Fungi definition of Fungi in the Free Online Encyclopedia.

Fungi (fŭn`jī), kingdom of heterotrophic single-celled, multinucleated, or multicellular organisms, including yeasts, molds, and mushrooms. The organisms live as parasites parasite, plant or animal that at some stage of its existence obtains its nourishment from another living organism called the host. Parasites may or may not harm the host, but they never benefit it.
..... Click the link for more information. , symbionts, or saprobes (see saprophyte saprophyte (săp`rəfīt')
..... Click the link for more information. ). Previously classified in the plant kingdom, fungi are nonmotile, like plants, but lack the vascular tissues (phloem and xylem) that form the true roots, stems, and leaves of plants. Most coenocytic (multinucleated) or multicelluar fungi are composed of multiple filaments, called hyphae, grouped together into a discrete organism called a mycelium. The cell walls of fungi are of chitin or other noncellulose compounds. In many ways fungi are more closely related to animals than to plants, and they have been thought to share a common protist ancestor with animals. A recent classification system suggested by nucleic acid (genetic material) comparisons places the fungi with the animals and the plants in an overarching taxonomic group called the eukarya.

Most fungi are capable of asexual and sexual reproduction reproduction, capacity of all living systems to give rise to new systems similar to themselves. The term reproduction may refer to this power of self-duplication of a single cell or a multicellular animal or plant organism.
..... Click the link for more information. . Asexual reproduction is by fragmentation or spore spore, term applied both to a resistant or resting stage occurring among various unicellular organisms (especially bacteria) and to an asexual reproductive cell produced by many unicellular plants and animals and by all plants that undergo an alternation of
..... Click the link for more information. formation. Those that reproduce sexually produce gametes in specialized areas of the hyphae called gametangia. The gametes may be released to fuse into spores elsewhere, or the gametangia themselves may fuse. In some cases dikaryons [di = two, karyo = nucleus], which are found only among fungi, result when unspecialized hyphae fuse but their nuclei remain distinct for part of the life cycle.

Unlike algae or plants, fungi lack the chlorophyll necessary for photosynthesis and must therefore live as parasites or saprobes (see parasite). Typically they release digestive enzymes onto a food source, partially dissolving it to make the necessary organic or inorganic nutrients available. Some parasitic types obtain their food directly from the cells of a living food source. Some types of fungi are involved in symbiotic relationships, for example, lichens lichen (lī`kən), usually slow-growing organism of simple structure, composed of fungi (see Fungi ) and photosynthetic green algae or
..... Click the link for more information. (a combination of a fungus and a green alga algae (ăl`jē) [plural of Lat. alga=seaweed], a large and diverse group of primarily aquatic plantlike organisms.
..... Click the link for more information. or a cyanobacterium cyanobacteria (sī'ənōbăktĭr`ēə, sī-ăn'ō–) or blue-green algae,
..... Click the link for more information. ) and the mycorrhizae (symbiosis between a fungus and the roots of a vascular plant).

Some fungi are pathogenic to humans and other animals. Such diseases are called mycoses or fungal infections fungal infection, infection caused by a fungus (see Fungi ), some affecting animals, others plants.

Fungal Infections of Human and Animals

Many fungal infections, or mycoses, of humans and animals affect only the outer layers of skin, and although
..... Click the link for more information. . Some molds, in particular, release toxic chemicals called mycotoxins that can result in poisoning or death. Various fungi can also cause serious damage to fruit harvests and other crops (see diseases of plants diseases of plants. Most plant diseases are caused by fungi, bacteria, and viruses. Although the term disease is usually used only for the destruction of live plants, the action of dry rot and the rotting of harvested crops in storage or transport is similar
..... Click the link for more information. ).

Types of Fungi

The 100,000 identified species of organisms commonly classed together as fungi are customarily divided into four phyla, or divisions: Zygomycota, Ascomycota, Basidiomycota, and Deuteromycota.

Zygomycota includes black bread mold mold, name for certain multicellular organisms of the various classes of the kingdom Fungi , characteristically having bodies composed of a cottony mycelium. The colors of molds are caused by the spores, which are borne on the mycelium.
..... Click the link for more information. and molds, such as those of the genus Glomus, that form important symbiotic relationships with plants. 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 from the fusion of neighboring gametangia. There is no distinguishable male or female.

Ascomycota includes yeasts yeast, name applied specifically to a certain group of microscopic fungi and to commercial products consisting of masses of dried yeast cells or of yeast mixed with a starchy material and pressed into yeast cakes.
..... Click the link for more information. , the powdery mildews, the black and blue-green molds, edible types such as the morel and the truffle truffle (trŭf`əl) [Fr.
..... Click the link for more information. , and species that cause such diseases of plants as Dutch elm disease, chestnut blight, apple scab, and ergot ergot (ûr`gət), disease of rye and other cereals caused by the fungus Claviceps purpurea.
..... Click the link for more information. . There are over 50,000 species, about 25,000 of which occur only in lichens. In ascomycetes, the hyphae are subdivided by porous walls through which the cytoplasm and the nuclei can pass. Their life cycle is a complex combination of sexual and asexual reproduction.

Basidiomycota includes the gill fungi (most mushrooms mushroom, type of basidium fungus characterized by spore-bearing gills on the underside of the umbrella- or cone-shaped cap. The name toadstool is popularly reserved for inedible or poisonous mushrooms, but this classification has no scientific basis.
..... Click the link for more information. ), the pore fungi (e.g., the bracket fungi, which grow shelflike on trees, and an edible type called tuckahoe), and the puffballs puffball or smokeball, fungus in which the aboveground portion is typically a stemless brownish sac with an opening at the top through which issues the dustlike mass of ripe spores. The common puffball is Lycoperdon gemmatum.
..... Click the link for more information. . It also includes the fungi that cause smut smut, name for an order of parasitic fungi (Ustilaginales) and the various diseases of plants caused by them. Smuts produce sootlike masses of spores on the host.
..... Click the link for more information. and rust rust, in botany, name for various parasitic fungi of the order Uredinales and for the diseases of plants that they cause. Rusts form reddish patches of spores on the host plant. About 7,000 species are known.
..... Click the link for more information. in plants. Like ascomycetes, the hyphae are subdivided by porous walls. In basidiomycetes, two hyphae fuse to form a dikaryotic mycelium (a mycelium in which both nuclei remain distinct). These mycelia differentiate into reproductive structures called basidia that make up the basidiocarp (the body popularly known as the mushroom cap). The nuclei then fuse and undergo meiosis, creating spores with one nucleus each. When these spores germinate, they produce hyphae, and the process begins again.

Deuteromycota comprises a miscellaneous assortment of fungi that do not not fit neatly in other divisions; they have in common an apparent lack of sexual reproductive features. Also called Fungi Imperfecti, the group includes species that help create Roquefort and Camembert cheeses, that cause diseases of plants and of animals (e.g., athlete's foot and ringworm ringworm or tinea (tĭn`ēə), superficial eruption of the skin caused by a fungus, chiefly
..... Click the link for more information. ), 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.

Usefulness of Fungi

Fungi are valuable economically as a source of antibiotics, of vitamins, and of various industrially important chemicals, such as alcohols, acetone, and enzymes, as well as for their role in fermentation processes, as in the production of alcoholic beverages, vinegar, cheese, and bread dough. They are extremely important in soil renewal, through the decomposition of organic matter (see humus humus (hy
..... Click the link for more information. )—a function unwelcome when it results in the rotting of clothing and other goods and the spoilage of foods.

Bibliography

See C. M. Christensen, The Molds and Man (3d. rev. ed. 1965); J. Webster, Introduction to Fungi (1980); B. Kendrick, The Fifth Kingdom (1985); A. Chandra, Elsevier's Dictionary of Edible Mushrooms (1989); C. T. Ingold and H. J. Hudson, The Biology of Fungi (6th ed. 1993); G. W. Hudler, Magical Mushrooms, Mischievous Molds (1998).