Figure 24.11 A. Irregular (bilaterally symmetrical) flowers of a coral tree. B. Parts of a sweet pea flower. C. An inflorescence of a powderpuff "flower" consisting of regular radially symmetrical legume flowers.
Important crop plants include peas, many kinds of beans (e.g., kidney, lima, garbanzo, broad, mung, tepary), soybeans, lentils, peanuts, alfalfa, sweet clover, jicama, licorice, and wattle. Wattle is an Australian tree that is grown commercially as a source of tannins for leather tanning. Carob, another member of this family, is widely used as a chocolate substitute. Several copals (hard resins used in varnishes and lacquers) are obtained from certain legume plants, as are gum arabic and gum tragacanth used in mucilages, pastes, paints, and cloth printing. The hard wood of several tropical leguminous trees (e.g., rosewood) is prized for furniture.
Important dyes, such as indigo, logwood (used in staining tissues for microscope slides and now scarce), and woad-waxen (a yellow dye), come from different legume plants. Locoweeds, belonging to Astragalus—a genus of about 1,600 species—have killed many horses, cattle, and sheep, particularly in the southwestern United States. The poisonous principle in those species affecting livestock seems to vary in concentration according to the soil type in which the plants are growing. Other poisonous legumes include lupines, jequirity beans, black locusts, and mescal beans.
About 90% of the members of the Legume Family exhibit leaf movements, but few are as rapid as those of the sensitive plant (Mimosa pudica), whose leaves fold within seconds in response to a disturbance. Sensitive plants grow as weeds in the tropics and the Deep South of the United States; they are discussed in Chapter 11 and are shown in Figure 11.14. Many of the movements of other legume plant leaves are correlated primarily with day length.
Clovers have been widely used in the past by gatherers of wild food plants. The leaves are difficult to digest in quantity, but the rhizomes were gathered and usually roasted or steamed in salt water, then dipped in grease before being eaten. The seeds of both clovers and vetches also were gathered and either ground for meal or cooked in a little water and eaten as a vegetable. Today, seeds of several legumes, including alfalfa and mung beans, are popular for their sprouts, which are widely used in salads and Oriental dishes. A tropical bean called winged bean (Fig. 24.12) has unusually high levels of protein, and all parts of the plant are edible. It is presently being grown in several widely scattered tropical and subtropical regions and also is being marketed on a limited scale in some temperate zones. It is believed to have great potential for improving the diet of undernourished peoples throughout the tropics.
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