Family Euphorbiaceae

Although many of the members of the Spurge Family are tropical, they are widespread in temperate regions both north and south of the equator. The stamens and pistils are produced

Plants From South The Equator

Figure 24.13 A spurge. A. Inflorescence. B. An individual cyathium.

gland -

male flower-

in separate flowers that often lack a corolla and are inconspicuous. In true spurges (Euphorbia), the female flower is elevated on a stalk called a gynophore and is surrounded by several male flowers that each consist of little more than an anther. Both the female and male flowers are inserted on a cup composed of fused bracts, the cup usually having distinctive glands on the rim. This type of inflorescence is called a cyathium (Fig. 24.13). Sometimes, the inconspicuous flowers are surrounded by brightly colored bracts (e.g., poinsettia, shown in Fig. 7.19) that give the inflorescence the appearance of a single, large flower. Most members of this large family produce a milky latex, and a number of species are poisonous.

Sooner or later, many gardeners experience "urges to purge spurges," as some members of the family (e.g., spotted spurge) are exceptionally aggressive weeds that reproduce very rapidly. Other large tropical spurges closely resemble columnar cacti.

Several economically important plants are cultivated, particularly in frost-free regions. For example, an estimated 90 million metric tons (100 million tons) of cassava are harvested annually from plants cultivated in South America, Africa, and eastern Asia. The roots develop thickened storage areas that resemble large sweet potatoes (shown in Fig. 5.8) and are a diet staple of the tropics, much as white potatoes and cereals are of temperate areas. Poisonous principles are removed by boiling, fermenting, or squeezing out the juice. In dried and powdered form, the cassava is known as farina. In Western countries, tapioca is prepared by forcing heated cassava pellets through a mesh while it is being agitated. Cassava starch is also used as a base for the production of alcohol, acetone, and other industrial chemicals.

Another cultivated spurge of the tropics is the Para rubber tree, the source of the crude rubber from which most rubber products are made today. Although wild South American trees were the original commercial source of rubber, rubber trees have been widely planted in Indonesia, Africa, and adjacent areas. The trees vary in height from less than 5 to

-stigma female flower

- gynophore

Figure 24.13 A spurge. A. Inflorescence. B. An individual cyathium.

over 50 meters (16 to 164 feet) and produce most of the latex in the inner bark. The laticifers in which latex is secreted spiral around inside the trunk at an angle of about 30 degrees. Accordingly, cuts are made at the same angle into the inner bark to obtain maximum yields of latex, which trickles down into collecting cups that are attached to the tree. After collection, the latex is coagulated by chemicals or smoke and then shipped in sheet or crumbled form to processing plants. Sometimes, an anticoagulant is mixed with it, and the liquid is transferred in tankers. Much of the world's rubber goes into the manufacture of automobile and aircraft tires, but other products made from rubber are legion.

The Pará rubber tree should not be confused with a broad-leaved ornamental known as the rubber plant. The rubber plant is popular as a house plant and also produces latex; it is, however, a member of the Fig Family (Moraceae).

The latex of other spurges may hold a key to future sources of fuel and lubricating oils. In 1976, Melvin Calvin, a University of California Nobel Prize winner, proposed the use of latex of gopher plants as a source of materials for oil. He estimated that such plants, which can grow in semidesert areas, would produce 10 to 50 barrels of oil per year on 0.4 hectare (1 acre) of land at a cost of $3 to $10 per barrel.1

A spurge called candelilla occurs in remote areas of Mexico. It produces a wax on its stems that is used in the making of candles and other wax products. Still another spurge produces seeds with a special oil used in plasticizers, and castor oil (from castor beans) is used in the manufacture of nylon, plastics, and soaps. Castor beans themselves are very poisonous—as few as one to three are sufficient to kill a child. The plants grow very rapidly and are popular as ornamentals despite their being one of the leading natural causes of poisoning among American children.

A Mexican jumping bean is the seed of a certain spurge in which a small moth has laid an egg. When the egg hatches, the grub periodically changes position with a jerk, causing the seed to jump. Crown-of-thorns is an ornamental plant with somewhat flexible twisting stems bearing vicious-looking spines. Some believe it to have been the plant from which the crown of thorns for the head of Christ was made. Poinsettias, or Christmas flowers, are favorite yuletide plants in various parts of the world. Tung oil, used in oil paints and varnishes, and Chinese vegetable tallow, a

1. Jojoba, a member of the Box Family (Buxaceae), is a desert shrub with an acorn-sized capsule containing a large oily seed with about 50% liquid wax content. This high-grade wax and another found in the seeds of meadow-foams, which are members of the Meadowfoam Family (Limnanthaceae), are the only known natural substitutes for sperm whale oil, a vital ingredient in engine lubricants. The importing of sperm whale oil into the United States was banned in 1970 to protect the nearly extinct large ocean mammals, and an expensive synthetic substitute is being used. Experiments and research are in progress to find improved strains of jojoba and to test the feasibility of its being grown on a large scale. Two California counties have been using a mixture of petroleum oil and jojoba oil since 1981 in the transmissions of public transportation buses to see if the mixture will keep them from overheating. The results are promising and may reduce the need for transmission oil changes from once every 50,000 miles to once every 100,000 miles.

substance used in the manufacture of soap and candles, are two more commercially important products obtained from the seeds of cultivated members of the Spurge Family.

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