Guayule
Guayule a rubber-producing shrub native to northern Mexico and the southwestern United States. It grows from 2 to 3 feet (60 to 90 cm) high. It has silvery, lance-shaped leaves about 2 inches (5 cm) long and bears tiny white flowers.
The rubber in guayule occurs in tiny globules of latex (a milky juice) within individual cells, chiefly in tissues located just beneath the bark. Unlike the latex found in many other rubber-producing plants, the latex in guayule will not flow from cuts made in the bark. One method of producing guayule rubber is to crush and grind up guayule plants and then to extract the rubber with acetone or some other organic solvent.
Guayule was a major source of natural rubber in the first half of the 20th century. After World War II, however, the production of guayule rubber was discontinued because it was too expensive compared to rubber obtained from rubber trees in Southeast Asia and rubber made from petroleum. Interest in guayule rubber was revived in the mid-1970's as a result of anticipated major shortages of natural rubber and increased costs of petroleum. By the mid-1980's, improved guayule plants and methods of rubber production had been developed, but guayule rubber remained too expensive to produce commercially. In the years following, researchers concentrated on developing useful products from the non-rubber material in the guayule plant.
Guayule is Parthenium argentatum of the composite family, Compositae.