mushroom

The mushroom Amanita muscaria, commonly known as "fly agaric"

A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its 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 those fungi (Basidiomycota, Agaricomycetes) that have a stem (stipe), a cap (pileus), and gills (lamellae, sing. lamella) or pores on the underside of the cap.

"Mushroom" describes a variety of gilled fungi, with or without stems, and the term is used even more generally, to describe both the fleshy fruiting bodies of some Ascomycota and the woody or leathery fruiting bodies of some Basidiomycota, depending upon the context of the word.

Forms deviating from the standard morphology usually have more specific names, such as "puffball", "stinkhorn", and "morel", and gilled mushrooms themselves are often called "agarics" in reference to their similarity to Agaricus or their place Agaricales. By extension, the term "mushroom" can also designate the entire fungus when in culture; the thallus (called a mycelium) of species forming the fruiting bodies called mushrooms; or the species itself.

Identification

Morphological characteristics of the caps of mushrooms

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 basidia and 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 overnight, a powdery impression reflecting the shape of the gills (or pores, or spines, etc.) is formed (when the fruit body is sporulating). The color of the powdery print, called a spore print, is used to help classify mushrooms and can help to identify them. Spore print colors include white (most common), brown, black, purple-brown, pink, yellow, and cream, but almost never blue, green, or red.^[1]

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 medieval times and the Victorian era, combined with microscopic examination. The presence of juices upon breaking, bruising reactions, odors, tastes, shades of color, habitat, habit, and season are all considered by both amateur and professional mycologists. Tasting and smelling mushrooms carries its own hazards because of poisons and allergens. Chemical tests are also used for some genera.^[2]

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 characteristics 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

Trametes versicolor, a polypore mushroom

Typical mushrooms are the fruit bodies of members of the order Agaricales, whose type genus is Agaricus and type species is the field mushroom, Agaricus campestris. However, in modern molecularly-defined classifications, not all members of the order Agaricales produce mushroom fruit bodies, and many other gilled fungi, collectively called mushrooms, occur in other orders of 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 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.^[3]

Other mushrooms are not gilled and then the term "mushroom" is loosely used, so it is difficult to give a full account of their classifications. Some 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. Thus, the term 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.^[4]

Toadstools

Amanita muscaria, the most easily recognised "toadstool", is frequently depicted in fairy stories and on greeting cards. It is often associated with gnomes.^[5]

The terms "mushroom" and "toadstool" 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. Between 1400 and 1600 AD, the terms tadstoles, frogstooles, frogge stoles, tadstooles, tode stoles, toodys hatte, paddockstool, puddockstool, paddocstol, toadstoole, and paddockstooles sometimes were used synonymously with mushrom, mushrum, muscheron, mousheroms, mussheron, or musserouns.^[6]

The word has apparent analogies in Dutch padde(n)stoel (toad-stool/chair, mushroom) and German Krötenschwamm (toad-fungus, alt. word for panther cap). Others have proposed a connection with German "Todesstuhl" (lit. "death's chair").^[7] Since Tod is a direct cognate to death, in that case it would be a German borrowing. However, there is no common word akin to "Todesstuhl" used in German referring to mushrooms, poisonous or not.

In German folklore and old fairy tales there are many depictions of toads sitting on Toadstool mushrooms and catching, with their tongues, the flies that are said to be drawn to the "Fliegenpilz". ("Fliegenpilz" being a German name for the Toadstool, meaning "Flies' mushroom") This is how the mushroom got another of its names, "Krötenstuhl" (a less used German name for the mushroom.), literally translating to "toad-stool"

The term "mushroom" and its variations may have been derived from the French word mousseron in reference to moss (mousse). The toadstool's connection to toads may be direct, in reference to some species of poisonous toad,^[8] or may just be a case of phono-semantic matching from the German word.^[9] However, there is no clear-cut delineation between edible and poisonous fungi, so that a "mushroom" may be edible, poisonous, or unpalatable. The term "toadstool" is nowadays used in storytelling when referring to poisonous or suspect mushrooms. The classic example of a toadstool is Amanita muscaria.

Cultural or social phobias of mushrooms and fungi may be related. The term fungophobia was coined by William Delisle Hay of England who noted a national superstition or fear of "toadstools."^[10][11] He described the "fungus-hunter" as being contemptible and detailed the larger demographic's attitude toward mushrooms as "abnormal, worthless, or inexplicable."^[11] Fungophobia spread to the United States and Australia where it was inherited from England.^[11][12] The underlying cause of a cultural fungaphobia may also be related to the exaggerated importance placed on the few deadly and poisonous mushrooms found in the region of that culture.^[13]

Morphology

Amanita jacksonii buttons emerging from their universal veils

An image of the gills of Lactarius indigo.

A mushroom develops from a nodule, or pinhead, less than two millimeters in diameter, called a primordium, which is typically found on or near the surface of the substrate. It is formed within the mycelium, the mass of threadlike hyphae that make up the fungus. The primordium enlarges into a roundish structure of interwoven hyphae roughly resembling an egg, called a "button". The button has a cottony roll of mycelium, the universal veil, that surrounds the developing fruit body. As the egg expands, the universal veil ruptures and may remain as a cup, or volva, at the base of the stalk, or as warts or volval patches on the cap. Many mushrooms lack a universal veil and therefore do not have either a volva or volval patches. Often there is a second layer of tissue, the partial veil, covering the bladelike gills that bear spores. As the cap expands, the veil breaks, and remnants of the partial veil may remain as a ring, or annulus, around the middle of the stalk or as fragments hanging from the margin of the cap. The ring may be skirt-like as in some species of Amanita, collar-like as in many species of Lepiota, or merely the faint remnants of a cortina (a partial veil composed of filaments resembling a spiderweb), which is typical of the genus Cortinarius. Mushrooms that lack a partial veil do not form an annulus.^[14]

The stalk (also called the stipe, or stem) may be central and support the cap in the middle, or it may be off-center and/or lateral, as in species of Pleurotus and Panus. In other mushrooms, a stalk may be absent, as in the polypores that form shelf-like brackets. Puffballs lack a stalk but may have a supporting base. Other mushrooms, like truffles, jellies, earthstars, bird's nests, usually do not have stalks, and a specialized mycological vocabulary exists to describe their parts.

The way that gills attach to the top of the stalk is an important feature of mushroom morphology. Mushrooms in the genera Agaricus, Amanita, Lepiota and Pluteus, among others, have free gills that do not extend to the top of the stalk. Others have decurrent gills that extend down the stalk, as in the genera Omphalotus and Pleurotus. There are a great number of variations between the extremes of free and decurrent, collectively called attached gills. Finer distinctions are often made to distinguish the types of attached gills: adnate gills, which adjoin squarely to the stalk; notched gills, which are notched where they join the top of the stalk; adnexed gills, which curve upward to meet the stalk, and so on. These distinctions between attached gills are sometimes difficult to interpret, since gill attachment may change as the mushroom matures, or with different environmental conditions.^[15]

Microscopic features

Morchella elata asci viewed with phase contrast microscopy

A hymenium is a layer of microscopic spore-bearing cells that covers the surface of gills. In the non-gilled mushrooms, the hymenium lines the inner surfaces of the tubes of boletes and polypores, or covers the teeth of spine fungi and the branches of corals. In the Ascomycota, spores develop within a microscopic elongated, saclike cell called an ascus, which typically contains eight spores. The Discomycetes—which contains the cup, sponge, brain, and some club-like fungi—develop an exposed layer of asci, as on the inner surface of cup fungi or within the pits of morels. The Pyrenomycetes, tiny dark-colored fungi that live on a wide range of substrates including soil, dung, leaf litter, decaying wood, as well as other fungi, produce minute flask-shaped structures called perithecia, within which the asci develop.^[16]

Austroboletus mutabilis spores viewed using electron microscopy

In the Basidiomycetes, usually four spores develop on the tips of thin projections called sterigmata, which extend from a club-shaped cell called a basidium. The fertile portion of the Gasteromycetes, called a gleba, may become powdery as in the puffballs or slimy as in the stinkhorns. Interspersed among the asci are threadlike sterile cells called paraphyses. Similar structures called cystidia often occur within the hymenium of the Basidiomycota. Many types of cystidia exist and assessing their presence, shape, and size is often used to verify the identification of a mushroom.^[16]

The most important microscopic feature for identification of mushrooms is the spores themselves. Their color, shape, size, attachment, ornamentation, and reaction to chemical tests often can be the crux of an identification. Spores often have a protrusion at one end, called an apiculus, which is the point of attachment to the basidium, termed the apical germ pore, from which the hypha emerges when the spore germinates.^[16]

Growth

Mushroom popping up through macadam in summer near Paris

Many species of mushrooms seemingly appear overnight, growing or expanding rapidly. This phenomenon is the source of several common expressions in the English language including "to mushroom" or "mushrooming" (expanding rapidly in size or scope) and "to pop up like a mushroom" (to appear unexpectedly and quickly). In reality all species of mushrooms take several days to form primordial mushroom fruit bodies, though they do expand rapidly by the absorption of fluids.

The cultivated mushroom as well as the common field mushroom initially form a minute fruiting body, 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 disappear by late afternoon on a hot day after rainfall.^[17] The primordia form at ground level in lawns in humid spaces under the thatch and after heavy rainfall or in dewy conditions balloon to full size in a few hours, release spores, and then collapse. They "mushroom" to full size.

Not all mushrooms expand overnight; some grow very slowly and add tissue to their fruitbodies by growing from the edges of the colony or by inserting hyphae. For example Pleurotus nebrodensis grows slowly, and because of this combined with human collection, it is now critically endangered.^[18]

Yellow, flower pot mushrooms (Leucocoprinus birnbaumii) at various states of development

Though mushroom fruiting bodies are short-lived, the underlying mycelium can itself be long-lived and massive. A colony of Armillaria solidipes (formerly known as Armillaria ostoyae) in Malheur National Forest in the United States is estimated to be 2,400 years old, possibly older, and spans an estimated 2,200 acres (8.9 km²). Most of the fungus is underground and in decaying wood or dying tree roots in the form of white mycelia combined with black shoelace-like rhizomorphs that bridge colonized separated woody substrates.^[19]

Nutrition

Mushrooms are a low-calorie food usually eaten raw or cooked to provide garnish to a meal. Raw dietary mushrooms are a good source of B vitamins, such as riboflavin, niacin and pantothenic acid, and the essential minerals, selenium, copper and potassium. Fat, carbohydrate and calorie content are low, with absence of vitamin C and sodium (table, right).

When exposed to ultraviolet light, natural ergosterols in mushrooms produce vitamin D2,^[20] a process now exploited for the functional food retail market.

Human use

The Agaricus bisporus, one of the most widely cultivated and popular mushrooms in the world

Edible mushrooms

Known as the meat of the vegetable world,^[21] edible mushrooms are used extensively in cooking, in many cuisines (notably Chinese, Korean, European, and Japanese).

Most mushrooms that are sold in supermarkets have been commercially grown on mushroom farms. The most popular of these, Agaricus bisporus, is considered safe for most people to eat because it is grown in controlled, sterilized environments. Several varieties of A. bisporus are grown commercially, including whites, crimini, and portobello. Other cultivated species now available at many grocers include shiitake, maitake or hen-of-the-woods, oyster, and enoki. In recent years increasing affluence in developing countries has led to a considerable growth in interest in mushroom cultivation, which is now seen as a potentially important economic activity for small farmers.^[22]

Mushroom and Truffle output in 2005

There are a number of species of mushroom that are poisonous and, although some resemble certain edible species, consuming them could be fatal. Eating mushrooms gathered in the wild is 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. A. bisporus contains carcinogens called hydrazines, the most abundant of which is agaritine. However, the carcinogens are destroyed by moderate heat when cooking.^[23]

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 can be identified, nor one by which all edible mushrooms can be identified. Additionally, even edible mushrooms may produce an allergic reaction in susceptible individuals, from a mild asthmatic response to severe anaphylactic shock.^[24][25]

People who collect mushrooms for consumption are known as mycophagists,^[26] and the act of collecting them for such is known as mushroom hunting, or simply "mushrooming".

China is the world's largest edible mushroom producer.^[27] The country produces about half of all cultivated mushrooms, and around 2.7 kilograms (6.0 lb) of mushrooms are consumed per person per year by over a billion people.^[28]

Toxic mushrooms

Young Amanita phalloides, "death cap" mushrooms

Many mushroom species produce secondary metabolites that can be toxic, mind-altering, antibiotic, antiviral, or bioluminescent. Although there are only a small number of deadly species, several others can cause particularly severe and unpleasant symptoms. 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 the meal (see emetics), or to learn to avoid consumption altogether. In addition, due to the ability of mushrooms to absorb heavy metals, including those that are radioactive, European mushrooms may, to date, include toxicity from the 1986 Chernobyl disaster and continue to be studied.^{[29][30][31][32][33]}

Psychoactive mushrooms

Hallucinogenic Psilocybe mushrooms

Mushrooms that have psychoactive properties have long played a role in various native medicine traditions in cultures all around the world. They have been used as sacrament in rituals aimed at mental and physical healing, and to facilitate visionary states. One such ritual is the velada ceremony. A practitioner of traditional mushroom use is the shaman and curandera (priest-healer).^[34]

Psilocybin mushrooms possess psychedelic properties. Commonly known as "magic mushrooms" or "shrooms," they are openly available in smart shops in many parts of the world, or on the black market in those countries that have outlawed their sale. Psilocybin mushrooms have been reported as facilitating profound and life-changing insights often described as mystical experiences. Recent scientific work has supported these claims, as well as the long-lasting effects of such induced spiritual experiences.^[35]

Psilocybin, a naturally occurring chemical in certain psychedelic mushrooms like Psilocybe cubensis, is being studied for its ability to help people suffering from psychological disorders, such as obsessive-compulsive disorder. Minute amounts have been reported to stop cluster and migraine headaches.^[36] A double-blind study, done by the Johns Hopkins Hospital, showed that psychedelic mushrooms could provide people an experience with substantial personal meaning and spiritual significance. In the study, one third of the subjects reported that ingestion of psychedelic mushrooms was the single most spiritually significant event of their lives. Over two-thirds reported it among their five most meaningful and spiritually significant events. On the other hand, one-third of the subjects reported extreme anxiety. However, the anxiety went away after a short period of time.^[37][38]

Amanita muscaria pictured above is also psychoactive. The active constituents are ibotenic acid and muscimol. The muscarine-containing chemotaxonomic group of Amanitas contain no amatoxins or phallotoxins, and are not hepatoxic.

Medicinal mushrooms

Ganoderma lucidum

Medicinal mushrooms are mushrooms or extracts from mushrooms that are used or studied as possible treatments for diseases. Some mushroom materials, including polysaccharides, glycoproteins and proteoglycans, modulate immune system responses and inhibit tumor growth. Some medicinal mushroom isolates that have been identified also show cardiovascular, antiviral, antibacterial, antiparasitic, anti-inflammatory, and antidiabetic properties. Currently, several extracts have widespread use in Japan, Korea and China, as adjuncts to radiation treatments and chemotherapy.^[39][40]

Historically, mushrooms have long had medicinal uses, especially in traditional Chinese medicine. Mushrooms have been a subject of modern medical research since the 1960s, where most modern medical studies concern the use of mushroom extracts, rather than whole mushrooms. Only a few specific mushroom extracts have been extensively tested for efficacy. Polysaccharide-K and lentinan are among the mushroom extracts with the firmest evidence. The available results for most other extracts are based on in vitro data, effects on isolated cells in a lab dish, animal models like mice, or underpowered clinical human trials.^[40] Studies show that glucan-containing mushroom extracts primarily change the function of the innate and adaptive immune systems, functioning as bioresponse modulators, rather than by directly killing bacteria, viruses, or cancer cells as cytocidal agents.^[40] In some countries, extracts like polysaccharide-K, schizophyllan, polysaccharide peptide, and lentinan are government-registered adjuvant cancer therapies.^[39][41]

Other uses

"Tinder fungus", species Fomes fomentarius

Mushrooms can be used for dyeing wool and other natural fibers. The chromophores of mushroom dyes 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 mushrooms were the source of many textile dyes.^[42]

Some fungi, types of polypores loosely called mushrooms, have been used as fire starters (known as tinder fungi).

Mushrooms are currently being employed by Ecovative Design LLC to make biodegradable packaging that can directly replace petroleum-based expanded polystyrene packaging.

Mushrooms and other fungi play a role in the development of new biological remediation techniques (e.g., using mycorrhizae to spur plant growth) and filtration technologies (e.g. using fungi to lower bacteria levels in contaminated water). The US Patent and Trademark Office can be searched for patents related to the latest developments in mycoremediation and mycofiltration.

References

Literature cited

• Ammirati JF, Traquair JA, Horgen PA. (1985). Poisonous Mushrooms of Canada: Including other Inedible Fungi. Markham, Ontario: Fitzhenry & Whiteside in cooperation with Agriculture Canada and the Canadian Government Publishing Centre, Supply and Services Canada. ISBN 0-88902-977-6. 
• Hall IR, Stephenson SL, Buchanan PK, Yun W, Cole ALJ. (2003). Edible and Poisonous Mushrooms of the World. Portland, Oregon: Timber Press. ISBN 0-88192-586-1. 
• Stuntz DE, Largent DL, Thiers HD, Johnson DJ, Watling R. (1978). How to Identify Mushrooms to Genus I. Eureka, California: Mad River Press. ISBN 0-916422-00-3. 

External links

Look up mushroom in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Mushrooms

Wikibooks Cookbook has a recipe/module on Mushroom

Wikisource has the text of the 1911 Encyclopædia Britannica article Mushroom.

Identification

• Mushroom Observer (mushroomobserver.org), a collaborative mushroom recording and identification project
• An Aid to Mushroom Identification, Simon's Rock College
• Online Edible Wild Mushroom Field Guide
• List of field guides to mushrooms, from the International

Field Guides database

• search engine for mushrooms identification/determination & identification of other live things in nature

Research associations

• North American Mycological Association
• International Society for Mushroom Science
• Pacific Northwest Fungi Online Journal