Fungi imperfecti

Fungi imperfecti are a group of fungi that scientists have found difficult to classify. They are also known by names like Deuteromycota, Deuteromycetes, or imperfect fungi. This group is unique because their sexual form of reproduction has never been observed. Most scientists group fungi based on their sexual structures or biological species concepts. Because these fungi only show asexual and vegetative phases, they do not fit into standard categories. This makes them a special subject of study in the field of mycology.

These fungi reproduce through a process called sporogenesis. In this process, the fungi produce spores asexually. This means they do not need a partner to create new life. Some fungi may be unable to reproduce sexually due to genetic mutations. Others might be sterile because of epigenetic changes. These changes can happen very quickly in a laboratory setting. In such environments, fungi may undergo 10 to 19 generations of only asexual reproduction. Some species even use a parasexual cycle. This allows them to mix genetic traits without undergoing actual sexual reproduction.

Historically, scientists used a complex dual system of nomenclature to name these organisms. This system was permitted by Article 59 of the International Code of Botanical Nomenclature. Under these rules, an asexual fungus was called a form taxon. For example, the common mold Aspergillus niger has no known sexual cycle. It was treated as a form taxon. However, if a sexual stage, called a teleomorph, was discovered, that name took priority. An example is Aspergillus nidulans, which is the anamorph of the sexual species Emericella nidulans. This dual system was abolished in a 2011 update to the Code.

Today, the classification of these fungi is changing through molecular systematics. This method uses comparative analyses of DNA sequences, such as rRNA or multigene phylogenies. Scientists use this data to build phylogenetic trees. These trees help researchers infer how asexual fungi relate to their sexual counterparts. This helps place them more accurately on the tree of life. However, this work is difficult. Researchers need large amounts of biological material, like spores or fresh specimens. These must come from pure, uncontaminated fungal cultures to be accurate.

There are approximately 25,000 species classified within the division Deuteromycota. Many of these are actually anamorphs of the Ascomycota or Basidiomycota groups. Scientists often use informal terms to describe them today. For instance, the term hyphomycetes is often used to refer to molds. The term coelomycetes refers to many plant pathogens that form discrete fruiting bodies. Some classifications, like those from Saccardo, group them by how they produce spores. They might lack fruiting bodies or produce spores in structures called acervuli or pycnidia.

Imperfect fungi play many important roles in human life and the environment. Some are used to create medicines, such as the antibiotic penicillin. Others are vital to the food industry. Species like Penicillium roqueforti and Penicillium camemberti give Roquefort and Camembert cheese their unique tastes. Some fungi are also used for industry, like Tolypocladium inflatum, which provides the immunosuppressant ciclosporin. However, some species can be harmful. The fungus Magnaporthe oryzae is a known pathogen that affects rice. Other species, like Lecanicillium, can produce conidia to control insect pests.

Modern science no longer formally accepts Fungi imperfecti as a single taxon. This is because the group does not follow the principle of monophyly. Monophyly means a group must include an ancestor and all its descendants. Since these fungi are grouped by what they lack, they do not meet this rule. Instead, they are being integrated into modern fungal classification through DNA research. This ongoing debate helps scientists better understand the complex relationships between all living fungi.