Fungus

Template:Taxobox begin Template:Taxobox image Template:Taxobox begin placement Template:Taxobox domain entry Template:Taxobox regnum entry
L., 1753 Template:Taxobox end placement Template:Taxobox section subdivision Chytridiomycota
Zygomycota
Glomeromycota
Ascomycota
Basidiomycota Template:Taxobox end

File:K 1033CR08-9 Yellow fungus on stalk.jpg

Yellow fungus

Fungus growing on a tree in Borneo

For the fictional character, see Fungus the Bogeyman.

A fungus (plural fungi) is a eukaryotic organism that digests its food externally and absorbs the nutrient molecules into its cells. Fungi are very important economically as yeasts in beer and bread, and to the mushroom farming industry. They are the primary decomposers of most forests, and of our old bread as mold. However, the complex biology of fungus extends beyond this common knowlege experience of it.

Phylogeny of fungus

Originally classified as plants, fungi are not true plants because they are heterotrophs (they do not fix their own carbon through photosynthesis but use the carbon fixed by other organisms.) Fungi are more closely related to animals, but unlike animals they are saprotrophic (they absorb their food rather than ingest it) and their cells have cell walls surrounding them. For these reasons, these organisms are now placed in their own kingdom, Fungi. The Fungi are one monophyletic group, meaning all varieties of fungi come from a common ancestor.

Overview

Although often inconspicuous, fungi occur in every environment on earth and play very important roles in most ecosystems. Some fungi are major decomposers of dead plant and animal matter in forests and many other environments. Some types of fungi are parasites on plants and animals, including humans. They are responsible for numerous diseases, such as athlete’s foot and ringworm in humans and Dutch elm disease in plants. Other fungi are partners in symbiotic relationships with other organisms. For example, lichens are formed by a symbiotic relationship between algae or cyanobacteria and fungi. Most vascular plants benefit from a symbiosis between their roots and 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. Of course, many species of mushrooms are poisonous and are responsible for a numerous cases of sickness and death every year. A type of fungus called yeast is used in baking bread and fermenting alcoholic beverages. Fungi are also used to produce industrial chemicals like lactic acid, and even to make stonewashed jeans. Some types of fungi are ingested for their hallucinogenic properties, both recreationally and religiously (as entheogens).

Types of Fungi

The major groups of fungi are mainly classified based on their reproductive structures, such as the types of spores they produce. Currently, there are five divisions (or phyla recognized by mycologists (scientists who study fungi):

• The Chytridiomycota are commonly known as chytrids. These fungi produce zoospores that are capable of moving on their own through the use of flagella.
• The Zygomycota are known as zygomycetes and produce sexual spores called zygospores. Black bread mold is a common species that belongs to this group.
• Members of the Glomeromycota are also known as the arbuscular mycorrhizal fungi. Only one species has been observed forming zygospores, but all other species only reproduce asexually.
• The Ascomycota, commonly known as sac fungi or ascomycetes, produce spores called ascospores, which are enclosed in a special sac-like structure called an ascus. This division includes morel mushrooms and truffles, as well as single-celled yeasts and many species that have only been observed undergoing asexual reproduction.
• Members of the Basidiomycota, commonly known as the club fungi or basidiomycetes, produce spores called basidiospores on club-like stalks called basidia. Most mushrooms belong to this group.

Although the water molds and slime molds have traditionally been placed in kingdom Fungi and are still studied by mycologists, they are not true fungi. Unlike true fungi, the water molds and slime molds do not have cell walls made of chitin. They are currently placed in kingdom Protista.

Structure

Fungi may be single-celled or multicellular. Multicellular fungi are composed networks of long hollow tubes called hyphae. The hyphae often aggregate in a dense network known as mycelium. The mycelium grows through the substrate on which the fungus feeds. Because fungi are imbedded 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. "Mushroom" is the common name given to the above-ground fruiting bodies of many fungal species. Although these above-ground structures are the most conspicuous to humans, they make up only a small portion of the entire fungal body.

The largest organism in the world is purported to be a single Armillaria ostoyae individual growing in a forest in eastern Oregon, USA. The underground mycelial network may cover as much as 890 ha (2200 acres).

Reproduction

Fungi may reproduce sexually or asexually. In asexual reproduction, the offspring are genetically identical to the “parent” organism. During sexual reproduction, a mixing of genetic material occurs so that the offspring exhibit traits of both parents. Many species can use both strategies at different times, while others are apparently strictly sexual or strictly asexual.

Yeasts and other unicellular fungi can reproduce simply by budding, or “pinching off” a new cell. Many multicellular species produce a variety of different asexual spores that are easily dispersed and resistant to harsh environmental conditions. When the conditions are right, these spores will germinate and colonize new habitats.

Sexual reproduction in fungi is somewhat different from that of animals or plants.

Edible and Poisonous Fungi

Some of the most well-known types of fungi are the edible and poisonous mushrooms. Many species are commercially raised, but others must be harvested from the wild. Button mushrooms (Agaricus bisporus) are the most commonly eaten species, used in salads, soups, and many other dishes. Portobello mushrooms are also members of this species, but grow to a much larger size. Other commercially-grown mushrooms that have gained in popularity in the West and are often available fresh in grocery stores include oyster mushrooms, shiitakes, and enoki mushrooms.

There are many more mushroom species that are harvested from the wild for personal consumption or commercial sale. Morels, chanterelles, truffles, black trumpets, and porcini mushrooms (also known as king boletes) all command a high price on the market. They are often used in gourmet dishes.

Hundreds of mushroom species are toxic to humans, causing anything from upset stomachs to hallucinations to death. Some of the most deadly belong to the genus Amanita, including A. virosa (the "Destroying Angel") and A. phalloides (the "Death Cap"). Stomach cramps, vomiting, and diarrhea usually occur within 6-24 hours after ingestion of these mushrooms, followed by a brief period of remission (usually 1-2 days). Patients often fail to present themselves for treatment at this time, assuming that they have recovered. However, within 2-4 weeks liver and kidney failure leads to death if untreated. There is no antidote for the toxins in these mushrooms, but kidney dialysis and administration of corticosteroids may help. In severe cases, a liver transplant may be necessary (Kaminstein 2002).

Fly agaric mushrooms (A. muscaria) are also responsible for a large number of poisonings, but these cases rarely result in death. The most common symptoms are nausea and vomiting, drowsiness, and hallucinations. In fact, this species is used ritually and recreationally for its hallucinogenic properties.

References

• Kaminstein, D. 2002. "Mushroom poisoning". Last accessed 9 November 2005.

External links

• British Mycological Society
• The Fifth Kingdom
• Mycological Society of America
• MykoWeb
• North American Mycological Society