The World's Largest Vegetable

4. Tropical Yams Named After Dioscorides

Although rarely seen in North America, true yams (Dioscorea spp., Dioscoreaceae) are the third most important tropical "root" crop after cassava (Manihot esculenta, Euphorbiaceae) and sweet potato (Ipomoea batatas, Convolvulaceae). This is especially true in West Africa, parts of Central America and the Caribbean, the Pacific Islands, and Southeast Asia. Other important starchy "root" crops are taro and dasheen (Colocasia esculenta, Araceae), the source of Polynesian poi, arrowroot (Maranta arundinacea, Marantaceae), and achira (Canna edulis, Cannaceae). The true yam is about 20 percent starch and as a food is very similar to a potato. The generic name commemorates Dioscorides, the ancient Greek physician and naturalist (1st Century AD). Dioscorides authored the classic De Materia Medica, a five volume reference of several thousand plant drugs that was used for 15 centuries. The most commonly cultivated edible yams are D. rotundata and D. cayensis in Africa, D. alata and D. esculenta in Asia, and D. trifida in the New World, although many cultivated varieties are known. They are climbing perennial vines with shiny, heart-shaped leaves, arising from large underground stems that are technically called tubers rather than roots. Like a potato, the tubers can be propagated by planting sections containing the "eyes" or buds; however, harvesting them is a laborious task because the tubers are deeply buried. Dioscorea is a large genus with more than 600 species. An African species called elephant's foot or Hottentot's bread (D. elephantipes) produces a massive basal stem (caudex) weighing up to 700 pounds (318 kg). The above-ground part of this caudex resembles the shell of a tortoise; hence the common name of "turtleback plant." Like other caudiciform xerophytes (desert plants with enlarged basal stems), the vine relies on carbohydrates and moisture stored in its stem during extended periods of drought. During severe drought conditions the gigantic tuberous stems are eaten as famine food by Hottentots. Luckily for the Hottentots, the tuberous stems are thoroughly cooked because they contains toxic saponins that are broken down during the heating process. Although not a common vegetable, this plant would easily take the record of "World's Largest Vegetable." Another unusual African yam is the air potato (Dioscorea bulbifera). It has small or no subterranean tubers, but instead develops large, liver-shaped aerial tubers up to four pounds (2 kg) each. In New Guinea and Melanesia special ceremonial yams weighing over 120 pounds (54 kg) are grown to reflect the grower's status in the community. The yams are used for gifts and ritualized exchanges. A yam festival is held at harvesttime during which the tubers are covered by elaborate woven masks. There are reportedly yams in tropical Asia and the South Pacific that are much larger. In fact, there is one rather dubious, unconfirmed report of an enormous yam on the island of Pohnpei that was 10 feet (3 m) in length and weighed up to 1500 pounds (680 kg). Rumors have it that at least 10 people were required to carry it. REMEMBER THAT THIS RECORD IS UNSUBSTANTIATED AND MAY NOT BE TRUE.

5. Steroids That Foam In Water

In addition to food, the tubers of some Mexican and Central American species of Dioscorea (including D. composita and D. floribunda) are rich in a natural steroid called diosgenin. Natural plant steroids are formed by the polymerization of 5-carbon isoprene subunits into tetracyclic triterpenoid compounds during complex metabolic pathways inside plant cells.

All steroids have the same fundamental structure of four (tetracyclic) carbon rings called the steroid backbone or steroid nucleus. The addition of different chemical groups at different places on this backbone leads to the formation of many different steroidal compounds, including the sex hormones progesterone and testosterone, the anti-inflammatory steroid cortisone, and the cardiac steroids digoxin and digitoxin. The important animal steroid, cholesterol, also has this tetracyclic backbone structure. Some of these compounds are called steroidal glycosides (or glucosides) because they also contain sugar molecules. Steroidal compounds in the Dioscoreaceae, Liliaceae and Agavaceae are also called saponins because they foam in water. In fact, some of these steroidal saponins, such as the soap lily (Chlorogalum pomeridianum, Liliaceae) were used as soap by native Americans. Steroidal saponins may irritate mucous membranes, break down red blood cells in vitro, and are especially toxic to cold-blooded animals. In fact, fresh bulbs were used to paralyze and capture fish by throwing slices of bulbs into ponds and streams, and roasted bulbs were also eaten by several tribes of California Indians. Apparently the saponins are especially toxic to respiratory organs of fish without affecting their edibility. Saponins have also been used in shampoos, foam fire extinguishers, toothpaste, and in the brewing industry as a foaming agent for the froth ("head") of beer. Commercial sources of saponins include the soapberry tree (Sapindus saponaria, Sapindaceae), soapbark tree (Quillaja saponaria, Rosaceae), and the popular bouncing bet (Saponaria officinalis, Caryphyllaceae).

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6. Cardiac Steroids That Stimulate Your Heart

Cardiac glycosides (steroids with attached sugar molecules--including digoxin and digitoxin) from the European foxglove (Digitalis purpurea, Scrophulariaceae) serve as a powerful heart stimulant in humans. They prolong the relaxation phase of the heart (diastole) during which the left ventricle fills with blood. This results in a stronger ventricular contraction (systole) and greater volume of blood pumped out through the aorta. Of course, relaxing the heart so the ventricles have a chance to fill with maximum blood volume can have serious side effects--too much digitalis can cause a permanent relaxation resulting in a "flat-liner" and a one-way trip to the "happy hunting grounds."

Another fascinating story about steroidal glycosides involves the monarch butterfly. Toxic steroidal glycosides are ingested by caterpillars as they feed on milkweed plants of the genus Asclepias (Asclepiadaceae). The glycosides have no ill effects on the ravenous caterpillars and are actually stored in their bodies. Upon metamorphosis the glycosides show up in the bodies of the adult monarch butterfly--thus rendering them toxic to predatory birds. One swallow of such a butterfly is very distasteful or may cause the bird to become gravely ill--and birds quickly learn to avoid monarchs.

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7. Contraception With Yams

Contraception with yams is not based on the "plug and play" principle of a diaphragm (or Windows 95!), it is based on an intricate hormonal feedback system called the menstrual cycle. The discovery of a natural steroidal precursor in tropical yams has greatly reduced the cost of synthetic steroids used in birth control pills and corticosteroids used to treat Addison's disease, asthma, arthritis, bursitis, tendinitis, dermatitis, hemorrhoids, and many other ailments. It is possible to synthesize these hormones from bile acids of cattle or extract them from excised adrenal cortexes, but such methods are time- consuming and very expensive. The most cumbersome part of the chemical synthesis of these hormones is the complex steroidal backbone. At one time it took 40 oxen to provide enough cortisone to treat one patient for one day, and in 1938 one gram of cortisone cost $100. Today the naturally- occurring diosgenin in Mexican yams can readily be converted into these valuable steroids by simply adding the appropriate chemical group to the already-present steroidal backbone. In fact, more than 60,000 tons of fresh yam tubers are imported into the United States each year for the production of birth control pills. You can also purchase extracts of yams in tablet form that supposedly prevent ovulation and provide a "natural" method of birth control; however, it would be advisable to thoroughly research these claims before trying the latter method on a mate. If in doubt--you might want to try the very effective and foolproof oral contraceptive "Not Now Dear."

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8. Steroids: The Drug Of Champions

Anabolic steroids are essentially the male hormone testosterone and its synthetic derivatives. The latter were developed in the early 1930s to prevent the atrophy of muscle tissue in patients with debilitating illnesses. They were also given to burn victims and surgery patients to speed up tissue rejuvenation. Anabolic steroids entered the athletic scene in Olympic competition in the 1950s, when it was learned that Soviet weightlifters were using them to increase their muscle mass and strength.

And who could ever forget the Seoul Olympics in 1988 when sprinter Ben Johnson of Canada burst out of the starting blocks to win the 100 meter dash, leaving American Carl Lewis in the dust. Three days later the gold medal was given to Lewis because traces of stanozolol (an anabolic steroid) were found in Johnson's urine.

Although athletes have reported remarkable results with steroids, the long-term side effects can be catastrophic--including liver cancer, heart disease, and kidney damage. In addition to tissue building, the steroids can also masculinize one's body. The is particularly noticeable in woman body builders who may grow facial hair as their voice deepens and their breasts decrease in size. Although the FDA has banned most anabolic steroids except for medical use, they are not controlled substances like cocaine and heroin. They are still being smuggled into the United States from Mexico and Europe. Although they started out with Olympians who wanted an edge in their competition, the use of anabolic steroids has now spread to thousands of mediocre athletes who want to look like Mr. Universe.

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A boolean search of "dioscorea + yam" using one of the fine Internet search engines (such as Altavista, Yahoo and Lycos) will lead you to a number of references on yams, including commercial sources for naturopathic extracts from the tuber. In addition to diosgenin, some species also contain a wonder drug called DHEA (dehydroenpiandrosterone), a hormone that is also secreted by adrenal glands in the human body. There is some evidence suggesting that this hormone is anti-carcinogenic, may slow down the aging process, and may control obesity. According to some studies the level of this hormone steadily drops as one ages. Whether this chemical can help us to maintain a healthy, youthful body remains to be seen. There are undoubtedly many other factors affecting the aging process.

In addition to being the world's largest botanical vegetable, true yams belong to one of the largest genera of flowering plants on earth; have probably slowed down the exponential population growth of humans more than any other plant (particularly in highly developed countries); have provided some of the most important drugs to relieve numerous painful and debilitating ailments; contain one of the most promising drugs to combat the aging process; and have provided millions of people with one of the world's most important sources of starch.