Mushroom
A Mushroom is the fleshy, spore-bearing fruiting body of fungus typically produced above ground on soil or on their food source. The standard for the name mushroom is the cultivated white button mushroom, Agaricus bisporus, hence the word mushroom is most often applied to fungi (Basidiomycota, Agaricomycetes) that have a stem (called a stipe), a cap (called a pileus), and gills (each called a lamella/pl. lamellae) on the underside of the cap just as do store-bought white mushrooms. However, mushrooms can also be a wide variety of gilled fungi, with or without stems, and the term is used even more generally to describe both fleshy fruitbodies of some Ascomycota and woody or leathery fruitbodies of some Basidiomycota, depending upon the context of the usage. Usually forms deviating from the standard form have more specific names, such as puffballs, stinkhorn, morels, etc. and gilled mushrooms themselves are often called agarics, in reference to their similarity to Agaricus or placement in the order Agaricales.  By extension, mushroom can also designate the entire fungus when in culture or when referring to the whole thallus (called a mycelium) of species forming fruitbodies called mushrooms.

# Identification
Identifying mushrooms requires a basic understanding of their macroscopic structure. Most are Basidiomycetes and gilled. Their spores, called basidiospores, are produced on the gills and fall in a fine rain of powder from under the caps as a result. At the microscopic level the basidiospores are shot off of basidia but then fall between the gills in the dead air space. As a result, for most mushrooms, if the cap is cut off and placed gill-side down, usually overnight a powdery impression reflecting the shape of the gills (or pores, or spines, etc.) is formed (when the fruitbody is sporulating). The color of the powdery print (which is called a spore print) has been used to help classify mushrooms, hence is used to help identify them. Spore print colors range from white (most common), brown, black, purple-brown, pink, yellow, cream, and almost never blue, green, or red.
While modern identification of mushrooms is quickly becoming molecular, the standard methods for identification are still used by most and have developed into a fine art harking back to mediaeval times and the Victorian era, combined with microscopic examination. The presence of juices upon breaking, bruising reactions, odors, tastes, shades of colors, and habitats and habit and season must, and are, all considered by mycologists, amateur and professional alike. Tasting and smelling mushrooms carry their own hazards because of poisons and allergens. Chemical spot tests are also used for some genera.
In general, identification to genus can often be accomplished in the field using a local mushroom guide. Identification to species, however, requires more effort; one must remember that a mushroom develops from a button stage into a mature structure and only the latter can provide certain characters needed for the identification of the species. However, over mature specimens lose features and cease producing spores. Many novices have mistaken humid water marks on paper for white spore prints, or discolored paper from oozing liquids on lamella edges for colored spored prints.

# Classification
Typical mushrooms are the fruitbodies of members of the order Agaricales, whose type genus is Agaricus, and type species is the field mushroom, Agaricus campestris. However, in modern molecular defined classifications, not all members of the order Agaricales produce mushroom fruitbodies, and many other gilled fungi, collectively called mushrooms, occur in other orders in the class Agaricomycetes. For example, chanterelles are in the Cantharellales, false chanterelles like Gomphus are in the Gomphales, milk mushrooms (Lactarius) and russulas (Russula) as well as Lentinellus are in the Russulales, while the tough leathery genera Lentinus and Panus are among the Polyporales, but Neolentinus is in the Gloeophyllales, and the little pin-mushroom genus, Rickenella along with similar genera are in the Hymenochaetales.
Within the main body of mushrooms, in the Agaricales, are such common fungi like the common fairy-ring mushroom (Marasmius oreades), shiitake, enoki, oyster mushrooms, fly agarics and other amanitas, magic mushrooms like species of Psilocybe, paddy straw mushrooms, shaggy manes, etc.
An atypical 'mushroom' is the Lobster mushroom, which is a deformed, cooked-lobster-colored parasitized fruitbody of a Russula or Lactarius colored and deformed by the mycoparasitic Ascomycete Hypomyces lactifluorum.
Other 'mushrooms' are nongilled and then the term is loosely used, so that it is difficult to give a full account of their classifications. Some 'mushrooms' have pores underneath (and are usually called boletes), others have spines, such as the hedgehog mushroom and other tooth fungi, and so on. Mushroom has been used for polypores, puffballs, jelly fungi, coral fungi, bracket fungi, stinkhorns, and cup fungi. Mushrooms and other fungi are studied by mycologists. Thus, the term mushroom is more one of common application to macroscopic fungal fruiting bodies than one having precise taxonomic meaning. There are approximately 14,000 described species of mushrooms.

# Mushrooms vs. Toadstools
The terms "mushrooms" and "toadstools" go back centuries, and were never precisely defined, nor was there consensus on application. The term "toadstool" was often but not exclusively, applied to poisonous mushrooms or to those that have the classic umbrella-like cap-and-stem form. For an example of early usage see Badham (1863). Reference was made to "tadstoles", "frogstooles", "frogge stoles", "tadstooles", "tode stoles", "toodys hatte","paddockstool", "puddockstool", "paddocstol", "toadstoole", and "paddockstooles" from 1398-1597, sometimes synonymous with "mushrom", "mushrum", "muscheron", "mousheroms", "mussheron", or "musserouns" .  The term "mushroom" and its variations may have been derived from the French word "Mousseron" in reference to moss (mousse). There may have been a direct connection to toads (in reference to poisonous properties) for toadstools. However, there is no clear-cut delimitation between edible and poisonous fungi, so that mushrooms may be edible, poisonous, or unpalatable, and it makes no sense to not be able to use the term mushroom when stating there are "poisonous mushrooms" which would be an oxymoron if the term mushroom could not be applied to poisonous fungi. The term toadstool is nowadays used in story telling when referring to poisonous or suspect mushrooms, and mycologists avoid the use of the term as it is highly ambiguous. The classic example of a toadstool is Amanita muscaria.

# To mushroom - mushrooming - to pop up like mushrooms
Many species of mushrooms seemingly appear overnight, growing or expanding rapidly. This phenomenon is the source of several commonly used phrases in the English language. In fact all species of mushrooms take several days to form primordial mushroom fruit bodies. The cultivated mushroom as well as the common field mushroom initially form minute fruiting body initials referred to as the pin stage, because of their small size. Slightly expanded they are called buttons, once again because of the relative size and shape. Once such stages are formed, the mushroom can rapidly pull in water from its mycelium and expand, mainly by inflating preformed cells that took several days to form in the primordia. Similarly, there are even more ephemeral mushrooms, like Parasola plicatilis ( formerly Coprinus plicatlis) that literally appear overnight and may be gone by late afternoon on hot summer days after rainfall. The primordia form at ground level in lawns in humid spaces under the thatch of lawns and after heavy rainfall or dewy conditions, balloon to full size in a few hours, release spores, then collapse. They "mushroom" to full size. "To mushroom" means to rapidly grow in size, or to sprout up rapidly, i.e., an organization may "mushroom" from national to international almost overnight.  To "pop up like mushrooms" is of similar derivation, but also has a gang slang usage. The slang term "mushrooms" is a gang related term for victims accidentally shot as collateral damage simply because they popped up suddenly, as do fungal mushrooms.
The term "mushrooming" differs in that it generally refers to the act of gathering mushrooms, in the wild, as in the statement "I'm going mushrooming today." This is often shortened to "shrooming", which has yet another connotation, which is to "do mushrooms". To "do mushrooms" or "shrooms" often refers to taking hallucinogenic mushrooms (see below).
Notably, not all mushrooms expand overnight. Many are very slow growing. Those types of mushrooms generally add tissue to their fruitbodies in different manners, such as growing from the edges, or inserting hyphae.
The largest living thing in the world is a mushroom.
It is known as the honey fungus (Armillaria Ostoyae), and is not particularly a rare mushroom; you may well have one growing on a dead tree stump in your garden.
The largest recorded specimen is in Malheur National Forest Oregon USA. It covers 2,200 acres and is between 2,000 and 8,000 years old. Most of it is underground in the form of white mycelia (the mushroom equivilant of roots).

# Human use

## Edible mushrooms
Edible mushrooms are used extensively in cooking, in many cuisines (notably Chinese, European and Japanese). Though commonly thought to contain little nutritional value, many species of mushrooms are high in fiber, and provide vitamins such as thiamine (B1), riboflavin (B2), niacin (B3), biotin (B7), cobalamins (B12) and ascorbic acid (C), as well as minerals, including iron, selenium, potassium and phosphorus. Mushrooms have been gaining a higher profile for containing antioxidants Ergothioneine and Selenium.
Most mushrooms that are sold in supermarkets have been commercially grown on mushroom farms. The most popular of these, Agaricus bisporus, is safe for most people to eat because it is grown in controlled, sterilized environments, though some individuals do not tolerate it well. Several varieties of A. bisporus are grown commercially, including: whites, crimini and portabello. Other cultivated species now available at many grocers include shiitake, maitake or hen-of-the-woods, oyster and enoki.
There are a number of species of mushrooms that are poisonous, and although some resemble certain edible species, eating them could be fatal. Eating mushrooms gathered in the wild can be risky and should not be undertaken by individuals not knowledgeable in mushroom identification, unless the individuals limit themselves to a relatively small number of good edible species that are visually distinctive. More generally, and particularly with gilled mushrooms, separating edible from poisonous species requires meticulous attention to detail: there is no single trait by which all toxic mushrooms could be identified, nor one by which all edible mushrooms could be identified.
People who collect mushrooms for consumption are known as mycophagists, and the act of collecting them for such is known as mushroom hunting, or simply "mushrooming".

## Toxic mushrooms
Of central interest with respect to chemical properties of mushrooms is the fact that many species produce secondary metabolites that render them toxic, mind-altering, or even bioluminescent. Toxicity likely plays a role in protecting the function of the basidiocarp: the mycelium has expended considerable energy and protoplasmic material to develop a structure to efficiently distribute its spores. One defense against consumption and premature destruction is the evolution of chemicals that render the mushroom inedible, either causing the consumer to vomit (see emetics) the meal or avoid consumption altogether.

## Psychoactive mushrooms
Psilocybin mushrooms possess psychedelic properties. They are commonly known as "magic mushrooms" or "shrooms", and are available in smart shops in many parts of the world, though some countries have outlawed their sale. A number of other mushrooms are eaten for their psychoactive effects, such as fly agaric, which is used for shamanic purposes by tribes in northeast Siberia. They have also been used in the West to potentiate, or increase, religious experiences. Because of their psychoactive properties, some mushrooms have played a role in native medicine, where they have been used to affect mental and physical healing, and to facilitate visionary states. One such ritual is the Velada ceremony. A representative figure of traditional mushroom use is the shaman and curandera (priest-healer) Maria Sabina.

## Medicinal mushrooms
Currently, many species of mushrooms and fungi utilized as folk medicines for thousands of years are under intense study by ethnobotanists and medical researchers. Maitake, shiitake, and reishi are prominent among those being researched for their potential anti-cancer, anti-viral, and/or immunity-enhancement properties. Psilocybin, originally an extract of certain psychedelic mushrooms, is being studied for its ability to help people suffering from mental disease, such as obsessive-compulsive disorder. Minute amounts have been reported to stop cluster and migraine headache .

## Other uses
Mushrooms can be used for dyeing wool and other natural fibers. The chromophores of mushrooms are organic compounds and produce strong and vivid colors, and all colors of the spectrum can be achieved with mushroom dyes. Before the invention of synthetic dyes the mushrooms were the primary sources on dyeing textiles. This technique has survived in Finland, and many Middle Ages re-enactors have revived the skill again.
Some fungi, types of polypores, loosely called mushrooms, have been used as fire starters (known as tinder fungi). Otzi the Iceman was found carrying such fungi.  Mushrooms, and other fungi, will likely play an increasingly important role in the development of effective biological remediation and filtration technologies. The US Patent and Trademark officecan be searched for patents related to the latest developments in mycoremediation and mycofiltration.