A primitive plant that obtains its nourishment either saprophytically, by secreting enzymes to dissolve insoluble organic food externally before absorption, or parasitically, by absorbing food from a host. The body form may be single-celled, but usually consists of a network (mycelium) of thread-like strands (hyphae) which may produce a compact, fruiting body bearing the reproductive tissues. Cell walls are usually made of chitin, occasionally of cellulose. The true fungi belong to the division Eumycota of the kingdom Plantae, containing all fungi except the slime moulds and their allies. Fungi are sometimes classified as a separate kingdom characterized by their lack of flagella at all stages of the life-cycle; those with flagella are transferred to the kingdom Protoctista. Fungi fulfil a vital ecological role in recycling nutrients. Many are pests of crops or are human pathogens; some are edible or produce useful by-products.
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iFungi Fossil range: Early Silurian - Recent |
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Amanita muscaria, a basidiomycete |
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Chytridiomycota |
The fungi (singular fungus) are a kingdom of eukaryotic organisms. Yeasts, molds, and mushrooms are examples of fungi. The branch of biology involving the study of fungi is known as mycology.
Fungi often have important symbiotic relationships with other organisms. Mycorrhizal symbiosis between plants and fungi is particularly important; over 90% of all plant species engage in some kind of mycorrhizal relationship with fungi and are dependent upon this relationship for survival. Fungi are also used extensively by humans: yeasts are responsible for fermentation of beer and bread, and mushroom farming and gathering is a large industry in many countries.
Fungi and bacteria are the primary decomposers of organic matter in most terrestrial ecosystems.
Phylogeny and classification of fungi
Fungi were originally classified as plants, however they have since been separated as they are heterotrophs. Fungi are now thought to be more closely related to animals than to plants, and are placed with animals in the monophyletic group of opisthokonts. For much of the Paleozoic Era, the fungi appear to be aquatic. The first land fungi probably appeared in the Silurian, right after the first land plants appeared, even though their fossils are fragmentary. Fungi absorb their food while animals ingest it; also unlike animals, the cells of fungi have cell walls.
The Fungi are a monophyletic group, meaning all varieties of fungi come from a common ancestor. The monophyly of the fungi has been confirmed through repeated tests of molecular phylogenetics;
The taxonomy of the Fungi is in a state of rapid flux at present, especially due to recent papers based on DNA comparisons, which often overturn the assumptions of the older systems of classification.
Types of fungi
The major divisions (phyla) of fungi are mainly classified based on their sexual reproductive structures. These fungi produce zoospores that are capable of moving on their own through liquid menstrua by simple flagella. Members of the Glomeromycota are also known as the arbuscular mycorrhizal fungi. The Ascomycota, commonly known as sac fungi or ascomycetes, form meiotic spores called ascospores, which are enclosed in a special sac-like structure called an ascus. Members of the Basidiomycota, commonly known as the club fungi or basidiomycetes, produce meiospores called basidiospores on club-like stalks called basidia. Most common mushrooms belong to this group, as well as rust (fungus) and smut fungi, which are major pathogens of grains.
Although the water moulds and slime moulds have traditionally been placed in kingdom Fungi and are still studied by mycologists, they are not true fungi. Unlike true fungi, the water moulds and slime moulds do not have cell walls made of chitin.
Structure
Fungi may be single-celled or multicellular. Multicellular fungi are composed of networks of long hollow tubes called hyphae. Because fungi are embedded in the medium in which they grow, they are often not visible to the naked eye.
Although fungi lack true organs, the mycelia of ascomycetes and basidiomycetes may become organized into more complex reproductive structures called fruiting bodies, or sporocarps, when conditions are right. Some fungi form rhizoids, which are underground root-like structures that provide support and transport nutrients from the soil to the rest of the mycelium.
A fungus of the species Armillaria ostoyae may be the largest organism on the planet.
Reproduction
Fungi may reproduce sexually or asexually. Sexual reproduction has not been observed in some fungi of the Glomeromycota and Ascomycota. These are commonly referred to as Fungi imperfecti or Deuteromycota.
Yeasts and other unicellular fungi can reproduce simply by budding, or “pinching off” a new cell.
Sexual reproduction in fungi is somewhat different from that of animals or plants, and each fungal division reproduces using different strategies. Fungi that are known to reproduce sexually all have a haploid stage and a diploid stage in their life cycles.
In zygomycetes, the haploid hyphae of two compatible individuals fuse, forming a zygote, which becomes a resistant zygospore.
In ascomycetes, when compatible haploid hyphae fuse with one another, their nuclei do not immediately fuse.
Sexual reproduction in basidiomycetes is similar to that of ascomycetes.
Ecological role
Although often inconspicuous, fungi occur in every environment on Earth and play very important roles in most ecosystems. Along with bacteria, fungi are the major decomposers in most terrestrial (and some aquatic) ecosystems, and therefore play a critical role in biogeochemical cycles and in many food webs.
Many fungi are important as partners in symbiotic relationships with other organisms, as mutualists, parasites, or commensalists, as well as in symbiotic relationships that do not fall neatly into any of these categories. One of the most critically important of these relationships are various types of mycorrhiza, which is a kind of mutualistic relationship between fungi and plants, in which the plant's roots are closely associated with fungal hyphae and other structures. The fungi also protect against diseases and pathogens and provide other benefits to the plant. Over 90% of the plant species on Earth are dependent on mycorrhizae of one type or another in order to survive, and it is hypothesized that the presence of terrestrial fungi may have been necessary in order for the first plants to colonize land.
Lichens are formed by a symbiotic relationship between algae or cyanobacteria (referred to in lichens as "photobionts") and fungi (mostly ascomycetes of various kinds and a few basidiomycetes), in which individual photobiont cells are embedded in a complex of fungal tissue.
Certain insects also engage in mutualistic relationships with various types of fungi. Several groups of ants cultivate various fungi in the Agaricales as their primary food source, while ambrosia beetles cultivate various kinds of fungi in the bark of trees that they infest.
Some fungi are parasites on plants, animals (including humans), and even other fungi. Pathogenic fungi are responsible for numerous diseases, such as athlete’s foot and ringworm in humans and Dutch elm disease in plants. Some fungi are predators of nematodes, which they capture using an array of devices such as constricting rings or adhesive nets .
Human uses of fungi
Fungi have a long history of use by humans. Many types of mushrooms and other fungi are eaten, including button mushrooms, shiitake mushrooms, and oyster mushrooms. Fungi are also used to produce industrial chemicals like lactic acid, antibiotics and even to make stonewashed jeans. Some types of fungi are ingested for their psychedelic properties, both recreationally and religiously (see main article, Psychedelic mushroom).
Edible and poisonous fungi
Some of the most well-known types of fungi are the edible and poisonous mushrooms. Other commercially-grown mushrooms that have gained in popularity in the West and are often available fresh in grocery stores include straw mushrooms (Volvariella volvacea), oyster mushrooms (Pleurotus ostreatus), shiitakes (Lentinula edodes), and enokitake (Flammulina spp.).
There are many more mushroom species that are harvested from the wild for personal consumption or commercial sale.
It is also a common practice to permit the growth of specific species of mold in certain types of cheeses that give them their unique flavor.
Hundreds of mushroom species are toxic to humans, causing anything from upset stomachs to hallucinations to death.
Fly agaric mushrooms (A.
Fungi in the biological control of pests
Many fungi compete with other organisms, or directly infect them. Some of these fungi are considered beneficial because they can restrict, and sometimes eliminate, the populations of noxious organisms like pest insects, mites, weeds, nematodes and other fungi, such as those that kill plants. There is much interest on the manipulation of these beneficial fungi for the biological control of pests. Some of these fungi can be used as biopesticides, like the ones that kill insects (entomopathogenic fungi). Specific examples of fungi that have been developed as bioinsecticides are Beauveria bassiana, Metarhizium anisopliae, Hirsutella, Paecilomyces fumosoroseus, and Verticillium lecanii (=Lecanicillium lecanii ).
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