A mushroom is an above-ground fruiting body (that is, a spore-producing structure) of a fungus having a shaft and a cap. By extension, mushroom also designates the entire fungus producing the fruiting body of such appearance, the fungus consisting of a network (called the mycelium) of filaments or hyphae. In an even broader sense, mushroom is applied to any visible fungus, or especially the fruiting body of any fungus, with the mycelium usually hidden under bark, ground, rotten wood, leaves, and other surface matter.
The term toadstool dates from the fourteenth century and is a fanciful name combining toad, which is associated with poison, and stool, which is an archaic term for the head of a fungus.
Strictly speaking, the basidiocarp is the spore-producing structure of a "true" mushroom, while a toadstool is a basidiocarp that is poisonous to eat.
Identifying mushrooms requires a basic understanding of their macroscopic structure. A "typical" mushroom consists of a cap or pileus supported on a stem or stipe. Both can have a variety of shapes and be ornamented in various ways. The underside of the cap (in agarics) is fitted with gills or lamellae where the actual spores are produced. How the gills are attached is another important characteristic used in identification. In the boletes, the gills are replaced by small openings called pores. Bracket fungi essentially lack a stipe, and the cap is attached like a bracket to the substratum, usually a log or tree trunk. Some bracket fungi have gills, others have pores.
The main types of mushrooms are agarics (the button mushroom, the most common mushroom eaten in many western countries), boletes, chanterelles, tooth fungi, polypores, puffballs, jelly fungi, coral fungi, bracket fungi, stinkhorns, and cup fungi. Mushrooms and other fungi are studied by mycologists. The "true" mushrooms are classified as Basidiomycota. A few mushrooms are classified by mycologists as Ascomycota, the morel and truffle being good examples. 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; however, there is an estimated 1.5 million species of fungi, of which it is likely there are about 140,000 of species qualifying as mushrooms.
In general, identification to genus can 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 young bud into a mature structure and only the latter can provide certain identification of the species. Examination of mature spores, or at least knowing their color, is often essential. To this end, a common method used to assist in identification is the spore print.
Edible mushrooms are used extensively in cooking, in many cuisines (notably Chinese, European and Japanese). Though commonly thought to contain little nutritional value, many varieties of mushrooms are high in fiber and protein, 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. However, a number of species of mushrooms are poisonous, and although some may resemble edible varieties, eating them could be fatal. Eating mushrooms gathered in the wild can be risky and a practice not to be undertaken by individuals not knowledgeable in mushroom identification. The problem is that separating edible from poisonous species depends upon the application of only a few easily recognizable traits. 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".
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.
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. 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 effect 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, curandera (priest-healer), Maria Sabina.
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 headaches.
Mushrooms can be also 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 mushrooms have been used as fire starters (known as tinder fungi). Ötzi the Iceman was found carrying such mushrooms. 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 office can be searched for patents related to the latest developments in mycoremediation and mycofiltration.