose, pigment-rich, or sculptured. In earthstars, the peridium splits into rays that peel back to expose the central spore sac. Peridiac morphology, including the number of layers and how the wall breaks, is an important taxonomic character and often correlates with ecological strategies, such as spore dispersal mechanisms.

In contrast to botanical terminology, the peridium is a fungal term and should not be confused with the plant pericarp, the fruit wall surrounding a seed-containing structure. Notable examples of fungi with a well-defined peridium include Calvatia gigantea (giant puffball) and Lycoperdon species (puffballs). The study of peridia aids in identification and understanding of the developmental biology of these fungi.