Acervuli

Acervuli are a type of fungal asexual fruiting body, or conidiomata, found on the surfaces of plant tissues. The singular form is acervulus and the plural is acervuli. They represent cushion-like or pancake-shaped masses of hyphae and conidiophores that develop directly on or just beneath the epidermis of host tissue, often within the decaying or aged tissue.

Morphologically, acervuli produce conidia (asexual spores) in a loose, conidiogenous mass exposed on the surface. They are typically open to the exterior, not enclosed by a defined wall or ostiole, and can be accompanied by a gelatinous matrix or exudate that helps in spore dispersal. Conidia produced in acervuli are usually dispersed by wind, rain splash, or physical contact, contributing to the spread of the fungus and often to disease symptoms on the host.

Acervuli are characteristic of many plant-pathogenic ascomycetes and related fungi, including genera such as Colletotrichum and Alternaria. They are an important diagnostic feature in plant pathology, helping to distinguish the asexual reproductive strategy from other structures such as pycnidia or stromatic fruiting bodies. The formation of acervuli typically correlates with active infection and disease progression, making humidity and leaf wetness key factors in the epidemiology of affected crops.

In summary, acervuli are open, surface-associated conidiomata that produce conidia for rapid dissemination, playing a central role in the asexual phase and spread of several plant-pathogenic fungi. See also pycnidia and other conidiomata for related reproductive structures.