Human and Ecological Relevance of the Club Fungi

Of the approximately 25,000 described species of club fungi, fewer than 75 are known to be poisonous. Many of the latter are, however, common and not readily distinguishable by amateurs from edible species. Also, some edible forms, such as the inky cap mushrooms, cause no problems by themselves but may make one very ill if consumed with alcohol. Few of the poisonous forms normally are fatal, but

Kingdom Fungi 371

unfortunately, some—such as Amanita spp., which cause 90% of the fatalities attributed to mushroom poisoning—are relatively common.

Poisoning from death angels and similar species is due to alpha-amatin (an alkaloid). The poison completely blocks RNA synthesis, and symptoms of poisoning usually take from 6 to 24 hours to appear. Treatment, which in the United States usually includes pumping of the stomach and ingestion of activated charcoal, is seldom successful by the time the intense stomachache, blurred vision, violent vomiting, and other symptoms occur.

In the late 1950s there were claims that administration of alpha lipoic acid (thioctic acid) in a few instances prevented a fatality, but subsequent research has failed to substantiate the claims. In Europe, injections of silibinin and silymarin (extracts of milk thistle—Silybum marianum) do appear to have been at least partially effective as antidotes. Oral forms of silymarin are available in North America, but they are much less effective than the injectable forms. Injectable silibinin and silymarin have not yet received FDA approval for treatment of mushroom poisoning in the United States. When a small, nonfatal ingestion has occurred, the mushroom poison usually leaves the patient with hypo-glycemia (a blood sugar deficiency), which can be countered with the intravenous administration of glucose. Some wild-mushroom lovers have fed a part of their collection to a dog or cat, and when nothing happened to the animal after an hour or two, they have eaten the mushrooms themselves. Both they and the animals later succumbed. Others have mistakenly believed that the toxic substances are destroyed by cooking. Records show, however, that before the discovery of milk thistle antidotes, death ensued in 50% to 90% of those who had eaten just one or two of the deadly mushrooms, cooked or raw, and that even as little as 1 cubic centimeter (less than a 0.5 cubic inch) can be fatal.

There are many widespread but very unreliable beliefs about distinctions between edible and poisonous mushrooms. Some believe that a silver coin placed in the cooking pan will turn black while the mushrooms are cooking if any poison is present. However, there are both edible and poisonous species that will turn such a coin black, and others will not. Another superstition holds that edible species can be peeled while poisonous ones cannot. Again, this is a fallacy, for Amanita mushrooms peel quite easily. Still other erroneous beliefs maintain that poisonous mushrooms appear only in the fall or the early spring, or that all mushrooms eaten by snails and beetles are edible, or that all purplish-colored mushrooms are poisonous, or that all mushrooms growing in grassy areas are edible. Again, these notions simply are not supported by the facts. Wild mushrooms can be eaten with some confidence only if they have been identified by a knowledgeable authority. It is foolhardy for anyone to do otherwise.

Some poisonous mushrooms cause hallucinations in those who eat them. During the Mayan civilization in Central America, a number of teonanacatl ("God's flesh") sacred mushrooms (Fig. 19.28) were used in religious ceremonies.

The consumption of these mushrooms has continued among native groups in Mexico and Central America to the present. Ingestion of small amounts results in sharply focused, vividly colored visions. Similar use of the striking fly agaric mushroom (Fig. 19.29; see also the chapter-opening photo) in Russia, and for a while in the Indus valley of India, dates back to many centuries B.C. Users appear to go into a state of intoxication. It is believed that the ancient Norwegian beserkers, who occasionally exhibited fits of exceptionally savage behavior, did so after consuming fly agaric mushrooms. Related species that occur in the United States have not produced the same effects but have, instead, caused the

Figure 1Q.2Q Fly agaric mushrooms. (Courtesy Perry J. Reynolds)

Chapter 19

user to become nauseated and to vomit. In Siberia, users have noted that the intoxicating principle is passed out in the urine, and some persons have adopted the practice of drinking the urine of persons who have consumed fly agaric mushrooms. Reindeer, incidentally, are reported to be obsessed with both fly agaric and human urine.

More than 90% of a mushroom is water, and mushrooms generally contain smaller quantities of nutritionally valuable substances than most foods. An apparent exception is the legendary shiitake mushroom, grown for centuries in China and Japan on oak logs and now cultured in the United States. It has more than double the protein of ordinary, commercially grown mushrooms and is very rich in calcium, phosphorus, and iron. It has excellent flavor and also contains significant amounts of B vitamins, vitamin D2 (ergos-terol), and vitamin C.

Ancient Chinese royalty believed that eating shiitake mushrooms would promote healthful vigor and retard the aging process, but no extensive research either supporting or refuting the claims has yet been conducted.

Lentinacin, an agent capable of lowering human cholesterol levels, has been obtained from shiitake mushrooms, and purified extracts from spores of the mushrooms have demonstrated antiviral activity against influenza and polio viruses in laboratory animals.

Since ancient times, many types of mushrooms have been cultivated for food. In the 2d century B.C., a Greek doctor by the name of Nicandros taught people how to grow mushrooms underneath fig trees on soil fertilized with manure. Andrea Cesalpino, a noted Italian botanist and physician of the 16th century, cultivated mushrooms by scattering pulverized poplar bark on very rich soil near poplar trees with which the mushrooms were associated. In more recent times, Italians have cultivated mushrooms on waste material from olives, on coffee grounds, on remnants of oak leaves after tannins have been extracted for leather tanning, and on laurel berries. Today, jelly fungi and various mushrooms are cultivated in the Orient on media composed of wood and manure.

In Geneva, Switzerland, there is a special market for wild mushrooms where more than 50 species are sold under the supervision of a state mycologist. Although wild mushrooms are consumed by many in North America, fewer such species are sold in markets. Only one species of mushroom (Agaricus bisporus—portabella mushroom) is extensively cultivated commercially, although several others such as shiitake and oyster are steadily gaining in popularity. Mushrooms have been grown in basements, caves, and abandoned mines, but contrary to widespread belief, light does not at all affect their growth.

Large-scale mushroom-growing operations generally use windowless warehouses with stacked rows of shallow planting beds because temperatures, humidity, and other climatic factors are easier to control in such buildings (Fig. 19.30). The mushrooms are grown on compost made from straw and horse or chicken manure. Prior to use, the com-

Mushroom Commercial Shed
Figure 1Q.30 Mushroom beds in a commercial mushroom farm in Petaluma, California.

post is pasteurized for a week to destroy microorganisms, unwanted fungi, and insects and their eggs. Then it is inoculated with spawn, which is compact mycelium grown from germinated basidiospores sown on bran of wheat or other grains. After inoculation, the spawn is covered with a thin layer of soil. The moisture content of the compost is controlled with regular, light waterings, and a humidity of about 75% is maintained.

The mycelium grows in temperatures ranging from just above freezing to 33°C (91.4°F), but commercial growers try to keep the temperatures between 9°C and 13°C (48°F to 55°F) because the mushrooms are less subject to disease or insect attacks and are also firmer when grown under cool conditions. The mushroom buttons appear within a week to 10 days after spawn is planted and continue appearing for 6 months or more. About 1 kilogram (2.2 pounds) of mushrooms is obtained from each 10 square decimeters (slightly over 1 square foot) of growing area. An estimated 59,000 metric tons (65,000 tons) of mushrooms are produced annually in the United States, and lesser but significant amounts in Canada.

Fungi are constantly breaking down dead wood and debris and returning the components to the soil where they can be recycled. Sometimes, as we have seen, they can be very destructive from a human viewpoint, attacking everything from living plants and harvested or processed food to shoe leather, paper, cloth, construction timbers, paint, petroleum products, upholstery, and even glass, particularly in warmer humid climates.

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