Cleistothecia

Cleistothecia are a type of sexual fruiting body (an ascocarp) found in some ascomycetous fungi. They are completely enclosed by a tough wall and lack an opening to the outside, such as an ostiole, making them closed structures. Inside, asci develop and produce ascospores, typically eight per ascus, which are released only when the structure is disrupted or degraded.

Morphology and development vary, but cleistothecia are generally spherical to ovoid and range from a few hundred micrometers to about a millimeter in diameter. The outer wall, called the peridium, is formed from aggregated hyphal tissue and may be embedded in plant tissue, soil, or litter. The inner region contains numerous asci with ascospores arranged within a compact matrix. Cleistothecia arise during sexual reproduction and represent a means of survival and genetic recombination for the fungus.

Ecology and significance vary by group. Cleistothecia function as overwintering or long-term survival structures in several plant-associated fungi, including powdery mildews (order Erysiphales) and some species of Aspergillus and Penicillium. In many plant pathogens, cleistothecia provide a source of primary inoculum for new infections in favorable conditions after periods of dormancy. Spores are typically released when the outer wall breaks down or the structure decays, at which point they can disperse by wind or other vectors.

Taxonomically, cleistothecia are one of the major types of ascomata, distinguished from open fruiting bodies like apothecia and from flask-shaped perithecia by their completely closed structure. They are most notable for their role in the life cycles of several economically important fungi.