Classification of Fungi by Alexopoulos and Mims: A Review and Update

Classification Of Fungi Alexopoulos And Mims 1979 Pdf 27

Fungi are one of the most diverse and fascinating groups of living organisms. They play vital roles in many ecosystems, such as decomposing organic matter, forming symbioses with plants and animals, producing useful substances, and causing diseases. However, fungi are also very challenging to classify because they have complex and varied evolutionary histories and show many variations in their morphology and physiology.

Classification Of Fungi Alexopoulos And Mims 1979 Pdf 27

Many attempts have been made by mycologists to develop a natural and comprehensive classification system for fungi based on their vegetative and reproductive characteristics. One of the most influential and widely used systems was proposed by Constantine J. Alexopoulos and Charles W. Mims in 1979. In this article, we will explore the main features and principles of this system and its advantages and limitations.

The Classification System by Alexopoulos and Mims

Alexopoulos and Mims (1979) classified fungi and slime molds as belonging to the superkingdom Eukaryonta's Myceteae. They divided the kingdom into three divisions: Gymnomycota, Mastigomycota, and Amastigomycota. Each division was further subdivided into subclasses, classes, form-classes, orders, families, genera, and species.

The main criteria used by Alexopoulos and Mims to classify fungi were the presence or absence of flagella, the type of spores produced, the mode of sexual reproduction, and the structure of the thallus (the vegetative body of fungi). They also considered other features such as pigmentation, septation, hyphal branching, cell wall composition, and biochemical properties.

The following is a brief summary of the three divisions and their main characteristics:

Gymnomycota

This division includes fungi and slime molds that lack a cell wall or have a very thin one. They have a naked protoplasmic mass called plasmodium that can move by amoeboid or streaming movements. They produce spores by simple cleavage or budding. They do not have a sexual cycle or produce gametes.

The Gymnomycota are divided into two subdivisions: Acrasiogymnomycotina and Plasmodiogymnomycotina. The former includes cellular slime molds that form aggregations of individual cells that act as pseudoplasmodia. The latter includes true slime molds that form multinucleate plasmodia that can differentiate into fruiting bodies.

Mastigomycota

This division includes fungi that have flagellated cells or spores at some stage of their life cycle. They have a cell wall composed of cellulose or chitin. They produce spores by mitosis or meiosis. They have a sexual cycle that involves gametes or gametangia (specialized hyphal branches).

The Mastigomycota are divided into two subdivisions: Haplomastigomycotina and Diplomastigomycotina. The former includes chytrids, hyphochytrids, and plasmodiophorids that have unicellular or coenocytic thalli and produce zoospores (motile spores) with a single posterior flagellum. The latter includes oomycetes that have filamentous thalli with cross walls (septa) and produce zoospores with two anterior flagella.

Amastigomycota

This division includes fungi that lack flagellated cells or spores in their life cycle. They have a cell wall composed of chitin or chitosan. They produce spores by mitosis or meiosis. They have a sexual cycle that involves plasmogamy (fusion of cytoplasm), karyogamy (fusion of nuclei), and meiosis.

The Amastigomycota are divided into three subdivisions: Zygomycotina, Ascomycotina, and Basidiomycotina. The former includes zygomycetes and trichomycetes that have coenocytic thalli and produce zygospores (thick-walled resting spores) as a result of sexual reproduction. The latter two include ascomycetes and basidiomycetes that have septate thalli and produce ascospores (spores inside sac-like structures called asci) or basidiospores (spores on club-shaped structures called basidia) as a result of sexual reproduction.

Advantages and Limitations of the Classification System by Alexopoulos and Mims

The classification system by Alexopoulos and Mims was based on extensive morphological, physiological, biochemical, and cytological studies of fungi. It was widely accepted by mycologists because it provided a clear and logical framework for identifying and grouping fungi according to their natural affinities. It also reflected some aspects of their evolutionary relationships.

However, the classification system by Alexopoulos and Mims also had some limitations and drawbacks. It was not completely natural or phylogenetic because it did not take into account molecular data such as DNA sequences or protein structures that could reveal more accurate evolutionary histories of fungi. It also did not account for some anomalies or exceptions among fungi that did not fit well into the proposed categories. For example, some fungi had flagella in their ancestors but lost them later; some fungi had both zoospores and ascospores; some fungi had intermediate forms between asci and basidia; some fungi had multiple sexual cycles; etc.

Therefore, the classification system by Alexopoulos and Mims was not final or definitive but rather provisional and tentative. It was subject to revision and modification as new information became available from molecular biology, genetics, ecology, biogeography, paleontology, etc. Many mycologists have proposed alternative or complementary systems that incorporate molecular data or other criteria to classify fungi more naturally and phylogenetically.

Conclusion

Classification Of Fungi Alexopoulos And Mims 1979 Pdf 27 is a keyword that refers to a classification system for fungi proposed by Constantine J. Alexopoulos and Charles W. Mims in 1979. This system divided fungi into three divisions based on their flagellation, spore production, sexual reproduction, and thallus structure. It was widely used by mycologists because it provided a clear and logical framework for identifying and grouping fungi according to their natural affinities. However, it also had some limitations and drawbacks because it did not take into account molecular data or other criteria that could reveal more accurate evolutionary histories of fungi. Therefore, it was subject to revision and modification as new information became available from various sources. ca3e7ad8fd