Mushrooms

Categories: Economic botany and plant uses; food; fungi; poisonous, toxic, and invasive plants

Fossil evidence suggests that mushrooms existed ninety million years ago. The order Agaricales represents approximately four thousand species in sixteen families of commonly found mushrooms. The order Polyporus consists of fungi that grow on tree limbs or stumps. Although they prefer moist environments, mushrooms are sometimes found in deserts, beaches, and occasionally snowdrifts.

Characteristics

The mushrooms familiar to most people are hymenomycetes. They are either edible or poisonous structures lacking chlorophyll. That is, like other fungi, they do not make their own food through photosynthesis but instead are heterotrophs, which feed off other organisms. They are classified as thousands of species, distributed globally. Most mushrooms consist of a fleshy fruiting body called the sporophore and a cylindrical stalk.

Most mushrooms with the familiar umbrella-shaped sporophore, called the cap or pileus, belong to the family Agaricaceae. The pileus has narrow sheets called gills that contain the spores. The pileus sits atop the stalk, known as the stipe. Pilei and stipes vary in size.

Sporophores grow from a mat of thin strands called the mycelium, or spawn, which is located below the soil surface. Each mycelium grows new sporophores during the annual fruiting season. Mycelial life spans range from several months to centuries, depending on nutrient and moisture sources and suitable temperature. A honey mushroom mycelium in Michigan once spread across 40 acres over fifteen hundred years.

Mushrooms grow quickly, often maturing within several days. A membrane joins the cap’s edges to the stem. As mushrooms mature, the membrane breaks, revealing the cap’s gills. When the agaric mushroom ripens, its color changes from white to pink, then brown. Some mushrooms’ colors change when they are exposed to air or water. Mushrooms are geotropic, keeping their caps upright and gills vertical and turning the pileus if placed on their sides after being picked.

Species

Wild mushrooms grow in fields, forests, lawns, and gardens. The waxy caps are among the most colorful mushrooms. In spring, morels emerge, often thriving on burned land. Their gills resemble honeycombs. The genus Gyromitra includes the false morels, which can be toxic.

The family Boletaceae includes mushrooms that contain layers of spores in tubes on the pileus’s undersurface. The Hydnum mushrooms appear to have teeth, and the Clavarias look like coral. Occasionally, sporophores grow in circular patterns popularly called fairy rings.

The Coprinus comatus, or shaggy mane, is another spring mushroom which appears through the fall in open areas, with individuals or groups of this species often reemerging in the same place annually. This mushroom has tall, brown caps that appear shaggy because of soft scales on its surface. Unlike most mushrooms, members of Coprinus have caps that do not expand at maturity, which causes the compacted gills to liquefy into a black fluid, resulting in the collective name for the one hundred species of this genus, “inky caps.”

The species Agaricaceae campestris profusely grows in rural areas, especially during the summer. The orange or yellow funnel-capped Cantherellus cibarius thrives in European forests, tastes nutty, and has been a preferred edible mushroom since the days of the Roman Empire. By autumn, large mushrooms representing the genus Boletus ripen in wooded areas. Veins on caps of Boletus species change color from white to yellow, indicating their readiness for picking.

Several mushroom species live on decaying wood hosts. Rotten timber is the habitat for Polyporus sulfurreus, which form as orange-yellow shelves that can be meters wide and weigh many kilograms. Pores beneath the layers create spores.

Poisonous Mushrooms

Between sixty and seventy mushroom species are poisonous. If consumed, poisonous mushroom species can cause intense physical reactions, ranging from sickness to death. The genus Amanita includes the most dangerous mushrooms, including Amanita muscarine. Only the Amanita caesarea is edible. The fly mushroom, Amanita muscaria, is a large, colorful mushroom that is deadly to insects. The white Amanita phalloides, known as the death cap or death angel, are the most toxic mushrooms and are widely distributed. Other hazardous mushrooms are Boletus satana (Satan’s mushroom) and Clitocybe illudens (jack-o’-lantern), which glows in the dark and is physically similar to the benign Clitocybe gigantea.

Alkaloid mycotoxins in mushrooms attack nerve, muscle, blood, and organ cells. Victims suffer digestive symptoms within eight to twelve hours after ingesting mushrooms, then slip into a coma and die several days later. Patients undergo gastrointestinal tract purging and antidote treatment in an effort to counter poisoning.

Uses

Humans have cultivated mushrooms for thousands of years. Some mushrooms lack flavor or are too bitter or woody to consume. Others, such as Ithyphallus impudicus, have a foul odor. The Pleurotus ostreatus tastes like oysters. Although mushrooms are not especially nutritious because they are 90 percent water, many have pleasing tastes and textures and are low in fat.

Annually, about ten million North Americans hunt common mushrooms, especially morels. The mushroom industry relies on mushrooms picked and sold at wholesale prices totaling millions of dollars. Brokers ship the mushrooms to distributors or retail markets.

Commercial growers produce a safe source of edible mushrooms. These mushrooms are cultivated in specially designed structures, caves, or cellars in which the darkness, humidity, and temperature are regulated. Beds of soil-covered straw and manure are planted with mycelia. The Agaricus bisporus, a hybrid developed by researchers, is the most common commercial species. Exotic wild mushrooms, including portobello and shiitake, are cultivated artificially. Liquid nitrogen is used to store spawns and enhances their endurance and quality. Scientists are genetically designing improved mushroom strains.

Some mushrooms are hallucinogenic, and most governments restrict their use as a narcotic, although mushrooms are smuggled into countries that have bans. Various cultures incorporate mushrooms into spiritual rituals, believing the mushrooms have magical powers. Researchers have determined that some mushrooms, specifically the Gleophyllum odoratum and Clitocybe gibba species, can be therapeutic if thrombin inhibitors are extracted to manufacture anticoagulant pharmaceuticals.

Bibliography

Benjamin, Denis R. Mushrooms: Poisons and Panaceas. New York: W. H. Freeman, 1995. Comments on mushrooms’ medicinal and toxic properties. Includes illustrations, bibliographical references, and index.

Bessette, Alan E., William C. Roody, and Arleen R. Bessette. North American Boletes: A Color Guide to the Fleshy Pored Mushrooms. Syracuse, N.Y.: Syracuse University Press, 2000. Focuses on identification and uses of a specific mushroom family. Includes illustrations, bibliographical references, and indexes.

Fisher, David W., and Alan E. Bessette. Edible Wild Mushrooms of North America. Austin: University of Texas Press, 1992. Guide with recipes for consuming mushrooms. Includes illustrations, bibliographical references, and index.

Phillips, Roger. Mushrooms of North America. Boston: Little, Brown, 1991. Provides details for identification of common and rare edible and poisonous mushrooms. Includes illustrations, bibliographical references, and index.

Schaechter, Elio. In the Company of Mushrooms: A Biologist’s Tale. Cambridge, Mass.: Harvard University Press, 1997. Narrates author’s experiences, supplemented with information about mushroom science, history, and myths. Includes illustrations, bibliographical references, tables, and index.