A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which are separate from plants, animals, and bacteria. This fungal group is distinct from the structurally similar slime molds and water molds. The discipline of biology devoted to the study of fungi is known as “mycology”, which is often regarded as a branch of botany, even though genetic studies have shown that fungi are more closely related to animals than to plants. Abundant worldwide, most fungi are subtle because of the small size of their structures, and their cryptic lifestyles, the ability of an organism to avoid observation by other organisms in soil, on dead matter, and as symbionts of plants, animals, or other fungi. Symbiosis is close and often long-term interactions between different biological species. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi are used industrially and in detergents. Fungi are also used as biological pesticides to control weeds, plant diseases and insect pests.
How many species of fungi have been identified so far?
There are about 75,000 scientifically identified species of fungi, with scientists believing that there may be as many as a million fungal species yet to be identified. As differing species of fungi may look the same apparently, classifying them accurately is difficult, and usually requires the application of molecular tools such as DNA sequencing. Since, DNA sequencing is still expensive, even for fungi with genomes far shorter than mammals, it will likely be many decades before the majority of fungi are classified with certainty.
What is the History of classification of fungi?
Ever since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus, a Swedish botanist, Christian Hendrik Persoon, a mycologist and Elias Magnus Fries, a botanist, fungi have been classified according to their morphology (e.g., characteristics such as spore color or microscopic features) or physiology. Fungal classification at the phyla level is complicated, and is constantly being reshuffled. Fungi were first misclassified as plants, but subsequent investigations found they actually have more in common with animals. Like plants and animals, fungi are eukaryotes. General fungi include molds — which grow in strands called hyphae, mushrooms — fruiting bodies of fungal colonies, and yeasts — the name for any single-celled fungi. But, these are broad terms, and molds, yeasts, and mushrooms can be found across several taxonomic categories of fungi.
How are fungi classified?
The 75,000 identified species of organisms commonly classified together as fungi are customarily divided into eight phyla, or divisions:
Chytridiomycota, or chytrids: This is the most ancient form of fungi, with about 1,000 identified species. These produce spores with flagella (zoospores), and go after amphibians, maize, alfalfa (Alfalfa is a plant used widely as animal feed), potatoes, and other vulnerable organisms. These are most representative of fungi that lived throughout the Paleozoic era, being mainly aquatic. A spore is a unit of asexual reproduction adapted to spending a long period of time in unfavorable conditions before developing into an offspring.
Blastocladiomycota: It is the second phlya of fungi, only created as a distinct category in 2007. Like the chytrids, they use zoospores to reproduce, and parasitic of all major eukaryotic groups.
Neocallimastigomycota: This is third phyla,and are anaerobic fungi that mainly dwell in the stomachs of ruminants. Their name contains the Greek suffix referring to whips, “mastix”, for their numerous flagella. The second and third phyla were both initially misclassified as chytrids.
Zygomycota: The fourth phyla of fungi are the more familiar Zygomycota, named for the hardy spherical spores they produce. Zygomycota includes black bread mold and molds, one of the most often viewed fungi by humans. Most are soil-living saprobes that feed on dead animal or plant remains. Some are parasitic of plants or insects. They reproduce sexually and form tough zygospores. There is no distinguishable male or female. There are over 600 species of this genus. The other one is Pilobolus, a fungus capable of ejecting spores several meters through the air.
Glomeromycota: This is the fifth phyla of fungi and is the known as “Arbuscular mycorrhizae (AM) fungi”.Typically, that term means “tree fungi.” Tree fungi can be found in large numbers in the roots of more than 80% of families of vascular plants. This relationship is symbiotic and ancient, extending back at least 460 million years, to the beginning of plant life on land.
Ascomycota: This is the sixth phyla of fungi and is known as “sac fungi”. This makes different spherical sacs to hold their spores, and has the most species out of all the fungi. Examples include Penicillium, edible types of morels, truffles, Baker’s yeast, lichens, powdery mildews, the black and blue-green molds and many others. Most of these phyla are plant-pathogenic. There are over 50,000 species, about 25,000. Their life cycle is a complex combination of sexual and asexual reproduction.
Basidiomycota or the club fungi: This is the seventh phyla of fungi. This group contains most common mushrooms. It is eminent by the presence of a spore-producing structure called the ‘basidium’, usually known as a ‘cap’. Along with Ascomycota, the club fungi are known as ‘Higher Fungi’. This includes the gill fungi (most mushrooms), the pore fungi (e.g., the bracket fungi, which grow shelf like on trees, and an edible type called tuck-a-hoe). It also includes the fungi that cause smut and rust in plants.
Deuteromycota: This phyla encompasses a copious assortment of fungi that do not fit tidily in other divisions; they have in common an apparent lack of sexual reproductive features. Also called “Fungi Imperfecti”, these cause diseases of plants and of animals (e.g., athlete's foot and ringworm), and that produce penicillin. A number of the fungi classified as deuteromycetes have been found to be asexual stages of species in other groups, and some classification schemes consider the deuteromycetes a class under Ascomycota.