Cleistothecia and perithecia look identical to pycnidia of Deuteromycete fungi until the structure is crushed and viewed with a microscope to see the asci and ascospores. Examples of Ascomycetes include Botryoshaeria, Nectria, Sclerotinina, Didymella , and Guignardia . Deuteromycetes fungi consist of the largest group of plant pathogens. They are called imperfect fungi because their sexual stage is not known.
Some fungi produce their conidia on naked or open conidiophores.
Others produce their spores within fruiting body structures called acervuli or pycnidia. Pycnidia and perithecia of the Ascomycetes look identical on plant material, but spores are produced singularly within pycnidia. Spore characteristics vary greatly with this group. Examples of Deuteromycetes include Entomosporium, Cercospora, Phyllosticta, Botrytis, Colletotrichum , and Fusarium . In this booklet and fungal identification training, the majority of fungal references such as terms used for spores and fruiting structures are for Deuteromycete fungi.