General Microbiology - Schlegel, H. 1987

Fungi
Fungi Imperfecti (Deuteromycetes)

This Class includes fungi in which the sexual (teleomorph) stage is absent or has not yet been discovered. The conidial stage in these fungi is very similar to that characteristic of well-studied ascomycetes. This suggests that imperfect fungi are nothing more than the conidial stage of ascomycetes whose ascus stage has either not yet been found or has been lost during the course of evolution.

However, one cannot speak of the complete absence of a Sexual process in imperfect fungi. Much like Basidiomycetes and other ascomycetes, they have been proven to exhibit a parasexual process. Plasmogamy, karyogamy, and Meiosis do occur in them, but not in specific Regions of the vegetative body nor at predetermined Selection/3.html">Stages of development. Normally, the primary mycelium of imperfect fungi is homokaryotic, meaning it contains nuclei of only a single type. Heterokaryons arise As a result of the fusion of protoplasts containing Different types of nuclei. A foreign Nucleus introduced into the mycelium multiplies, and the resulting daughter nuclei spread throughout the mycelium. Periodically, karyogamy and meiosis take place. Thus, the parasexual cycle provides a recombination of nuclear material nearly as efficient as a true sexual process.

The Classification of imperfect fungi is based on spore-bearing structures and other external features, serving purely practical purposes for nomenclature and identification.