LEGUMES

LEGUMES. Legumes are members of a family of flowering plants known as Leguminosae. It is one of the three largest families of flowering plants, with approximately 690 genera and about 18,000 species. Legumes are a significant component of nearly all terrestrial biomes on all continents except Antarctica. Some are fresh water aquatics, but no truly marine species exist. The species within the family range from dwarf herbs among arctic and alpine vegetation to massive trees in tropical forests.

The leaves usually occur alternately on the stem and are compound, meaning each leaf is divided into separate leaflets. Both pinnate and trifoliate leaves exist. Legumes are easily recognized by the structure of the flower. The flowers are hermaphroditic with male (stamens) and female (pistils) parts in the same flower and usually with five sepals and five petals. The ovary has a single carpel, cavity, and style. The principal unifying feature of the family is the fruit, a pod technically known as a legume. The legume pod is modified in many ways, including flat, winged, thick, thin, straight, coiled, short, long, woody, fleshy, splitting open, or indehiscent to facilitate dispersal by animals, wind, and water.

The family is divided into three subfamilies: Papilionoideae, Caesalpinioideae, and Mimosoideae, identified by their flowers. The Papilionoideae is the largest of the three subfamilies and the most widespread, extending farther into temperate regions. This subfamily can be easily recognized by its butterfly-like flowers. Most of the important legume crop species consumed by humans, including soybean, field pea, chickpea, field bean, and peanut, are in this group.

The subfamily Caesalpinioideae is comprised of tropical or subtropical trees and shrubs. The useful products derived from this subfamily include edible fruits (Tamarindus indica), senna medicine (Senna spp.), hematoxylon red dye from the logwood tree (Haematoxylon campechianum), and resins used in paints, varnishes, inks, plastics, adhesives, and fireworks derived from the copal (Copaifera spp.) tree.

The subfamily Mimosoideae includes species of industrial, forage, browsing, and fodder importance, such as Acacia spp. (Bisby et al., 2000). The Australian black-wood (Acacia melanoxylon) tree provides useful timber, and gum arabic from the tree of that name (Acacia senegal) is used in an array of industrial processes.

Nitrogen Fixation

Most legumes convert atmospheric nitrogen into nitrogenous compounds useful to plants. Root nodules containing Rhizobium bacteria fix free nitrogen for the plants. In return, legumes supply the bacteria with carbon produced by photosynthesis. This symbiosis provides the nitrogen needed by the plants for survival. Root nodules form in all subfamilies except in rare cases among the Caesalpinioideae.

The basic process of nitrogen fixation involves penetration by the Rhizobium through the root hairs into the cortex, where cell division occurs. These tetraploid cells produce the nodules that appear on the root surface. The nodule growth and efficiency are influenced by the carbon-nitrogen ratio of the plant and by the presence in the soil of phosphate, calcium, magnesium, molybdenum, and boron. If the nodules are ineffective, the bacteria may be parasitic on the host plant. Effective nodules contain red leghemoglobin, which can be seen when the nodules are cut. Ineffective nodules are usually small, hard, spherical, and a greenish color inside. Legumes produce more nodules in the tropics in acid soils and soils deficient in phosphorus, calcium, and other nutrients than in temperate areas. Many strains of Rhizobium occur in nature with multiple hosts, and several Rhizobium species occur with one host (Purseglove, 1981). Many scientists suggest inoculating legume seeds with the appropriate strain of Rhizobium for best agricultural results. This inoculation technique is accomplished by mixing the Rhizobium in water to form a slurry and then adding it to the seed.

Origin

The primary temperate legumes used for human food include garden pea (Pisum sativum), field pea (Pisum arvense), winged pea (Tetragonolobus purpureus), green bean (Phaseolus vulgaris), runner bean (Phaseolus coccineus), butter bean (Phaseolus lunatus), lima bean (Phaseolus limensis), soybean (Glycine max), lentil (Lens culinaris), and broad bean (Vicia faba). These legumes originated in humid, subhumid, cool season, subtropical, semiarid, and temperate areas in diverse regions ranging from Southwest Asia and East Asia to the Mediterranean, Peru, Mexico, and Guatemala (Muehlbauer, 1993).

Common tropical legumes consumed by humans include winged bean (Psophocarpus tetragonolobus), jicama (Pachyrhizus erosus and Pachyrhizus tuberosus), chickpea (Cicer arietinum), black-eyed pea (Vigna unguiculata unguiculata), and peanut (Arachis hypogaea). These tropical legumes originated in areas characterized by humid, semiarid, cool season, subtropical, and tropical climates, primarily including South America, Southwest Asia, Ethiopia, India, Japan, China, and West Africa (Hymowitz, 1990).

History. Soybean, one of the most popular legumes, is one of the oldest cultivated crops. Cultivated soybeans probably arose from a wild type in Asia and moved to Europe and North America in the eighteenth century. Soybean soon became the third most important agronomic crop in the United States. Cowpeas were introduced to the West Indies and ultimately spread throughout the southern United States after the seventeenth century. Field beans (Phaseolus spp.) were cultivated by American Indians at the time of the European discovery of North America and soon were introduced to Europe. The popular peanut, introduced into the United States from Brazil when the colonies were established, was commercially developed in the mid-eighteenth century.

Peas, including garden peas, field peas, broad beans, lentils, and chickpeas, were introduced into the Americas from Europe and the Near East. Jicama is grown in Southeast Asia, Mexico, and Central America. Winged beans were introduced into more than sixty countries, primarily subtropical and tropical, after the mid-1970s.

Primary Food Legumes

Soybean (Glycine max). Soybean is the most important legume produced in the agricultural industry worldwide. It is an annual crop, is easy to grow, and is adapted to a temperate climate. A hot weather crop, soybean requires a minimum of 59°F (15°C) for seed germination and mean temperatures of 68–77°F (20°–25°C) for crop growth. Only moderate soil moisture is needed for germination and seedling establishment, but dry weather is essential for dry seed production. Soybeans suffer when the soil is waterlogged, and established plants tolerate drought.

Soybeans should be fertilized with phosphorous, potassium, and micronutrients, and they require typical agricultural field preparation. The important differences among soybean cultivars are day-length response, pest resistance, and production. These varieties are subdivided into groups according to tropical, subtropical, or temperate climate adaptation (Martin, 1988).

Several major obstacles obstruct optimum soybean production. Diseases cause one-eighth of all soybean losses. Noteworthy diseases and their causal agents include bacterial blight (Pseudomonas glycinea), bacterial pustule (Xanthomonas phaseoli var. sojense), and wildfire (Pseudomonas tabaci). However, the most devastating diseases are caused by fungi, including brown stem rot (Cephalosporium gregatum), stem canker (Diaporthe phaseolorum var. batatatis), pod and stem blight (Diaporthe phaseolorum var. sojae), brown spot (Septoria glycines), and sclerotial blight (Sclerotium rolfsii). Mosaic virus disease, root knot nematode (Meloidogyne spp.), and cyst nematode (Heterodera glycines) also cause significant soybean losses.

The chemical composition of mature soybeans varies with the cultivar plus the soil and climate conditions. Generally, the black-seeded cultivars are protein rich with low oil content, and the yellow-seeded types are oil rich with low protein. The nutritional components of dried seeds are 5.0 percent to 9.4 percent water, 29.6 percent to 50.3 percent protein, 13.5 percent to 24.2 percent fat, 14.0 percent to 23.9 percent carbohydrate, 2.8 percent to 6.3 percent fiber, and a large amount of vitamin B. Soybean seeds contain a higher amount of protein than any other pulse and most other foodstuffs.

Soybean oil is about 51 percent linoleic acid, 30 percent oleic acid, and 6.5 percent linolenic acid and is used as a cooking oil, salad oil, shortening, and margarine. Soybean flour is mixed with wheat flour in baked products, such as bread, cakes, cookies, and crackers, and it is also used in ice cream, candy, and pudding. In Asia soybeans are consumed as soybean milk, soy sauce, soups, drinks, breakfast foods, and vegetables. People in eastern Asia eat unripe seeds and dried seeds, and elsewhere these large seeds are consumed as shelled green beans or as dry beans. Both the Bansei and the Green Giant cultivars are among the more popular soybeans. In the West soybeans are a primary ingredient of Worcestershire sauce, made by mixing boiled beans with wheat flour and salt, then fermenting the mixture with the fungus Aspergillus oryzae for up to one week. The fermented beans are submerged in brine and exposed to the sun for several months to extract the flavor. In Indonesia boiled beans are fermented with Aspergillus and formed into cakes.

Soybeans are used industrially in paints, linoleum, inks, soaps, insecticides, and disinfectants. Soy meal, the residue of oil extraction, is a healthy livestock feed (Purseglove, 1981). Soybeans are also used in the pharmaceutical and nutraceutical industries. For example, Ensure glucerna, a dietary aid for diabetics, includes soybeans, and Estroven, marketed as a dietary supplement with natural phytoestrogens, contains isoflavones, a group of antioxidants found in both humans and legumes, extracted from soybeans. While isoflavones do not show antioxidant activity in legumes, they serve various roles as protectants, attractants, and repellents. Because of their antioxidant characteristics, it is possible that isoflavones make a healthy contribution to the human diet.

Groceries and other retail stores sell products that contain soybeans in some form, and American and Oriental restaurants offer foods with soybean constituents. In addition, many products sold as dietary supplements or nutraceuticals in health food stores include soybeans.

Field peas (Pisum arvense and Pisum sativum). The green pea type of field pea became a food source in the sixteenth century. Field peas grow during the cool season and develop flowers and seeds as the days become longer. Field peas have a variety of uses, and production has increased worldwide. At the beginning of the twenty-first century, U.S. production was estimated at 200,000 hectares, and Canadian production exceeded that threefold. Major diseases include Ascochyta blight (Ascochytapisi and Ascochyta pinodella), bacterial blight (Pseudomonas pisi), and fusarium wilt (Fusarium oxysporum f. pisi). Significant insect pests are the pea weevil (Bruchus pisorum), the pea aphid (Illinoia pisi), and particularly the root knot nematode (Meloidogyne incognita). The wrinkled-seed types of field peas are canned in the immature stage, and the smooth-seed types are eaten as dried peas.

Field peas are usually grown as winter annuals in regions receiving 450 to 500 millimeters of rainfall annually. Generally, field peas perform best on well-drained soils with pH between 6.0 and 7.5. Nitrogen fertilization is not needed, but phosphorus, potassium, and sulfur are required (Muehlbauer, 1993).

The nutritional components of dried seeds are 10.6 percent water, 22.5 percent protein, 1 percent fat, 58.5 percent carbohydrate, and 4.4 percent fiber. Fresh green peas are about 74.3 percent water, 6.7 percent protein, 0.4 percent fat, 15.5 percent carbohydrate, and 2.2 percent fiber. These legumes are a major source of human dietary protein worldwide but are of minor importance in the United States. The seeds are consumed as a fresh vegetable and are canned, frozen, and dried. Field pea pods are also edible. Worldwide field pea plants are used for forage, hay, silage, and green manure (Purseglove, 1981).

Field beans (Phaeolus spp. ). Brazil, the United States, Mexico, and Italy are the leading producers of field beans. In the United States the common field bean is grown primarily in New York, Michigan, and west of the Mississippi River. Suitable for a variety of soil types, beans are a warm season annual crop. The optimum temperature is 63–77°F (17–25°C), and the beans need 120 to 130 days without frost.

Field bean crops require fertilization with phosphorus and potassium, and zinc is often needed in residual amounts. Because beans are planted in warm soil after all danger of frost is past, planting dates vary from early April to early July according to geographic location. Dry beans are harvested after the pods turn yellow and prior to seed scattering (Martin and Leonard, 1967). Field beans are subject to a wide array of diseases, including bacterial blight (Xanthomonas phaseoli), anthracnose (Colletotrichum lindemuthianum), and common bean mosaic virus. Insect pests that cause substantial damage and loss are the bean weevil (Acanthoscelides obtectus) and the Mexican bean beetle (Ephilachna varivestris).

Rich in the amino acids lysine and tryptophane, field beans are one of the most important sources of human dietary protein. Dried adzuki beans (Phaseolus angularis), consumed in Japan and China in soups and cakes, are about 21 percent to 23 percent protein, 0.3 percent fat, and 65 percent carbohydrate. Mung beans (Phaseolus aureus) are about 9.7 percent water, 23.6 percent protein, 1.2 percent fat, 58.2 percent carbohydrate, and 3.3 percent fiber. The green mung bean pods are edible, and the fried seeds are popular in India (Purseglove, 1981). Flour from the seeds is used in Indian and Chinese foods, and in the United States grocery chains and restaurants offer mung bean sprouts. Rice beans (Phaseolus calcaratus) are consumed in India, Burma, Malaysia, China, Fiji, and the Philippines. The beans are usually boiled, and the young pods and leaves are also eaten. Rice beans are about 10.5 percent water, 21.7 percent protein, 0.6 percent fat, 58.1 percent carbohydrate, and 5.2 percent fiber.

Central Americans consume the green and dried seeds of the scarlet runner bean (Phaseolus coccineus). Lima or butter beans (Phaseolus lunatus) are eaten fresh, canned, or frozen in the United States. Dried lima beans are 12.6 percent water, 20.7 percent protein, 1.3 percent fat, 57.3 percent carbohydrate, and 4.3 percent fiber. However, the green beans contain about 66.5 percent water, 7.5 percent protein, 0.8 percent fat, 22.0 percent carbohydrate, and 1.5 percent fiber. The mature beans contain the glucoside phaseolutanin, which gives them their characteristic taste. Because the seeds contain hydrocyanic acid, the cooking water should be boiled and changed during preparation to dissipate the acid.

Black grams (Phaseolus mungo) are highly prized in vegetarian diets in India. They can be boiled or eaten whole, and they are ground into a flour used to make porridge or baked into bread and biscuits. The green pods are also edible. Dried black grams are about 9.7 percent water, 23.4 percent protein, 1.0 percent fat, 57.3 percent carbohydrate, and 3.8 percent fiber (Purseglove, 1981).

The most popular and most widely used beans are known as French beans, kidney beans, runner beans, snap beans, and string beans and are sold throughout the world in grocery stores and restaurants. These are the primary protein food in Latin American and tropical Africa, and in Europe and the United States they are grown for the immature pods, which are consumed fresh, canned, and frozen. The popular baked beans are made with any of these types of whole dried beans cooked with tomato sauce.

Winged bean (Psophocarpus tetragonolobus). The winged bean is a perennial vine that climbs by twining. Usually grown as annuals, the plants flower during short days. Scarifying winged bean seeds induces better germination. Seeds are planted anytime during the year and germinate within five to fifteen days. The plants tolerate various soil types, including heavy, poorly drained, riverbank, sandy, and infertile soils. Organic material in soil promotes successful winged bean growth; otherwise a small amount of mineral fertilizer is generally recommended. While few pests attack winged beans, geese and chickens consume the plants, and damage by cowpea aphids and root knot nematodes has been reported (Martin and Delpin, 1978).

Winged bean leaves, flowers, shoots, immature pods, mature dried seeds, and tubers, which are highly nutritious, are primarily consumed in Papua New Guinea, South Asia, and Southwest Asia. The young, tender pods, sliced or chopped, are eaten raw. The mature dried seeds are especially nutritious because of their high protein content, 30 to 42 percent. These mature seeds can be steamed, boiled, fried, roasted, or made into milk or tofu. The beans contain some antinutritional substances, thus the seeds should always be soaked overnight and then boiled in water until tender. Oil derived from winged beans contains behenic acid, linoleic acid, and tocopherols (vitamin E). Behenic acid reduces the digestibility of winged beans. Tocopherols are antioxidants that improve the utilization of vitamin A in the human body.

Winged bean tubers, which have a protein content of 8 to 20 percent, are eaten boiled, steamed, fried, or baked in Burma and Papua New Guinea. Winged bean sprouts and shoots are consumed raw or cooked. Usually only the top three leaves are eaten. The flowers, steamed or fried, taste similar to mushrooms. The seeds contain several antinutritional phytochemicals, such as trypsin and chymotrypsin inhibitors, amylase inhibitors, phytohemagglutinins, and cyanogenic glycosides. The seed inhibitor activity can be safely eliminated only by moist heat, that is, by soaking the seeds for ten hours and then boiling them for thirty minutes. Both vanilla-and chocolate-flavored milks have been produced from the seeds in Thailand. Scientists have developed snacks of the tubers sliced thin, fried, and salted or softened in sugar syrup. Immature winged bean pods are pickled in southern India (Martin and Delpin, 1978). Psophocarpus tetragonolobus lectin is derived from winged bean seeds and is used commercially in medical diagnostics.

Jicama (Pachyrhizus erosus and Pachyrhizus tuberosus). Jicama is a tuberous legume commonly grown in Mexico on commercial farms and intercropped with maize and beans on smaller farms. It is also monocropped in Thailand, Malaysia, and Hawaii. Jicamas are usually grown from seeds, however, sprouted tubers are occasionally used. In Mexico tuber yields are highest when planted in March and harvested from September to November, and in Hawaii maximum tuber yields occur when planted in September or October and harvested five months later. Thus jicamas require a hot subtropical to tropical climate with moderate rainfall. They tolerate some drought but are sensitive to frost. They attract few pests but occasionally are attacked by the rose beetle (Adoretus versutus) and the bean common mosaic virus (Grum, 1990).

The edible portion of jicamas are about 87.1 percent water, 1.2 percent protein, 0.1 percent fat, 10.6 percent carbohydrate, and 0.7 percent fiber. The tubers are eaten raw or cooked. The young pods from Pachyrhizus erosus are prepared like French beans, but the mature seeds and roots of that plant contain a toxic substance known as rotenone. Young pods of Pachyrhizus tuberosus are avoided because they have irritant hairs (Purseglove, 1981).

Chickpea (Cicer arietinum). Chickpea is the major pulse crop in India, where production reaches 7 million hectares. In the United States, chickpeas are primarily grown in California, Washington, and Idaho. These legumes have a high phosphorus requirement, and both potassium and sulfur should be added if the soil is deficient in either. Chickpeas are adapted to dry conditions and generally flourish on well-drained soils of pH 6.0 to 7.5. The major chickpea pests include gram blight (Mycosphaerella rabiei), rust (Uromyces ciceris-arietini), wilt (Rhizoctonia bataticola and Fusarium orthoceras), and gram caterpillar (Heliothis armigera).

Chickpeas are important in India, where the dried seeds are boiled and the green pods and shoots are prepared in a variety of ways. Flour made from chickpeas is used in many Indian confections. The common chickpea, also called garbanzo bean, is used in the United States primarily in salads and as a vegetable side dish. Dried chickpeas are about 9.8 percent water, 17.1 percent protein, 5.3 percent fat, 61.2 percent carbohydrate, and 3.9 percent fiber (Purseglove, 1981).

Peanut (Arachis hypogaea). Peanuts, called groundnuts in other parts of the world, are one of the most important crops in the southern United States, primarily in Georgia, Texas, Oklahoma, North Carolina, Alabama, and Virginia. Other leading production countries include India, China, Nigeria, Senegal, Indonesia, and Brazil. An annual crop with a growing season from 1 May to 1 November in the United States, the peanut prefers sandy loam soils. Adequate soil moisture and high temperatures are necessities for seed germination and plant growth. Peanuts respond best when the pH is above 5. The American peanut is classified into three botanical types based on the shape of the nut and growth characteristics: Virginia (bunch and runner growth types), Spanish (bunch growth type), and Valencia (bunch growth type). Crop rotation is recommended because peanut yields are good following cotton or other nonleguminous crops, and applications of lime and potash usually increase yields. Peanuts suffer from cercospora leaf spots (Cercospora arachidicola and Cercospora personata), stem and peg rots (Sclerotium rolfsii), and tomato spotted wilt virus.

Peanuts are consumed by humans throughout the world as peanut butter, in candies, and as cooking oil. Peanut oil is about 53 percent oleic acid and 25 percent linoleic acid. The Virginia peanut is 38 percent to 47 percent oil, and the Spanish peanut is 47 percent to 50 percent oil. Shelled peanuts are about 5.4 percent water, 30.4 percent protein, 47.7 percent fat, 11.7 percent carbohydrate, and 2.5 percent fiber. The primary proteins in peanuts are arachin and conarachin, and peanuts are rich in vitamins B and E (Pattee and Young, 1982). Some people have allergenic reactions to certain types of peanuts. The peanut allergens designated as Ara h 1, Ara h 2, and Ara h 3 are glycoproteins with a molecular mass of 63 kilodaltons and are present in raw and roasted peanuts since they are heat stable and may be found in any peanut type. Peanut proteins, including arachin, conarachin, peanut agglutinin, and peanut phospholipase, can also be allergens. Other important phytochemicals in peanuts are protocatechuic acid, which has shown potential antioxidant and pesticidal qualities, and lecithin, which has shown antioxidant activity (Beckstrom-Sternberg and Duke, 1994). A lectin derived from peanuts is used commercially in medical diagnostics.

Cowpea (Vigna spp. ). Cowpeas led U.S. legume production until about 1941, when they were replaced by soybeans, clovers, and other special-purpose legumes. Cowpeas are produced in California on a fairly large scale, and they are cultivated in Africa, southern Asia, and the Mediterranean region of Europe. A short-day, warm-weather crop, they should be planted in warm soil after all danger of frost has passed. However, severe drought will prevent seed formation. Cowpeas grow well in sandy or clay soils with good water drainage. The common black-eyed pea (Vigna unguiculata) is by far the most important cowpea variety.

Common diseases include cowpea wilt (Fusarium oxysporum var. tracheiphilum), cowpea root knot nematode (Meloidogyne spp.), charcoal rot (Macrophomina phaseoli), and viral diseases. The chief insect problems are the cowpea weevil (Callosobruchus maculatus) and the southern cowpea weevil or four-spotted bean weevil (Mylabris quadrimaculatus).

Legumes Cultivated for Phytochemicals

Jack beans (Canavalia ensiformis) are cultivated primarily for their phytochemicals. The ripe, dried seeds are about 11.0 percent water, 23.4 percent protein, 1.2 percent fat, 55.3 percent carbohydrate, and 4.9 percent fiber (Purseglove, 1981). Jack bean seeds are the only source of the lectin known as concanavaline-A, which is used in medical diagnostics. Lectins extracted from several other legumes, including sunn hemp (Crotalaria juncea), red kidney beans (Phaseolus vulgaris), and field peas (Pisum sativum), are used in medical diagnostics also. Guar seeds (Cyamopsis tetragonolobus) contain galactomannan gum, which is used in food additives; industrials; pharmaceuticals; confectionaries, including cereal, ice cream, and candy (Whistler and Hymowitz, 1979); and nutraceuticals, such as Ensure glucerna.

Kudzu (Pueraria spp.) produces isoflavones used in nutraceuticals for natural estrogen therapy, such as Estroven. A nutraceutical known as kudzu root is sold in powder form. Velvet bean (Mucuna pruriens) extract is

marketed as an antiparkinsonian herbal supplement or nutraceutical. See Table 1 for additional legume phytochemicals.

Legumes Cultivated for Animal Food

Legume species used for forage include Aeschynomene, Desmodium, Leucaena, Macroptilium, Neonotonia, Stylosanthes, Desmanthus, Macrotyloma, Sesbania, and Trifolium. Several species, including Desmanthus virgatus, Stylosanthes scabra, and Stylosanthes guianensis, have been tested in the southeastern United States for possible forage production. Stylosanthes hamata, Stylosanthes humilis, Macroptilium atropurpureum, Macroptilium bracteatum, Neonotonia wightii, and Lotononis bainesii are grown successfully as pasture legumes in Australia and show potential for use in the United States (Morris, 1997).

Other Uses for Legumes

Several legumes have multiple uses as human foods, animal feeds, ornamentals, cover crops, green manure, and erosion control plants. Minor legumes used primarily for cover crops, forage, and green manure worldwide include calopo (Calopogonium mucunoides), centro (Centrosema pubescens), and tropical kudzu (Pueraria phaseoloides) (Morris, 1997).

Indigofera arrecta was once cultivated in India for indigo dye, but it declined significantly with synthetic dye production. In Central Africa, however, indigo dye derived from the plant is still used. Dhaincha (Sesbania bispinosa) produces galactomannan gum and is grown also for soil improvement, fiber for paper pulp, fodder, and its ornamental qualities. Lead trees (Leucaena leucocephala), similar in growth to mimosa trees, are used for paper products and as cover crops, fodder, pastures, green manure, and ornamentals (Morris, 1997). Other legumes are important in reclamation of mined soils, polluted soils, deforested areas, and soils with poor nutritional conditions (Morris, 1997).

Legume Traditions

The expression "blackball" comes from the ancient Greek and Roman practice of using beans for voting. A white bean signifies acceptance, while a black bean means rejection. The black-eyed pea is eaten on New Year's Day in the southern United States to bring good luck for the coming year.

The Navaho-Ramah Indian tribe used an annual clover known as Trifolium dubium as a ceremonial medicine. For a dermatological remedy the Iroquois used a wild bean known as Strophostyles helvola, and the Pawnees used spider bean (Desmodium illinoensis). Bush clover or rabbit foot (Lespedeza capitata) was an antidote in the Fox tribe and an analgesic for the Omahas and Poncas. The Cherokees chewed tickseed or trefoil (Desmodium

perplexum) roots for sore gums and mouths. The Mohegans made a blood purifier from rattle box (Crotalaria sagittalis) root, and the Delawares treated venereal disease with rattle box root (Beckstrom-Sternberg, Duke, and Wain, 1994). See Table 2 for additional ethnobotanical and multicultural uses of legumes.

See also Nuts; Peanut Butter; Peas.

BIBLIOGRAPHY

Beckstrom-Sternberg, Stephen M., and James A. Duke. "The Phytochemical Database." Data version July 1994. Available at http://ars-genome.cornell.edu/cgi-bin/WebAce/webace?db=phytochemdb.

Beckstrom-Sternberg, Stephen M., James A. Duke, and K. K. Wain. "The Ethnobotany Database." Data version July 1994. Available at http://ars-genome.cornell.edu/cgi-bin/WebAce/webace?db=ethnobotdb.

Bisby, Frank A., James L. Zarucchi, B. D. Schrire, Y. R. Roskov, and Richard J. White, eds. International Legume Database and Information Service. 5th ed. Reading, U.K.: ILDIS, 2000.

"Ecology." In The Columbia Encyclopedia, edited by Paul Lagassé. 6th ed. New York: Columbia University Press, 2000.

Grum, Mikkel. Breeding Pachyrhizus Rich. Ex DC.: A Review of Goals and Methods. Copenhagen, Denmark: Royal Veterinary and Agricultural University, Department of Crop Husbandry and Plant Breeding, 1990.

Hymowitz, Theodore. "Grain Legumes." In Advances in New Crops, edited by Jules Janick and James E. Simon. Portland, Oreg.: Timber Press, 1990.

Martin, Franklin W. Soybean. Fort Myers, Fla.: Educational Concerns for Hunger Organization, ECHO Technical Note, 1988.

Martin, Franklin W., and Herminio Delpin. Vegetables for the Hot, Humid Tropics. Part 1: The Winged Bean, "Psophocarpus Tetragonolobus." New Orleans: Department of Agriculture, Science, and Education Administration, 1978.

Martin, John H., and Warren H. Leonard. "Legumes." In Principles of Field Crop Production. 2d ed. New York: Macmillan, 1967.

Morris, John Bradley. "Special-Purpose Legume Genetic Resources Conserved for Agricultural, Industrial, and Pharmaceutical Use." Economic Botany 51, no. 3 (July–September 1997): 251–263.

Muehlbauer, Fred J. "Food and Grain Legumes." In New Crops, edited by Jules Janick and James E. Simon. New York: Wiley, 1993.

Pattee, Harold E., and Clyde T. Young, eds. Peanut Science and Technology. Yoakum, Tex.: American Peanut Research and Education Society, 1982.

Purseglove, J. W. "Leguminosae." In Tropical Crops: Dicotyledons. 2 vols. New York: Wiley, 1987.

Whistler, Roy L., and Theodore Hymowitz. Guar: Agronomy, Production, Industrial Use, and Nutrition. West Lafayette, Ind.: Purdue University Press, 1979.

Brad Morris

Glossary

Biome —The world's major communities classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment

Carpel —A single member of a compound seed-bearing flower organ.

Cortex —The primary plant tissue between the vascular system and the epidermis of the stem and the root.

Cover crop —A crop grown between orchard trees or on fields between cropping seasons to protect the land from leaching of nutrients and erosion.

Diversity —Variety of life on the planet.

Fodder —Coarse plants harvested whole and cured in an erect position.

Forage —Plant matter, fresh or preserved, gathered and fed to animals.

Green manure —Any crop or plant grown and incorporated into the soil.

Hay —Fine-stemmed plants cut and cured for forage.

Heme —Iron-protoporphyrin IX, a ubiquitous prosthetic group structurally associated to many enzymatic, regulatory, transport, and binding proteins.

Herbivorous— Animals that consume only plant material.

Indehiscent —Remaining persistently closed.

Lectin —Proteins or glycoproteins of nonimmune origin that agglutinate cells and precipitate complex carbohydrates. They are valuable for blood grouping and erythrocyte polyagglutination, mitogenic stimulation of lymphocytes, lymphocyte subpopulation studies, fractionation of cells and other particles, and histochemical studies of normal and pathological conditions.

Leghemoglobin —Heme-containing, oxygen-binding protein found in plants.

Ovary —The part of the pistil (the seed-bearing flower organ) that contains the ovules.

Parasitic —An organism living or feeding on another organism to the detriment of the host organism.

Pasture —Land with forage plants used for grazing animals.

Petal —A division of the corolla (the inner floral envelope).

Pinnate leaf —Compound leaf with leaflets arranged on each side of a common axis.

Pulse —Legume plants or seeds used for food.

Sepal —A division of a calyx (the outer floral envelope).

Silage —Forage preserved in a succulent condition by partial fermentation in a tight container.

Style —The portion of the seed-bearing flower organ that connects the stigma and the ovary.

Tetraploid —An organism whose cells contain four haploid (4n) sets of chromosomes or genomes.

Trifoliate —Having three leaflets.

Uses for Legumes

Senna occidentalis —Potential bactericidal, pesticidal, and viricidal plant. It also contains tannin, which is an antidiarrhetic, an antioxidant, and an antiviral agent and has cancer preventive potential.

Crotalaria juncea —Sunn hemp, known as a multiple-use small-tree crop. It is used in paper making and as green manure and has bactericidal qualities. Sunn hemp contains pectin, which has antidiabetic, antidiarrhetic, antitumor, antiulcer, and cancer preventive potential. Sunn hemp has been used in Iraq to treat psoriasis.

Mucuna pruriens —Velvet bean, a green manure crop and a nutraceutical in the United States. The seeds contain L-dopa, which is used in the treatment of Parkinson's disease, beta-sitosterol, a potential anti-inflammatory, antileukemic, antitumor, cancer preventive, and estrogenic agent; gallic acid, a potential antioxidant, antiseptic, antiviral agent, and cancer preventive; and lecithin, a potential Alzheimer's preventive. Velvet bean is also used in India, Venezuela, and Mexico to treat asthma, snake bites, cancer, coughs, diarrhea, mumps, ringworm, syphilis, and tumors and as a scorpion antidote.

Legumes

Biology of legumes

Native legumes of North America

Legumes in agriculture

Legumes in horticulture

Legumes as weeds

Resources

Legumes or beans are species of plants in the family Fabaceae (also known as Leguminoseae), a very large family containing about 12,000 species and 440 genera with species occurring on all of the habitable continents.

The most species-rich groups in the legume family are the milk vetches (Astragalus spp.) with 2,000 species, indigos (Indigoifera spp.; 500 species), clovers (Trifolium spp.; 300 species), beans (Phaseolus spp.; 200 species), and lupines (Lupinus spp.; 200 species). Although some taxonomists include the closely related species of the families Caesalpinaceae (about 2,200-3,000 species) and Mimosaceae (3,000 species) with the legume family, the greater legume family includes the Fabaceae, Caesalpinaceae, and Mimosaceae.

Some legume species are very important as food plants for humans and livestock. Economically legumes are second in agricultural importance only to the cultivated species of the grass family, such as wheat, maize, and rice. Because many legume species can utilize nitrogen gas (N₂) in the atmosphere, their foliage and fruits are relatively rich in proteins and are important sources of nutrients for humans and animals. Some legumes are also used as ornamental plants.

Biology of legumes

Legume species represent a wide variety of growth forms, ranging from annual plants to herbaceous perennials to woody shrubs, vines, and trees.

The leaves of legumes are typically arranged alternately on the stems and are commonly compound, meaning that each leaf is composed of several to many leaflets arranged along a central stalk. In some herbaceous climbing species, leaflets are modified into spirally winding clinging organs known as tendrils.

Legume flowers are bilaterally symmetrical and generally arranged into groups known as inflorescences. The five petals are modified into distinctive structures. The topmost petal is called the banner or standard, the two lateral petals are called wings, and the bottom two are fused into a structure known as the keel, which encloses the ten stamens and single pistil of the flower. Legume flowers are usually scented, brightly colored, and contain nectar. All of these are adaptations to attract flying insects who are pollinate the flowers.

Legume fruits are dry or fleshy multiseeded structures known as legumes or pods. The fruits and seeds

of some species are highly nutritious because of their large concentrations of protein. The seeds of some species, however, contain toxic alkaloids and can be poisonous.

About half of all legume species have bumpy nodules on their roots that house symbiotic (or mutualistic) bacteria with the ability to “fix” atmospheric nitrogen gas into ammonia, which the plant then uses as a nutrient to synthesize proteins. The bacteria responsible for nitrogen fixation in legumes are in the genus Rhizobium with separate strains or species associated with each symbiotic legume species. The Rhizobium bacteria have the ability to synthesize a chemical known as nitrogenase, an enzyme that can cleave the very strong triple bond of nitrogen gas (N₂)

(NH₃) to produce ammonia. Because nitrogen gas is otherwise inert to biological reactions, while ammonia (as ammonium ion, NH₄⁺) is a chemical that plants can easily utilize for nutrition, nitrogen fixation is an extremely useful function. Legumes that have symbiotic Rhizobium living in their root nodules may have important ecological advantages in competition with other types of plants, especially if they are growing in otherwise nitrogen-poor habitats.

Native legumes of North America

Many species in the legume family are indigenous to the natural plant communities of North America. Numerous other species have been introduced from Eurasia, Africa, and elsewhere, and are now naturalized in North America. The introduced plants are mostly species that are grown in agriculture or horticulture and were able to escape from cultivation to establish wild populations.

Native legume species of are among the most beautiful and engaging wildflowers of North America. Some of the most interesting and attractive include the wild lupines (such as Lupinus perennis ), false blue indigo (Baptisia australis), wild indigo (B. tinctoria), tick-trefoils (Desmodium spp.), bush-clovers (Lespedeza spp.), beach pea (Lathyrus maritimus) and marsh pea (L. palustris), milk-vetches, and loco-weeds (Oxytropis spp.).

Some North American examples of tree-sized legumes that occur in temperate climates include the black locust (Robinia pseudoacacia), yellow-wood (Cladrastis lutea), redbud (Cercis canadensis), honey locust (Gleditsia triacanthos), and Kentucky coffee tree (Gymnocladus dioica). These are all native to the eastern United States, but are cultivated as ornamentals more widely, sometimes escaping into roadside and secondary-forest habitats.

Other native species occur in subtropical habitats in the southern United States. These include the eastern coralbean (Erythrina herbacea) of the southeastern states, Bahama lysiloma (Lysiloma bahamensis), and fish-poison tree (Piscidia piscipula) of southern Florida. Subtropical legumes in the southwestern states include cattail acacia (Acacia greggii), sweet acacia (A. farnesiana), and other acacias, along with species of leadtrees (Leucaena spp.) and blackbeads (Pithecellobium spp.).

Legumes in agriculture

Some species of legumes are important foods for humans and domestic livestock. Their seeds are typically highly nutritious and rich in protein, carbohydrates, oils, fiber, and other nutrients. However, the protein-rich nature of legume seeds, a consequence of their nitrogen-fixing symbiosis, is perhaps their most important attribute as a food. Numerous species of legumes are grown in agriculture, and it is likely that there are other species of legumes of potential agricultural importance that have not yet been discovered, especially in the tropics.

One of the most important agricultural legumes is the peanut or groundnut (Arachis hypogaea), originally native to Brazil but now cultivated much more widely. After the aboveground flowers of the peanut are pollinated, the supporting stem turns and forces its way into the ground where the flowers then develop into their familiar, shelled fruits. Peanuts can be eaten raw or roasted, pulverized into peanut butter, or as an ingredient in cakes and cookies. Peanuts are also used to manufacture an edible oil. Sometimes a fungus known as Aspergillus flavus will infest stored peanuts. This fungus will excrete a potent toxic known as aflatoxin, which can cause liver damage and possibly lead to the development of cancers. In addition, some people develop an extreme allergy to peanuts, and these hypersensitive individuals can be killed by inadvertently eating any food containing peanuts.

Another very important species of legume is the soybean (Glycine max), originally native to Southeast Asia. This species can be eaten cooked or as fresh sprouts, or it can be processed into a protein-rich material known as tofu, another substance known as soy flour, or into a nutritious drink known as soy-milk. Soybeans are important ingredients in some of the meat substitutes that have recently been developed such as vegetarian hot dogs. Soybeans are also pressed to produce edible oils.

The seeds of many other legume species are also eaten. These include the chick-pea (Cicer arietinum), lentil (Lens esculenta), common pea (Pisum sativum), broad or faba bean (Vicia faba), cowpea (Vigna sinensis), common bean (P. vulgaris), mung bean (Phaseolus aureus), lima bean (P. lunatus), and scarlet runner bean (P. multiflorus). The entire pod of the carob (Ceratonia siliqua) can be eaten and is similar to a candy because of the naturally large concentration of sugar that it contains.

The licorice (Glycyrrhiza glabra) is a perennial herb that is native to southern Europe and Asia and is now cultivated more widely. The rhizome of licorice is used mostly in the preparation of candy and to much smaller degrees to prepare medicinals, shoe polish, and to flavor tobacco.

Some legume species are important in agriculture as nitrogen-rich forages for domestic livestock. Those commonly cultivated in North America include alfalfa or lucerne (Medicago sativa), sweet clovers (Melilotus officinalis and M. alba), bird’s-foot trefoil (Lotus corniculatus), vetches (Vicia cracca and other species), and various species of clovers, including red clover (Trifolium pratense), white clover (T. repens), hop clovers (T. agrarium and T. procumbens ), and alsike clover (T. hybridum). Legumes are also used as a “green manure” or soil conditioner that is grown and then plowed into the ground to organic matter and fixed nitrogen in the soil.

Other economic products obtained from legumes

Many tree-sized legume species are valuable for their hard, durable timber. North American species are relatively minor in this respect, although the Kentucky coffee tree, black locust, and honey locust are used as lumber to some degree.

Some leguminous species of tropical hardwoods are highly prized for fine woodworking. Purpleheart (Peltogyne paniculata) is a very hard, strong, and durable wood found in northern South America; a brownish color when first sawed, it turns a spectacular purple after exposure to the atmosphere. This tropical hardwood is used to manufacture fine furniture and as a decorative inlay into other woods. Rosewoods also have hard, dark-purple woods that are widely sought after to manufacture fine furniture and other goods. Examples include Brazilian (Dalbergia nigra) and Asian rosewoods (D. latifolia and D. sissoo ).

Various Acacia tree species are also important sources of lumber, for example, A. melanoxylan and A. visco in Australia. Species of Albizia are also important timber trees.

Mesquite seeds (Prosopis juliflora), found in the southwestern United States and Mexico, are used as animal feed, and while the wood is burned to manufacture a flavor-enhancing charcoal. Mesquite flavorings are popular, and many foods are now seasoned with this plant, including potato and corn chips.

Sunn is a fiber obtained from Crotalaria juncea, a legume native to south Asia. This is an annual plant, grown mostly in the Indian subcontinent and used to manufacture twine, ropes, bags, and canvas.

Gums are plant compounds used as adhesives, to manufacture paints and candies, prepare paper, and manufacture certain medicines. Important gums are made from extracts of certain legume species including gum tragacanth from Astragalus gummifer, gum arabic from Acacia senegal and A. stenocarpa, and tragasol from the carob (Ceratonia siliqua).

The barks of some acacia species are sometimes used as sources of tannins, chemicals that are used mostly to manufacture leather from animal skins. Species used for this purpose include Acacia dealbata, A. decurrens, and A pycnantha, all native to Australia but also cultivated elsewhere.

Some important dyes are extracted from species in the legume family. One of the world’s most important natural dyes is indigo, extracted from the indigo (Indigofera tinctoria) plant of south Asia and to a lesser degree from American indigo (I. suffruticosa) of tropical South America. Indigos are still cultivated widely for their dark-blue dye, although similar chemicals have been synthesized since 1900 and are widely available.

Other important natural dyes are obtained from the heartwood of several species of leguminous trees. Logwood (Haematoxylon campechianum) is a small, thorny tree native to Central America that is an important source of a dye known as hematoxylin, which has a deep, purple-red color, and can also be manufactured into a persistent black dye. The brazilette (H. brasiletto) is a source of a natural red dye as are brazilwood (Caesalpina brasiliensis) and sappanwood (C. sappan) of south Asia.

Derris or rotenone is a poisonous alkaloid that has long been used by indigenous peoples of Southeast Asia for arrow and fish poisons. Rotenone is now used widely as a rodenticide and insecticide. This chemical is mostly extracted from the plants Derris elliptica and D. malaccensis.

Shellac is now a relatively minor product, but until recently it was widely used for finishing wood and for manufacturing products such as phonograph records and electrical insulators. Shellac is derived from a sticky substance that is secreted by an Asian insect, Tachardia lacca. However, several species in the legume family are cultivated as hosts for the insect, including the pigeon pea (Cajanus cajan) and babul tree (Acacia arabica).

Legumes in horticulture

Some legumes are important in horticulture, where they are typically grown for their beautiful flowers and sometimes as foliage plants. The scotch broom (Cytisus scoparius) is a green-stemmed bushy shrub with attractive yellow flowers. Gorse (Ulex europaeus) is also a shrub with spiny branches and bright yellow flowers. These are widely used in horticulture in temperate climates, as are the North American trees, redbud, Kentucky coffee tree, and black and honey locust. Some nonnative horticulture species found in temperate North American climates include species of laburnum such as Scotch laburnum (Laburnum alpinum) and common laburnum (L. anagyroides).

Many other leguminous trees and shrubs are grown as ornamentals in subtropical and tropical climates. Species cultivated in southern parts of the United States include the royal poinciana (Delonix regia) of Madagascar, the paradise poinciana (D. gilliesii) of South America, the tamarind (Tamarindus indica) of south Asia, and the silk tree (Albizia julibrissin) and woman’s tongue (A. lebbek) of south Asia.

Various species of garden lupines (Lupinus) are grown for their tall attractive spikes of colorful flowers. Commonly grown species include L. polyphyllus and L. nootkatensis whose flowers are naturally blue but also occur in white, pink, red, and other floral cultivars.

Other legumes that are commonly grown in gardens include the Japanese wisteria (Wisteria floribunda),

KEY TERMS

Bilateral symmetry —In reference to flower shape, this indicates that a vertical sectioning of the flower will produce two halves with symmetric features.

Compound leaf —A leaf in which the blade is separated into several or many smaller units, called leaflets, arranged along a central petiole or stalk known as a rachis.

Cultivar —A distinct variety of a plant that has been bred for particular, agricultural or culinary attributes. Cultivars are not sufficiently distinct in the genetic sense to be considered to be subspecies.

Legume —This is a type of fruit, also known as a pod, which is developed from a single ovary but contains multiple seeds and opens along a single seam when ripe.

Nitrogen fixation —The conversion of atmospheric nitrogen gas (N₂) to ammonia or an oxide of nitrogen.

This process can occur biologically through action of the microbial enzyme, nitrogenase, or inorganically at high temperature and pressure.

Nitrogenase —An enzyme synthesized by Rhizobium and some other microorganisms that is capable of cleaving the triple bond of nitrogen gas (N₂), generating ammonia (NH₃), a type of fixed nitrogen that plants can utilize in their nutrition.

Rhizome —This is a modified stem that grows horizontally in the soil and from which roots and upward-growing shoots develop at the stem nodes.

Tendril —A spirally winding, clinging organ that is used by climbing plants to attach to their supporting substrate. In the legume family, tendrils are derived from modified leaflets.

Weed —Any plant that is growing abundantly in a place where humans do not want it to be.

Chinese wisteria (W. sinensis), and related species. The sweet pea (Lathyrus odoratus) is also commonly grown as an attractive, climbing plant.

Legumes as weeds

Some species of legumes that are cultivated in agriculture or horticulture have become naturalized in seminatural and natural habitats, and some of these are considered invasive weeds. Examples of these species include Scotch broom, gorse, garden lupines, vetches, and some other species. These are rarely considered important enough as weeds to be the specific targets of control programs.

One exception, however, is the kudzu vine (Pueraria lobata), native to Japan and introduced to the southeastern United States as a forage plant and to control erosion. This species has become a serious, invasive weed in some places. Control methods include the use of herbicides and the excavation of its large, underground, roots.

A few species of legumes have foliage or seeds that can be extremely toxic to humans and domestic animals, and these may be actively controlled to reduce the risks of poisoning. The best North American examples of toxic legumes that are sometimes considered to be pests because they can poison livestock on rangelands are the locoweeds (Oxytropis spp., and to a lesser degree, Astragalus spp.). The precatory pea or rosary bean (Abrus precatorius) that now grows wild in subtropical and tropical climates was introduced as an ornamental plant to south Florida where it is now naturalized. This species has small (less than 0.4-inch [1 cm] long) very attractive crimson seeds with a jet-black spot at one end, but these are so toxic that a single one can kill a person if chewed. Precatory peas are sometimes used to make beautiful seed-necklaces, but these can be deadly in the hands of children.

Resources

BOOKS

Duke, J. A. Handbook of Legumes of World Economic

Importance. New York: Plenum Press, 1981.

Judd, Walter S., Christopher Campbell, Elizabeth A.

Kellogg, Michael J. Donoghue, and Peter Stevens. Plant Systematics: A Phylogenetic Approach. 2nd ed. with CD-ROM. Suderland, MD: Sinauer, 2002.

Klein, R.M. The Green World: An Introduction to Plants and

People. New York: Harper and Row, 1987.

OTHER

Food and Agriculture Organization of the United Nations.

“Forage Tree Legumes in Tropical Agriculture” <http://www.fao.org/ag/AGP/AGPC/doc/Publicat/Gutt-shel/x5556e00.htm> (accessed December 2, 2006).

Purdue University, Horticulture and Landscape Architecture. “Grain Legumes” <http://www.hort.purdue.edu/newcrop/proceedings1990/V1-154.html> (accessed December 2, 2006).

Bill Freedman

Legumes

Legumes or beans are species of plants in the family Fabaceae (also known as Leguminoseae). The legume family is very large, containing about 12,000 species and 440 genera with species occurring on all of the habitable continents.

The most species-rich groups in the legume family are the milk-vetches (Astragalus spp.) with 2,000 species, indigos (Indigoifera spp.; 500 species), clovers (Trifolium spp.; 300 species), beans (Phaseolus spp.; 200 species), and lupines (Lupinus spp.; 200 species). Although some taxonomists include the closely related species of the families Caesalpinaceae (about 2,200-3,000 species) and Mimosaceae (3,000 species) with the legume family, the greater legume family includes the Fabaceae, Caesalpinaceae, and Mimosaceae.

Some species of legumes are very important as food plants for humans and livestock . Economically legumes are second in agricultural importance only to the cultivated species of the grass family, such as wheat , maize, and rice . Because of the ability of many legume species to utilize nitrogen gas (N2) in the atmosphere, the foliage and fruits of many legumes are relatively rich in proteins and are important sources of nutrients for humans and other animals. Some species of legumes are also used as ornamental plants in horticulture .

Biology of legumes

Legume species represent a wide variety of growth forms, ranging from annual plants to herbaceous perennials to woody shrubs, vines, and trees.

The leaves of legumes are typically arranged alternately on the stems and are commonly compound, meaning that each leaf is composed of several to many leaflets arranged along a central stalk. In some herbaceous, climbing species of legumes, some of the leaflets are modified into spirally winding, clinging organs known as tendrils.

The flowers of legumes are bilaterally symmetric and are generally arranged into groups known as inflorescences. The five petals are modified into distinctive structures. The top-most petal is called the banner or standard, the two lateral petals are called wings, and the bottom two are fused into a structure known as the keel, which encloses the ten stamens and single pistil of the flower . Legume flowers are usually brightly colored, and they contain nectar and are often scented. All of these are adaptations for attracting flying insects who are the pollinators of the flowers of legumes.

The fruits of legumes are dry or fleshy, multi-seeded structures known as legumes or pods. The fruits and seeds of some legume species are highly nutritious because of their large concentrations of protein. The seeds of some species, however, contain toxic alkaloids and can be poisonous.

About one-half of the species of legumes have bumpy nodules present on their roots which house symbiotic (or mutualistic) bacteria that have the ability to metabolically fix atmospheric nitrogen gas into ammonia which can be utilized by the plant as a nutrient for the synthesis of proteins. The bacteria responsible for nitrogen fixation in legumes are in the genus Rhizobium with separate strains or species associated with each species of symbiotic legume. The Rhizobium bacteria have the ability to synthesize a chemical known as nitrogenase which is an enzyme that can cleave the very strong triple bond of nitrogen gas (N2) so that ammonia (NH3) is produced. Because nitrogen gas is otherwise inert to biological reactions, while ammonia (as ammonium ion, NH + 4 ) is a chemical that plants can easily utilize in their nutrition , nitrogen fixation is an extremely useful function. Legumes that have symbiotic Rhizobium living in their root nodules may have important ecological advantages in competition with other types of plants, especially if they are growing in otherwise nitrogen-poor habitats.

Native legumes of North America

Many species in the legume family are indigenous to the natural plant communities of North America . Numerous other species of legumes have been introduced by humans from Eurasia, Africa , and elsewhere and are now naturalized in suitable habitats in North America. The introduced plants are mostly species that are grown in agriculture or horticulture and were able to escape from cultivation and establish wild populations.

Native species of legumes are among the most beautiful and engaging wildflowers of North America. Some of the most interesting and attractive groups of native legumes include the wild lupines (such as Lupinus perennis), false blue indigo (Baptisia australis), wild indigo (B. tinctoria), tick-trefoils (Desmodium spp.), bush-clovers (Lespedeza spp.), beach pea (Lathyrusmaritimus) and marsh pea (L. palustris), milk-vetches, and loco-weeds (Oxytropis spp.).

Some North American examples of tree-sized legumes that occur in temperate climates include the black locust (Robinia pseudoacacia), yellow-wood (Cladrastis lutea), redbud (Cercis canadensis), honey locust (Gleditsia triacanthos), and Kentucky coffee tree (Gymnocladus dioica). These are all native to parts of the eastern United States but are cultivated as ornamentals more widely, sometimes escaping into roadside and secondary-forest habitats.

Other native species of legumes occur in subtropical habitats in the southern United States. These include the eastern coralbean (Erythrina herbacea) of the southeastern states, Bahama lysiloma (Lysiloma bahamensis), and fish-poison tree (Piscidia piscipula) of southern Florida. Subtropical legumes in the southwestern states include cattail acacia (Acacia greggii), sweet acacia (A. farnesiana), and other acacias, along with species of leadtrees (Leucaena spp.) and blackbeads (Pithecellobium spp.).

Legumes in agriculture

Some species of legumes are very important as foods for humans and domestic livestock. The seeds of legumes are typically highly nutritious and rich in protein, carbohydrates, oils, fiber, and other nutrients. However, the protein-rich nature of legume seeds, a consequence of their nitrogen-fixing symbiosis , is perhaps their most important attribute as a food for animals. Numerous species of legumes are grown in agriculture, and it is likely that there are other species of legumes of potential agricultural importance that have not yet been discovered, especially in the tropics.

One of the most important agricultural legumes is the peanut or ground-nut (Arachis hypogaea), originally native to Brazil but now cultivated much more widely. After the above-ground flowers of the peanut are pollinated, their supporting stem turns and forces its way into the ground where the flowers then develop into their familiar, shelled fruits. Peanuts can be eaten raw or roasted, pulverized into peanut butter, or baked into cakes and cookies. Peanuts are also used to manufacture an edible oil. Sometimes a fungus known as Aspergillus flavus will infest stored peanuts. This fungus will excrete a potent toxic known as aflatoxin which can cause liver damage and perhaps lead to the development of cancers. In addition, some people develop an extreme allergy to peanuts, and these hypersensitive individuals can be killed by inadvertently eating any food containing peanuts.

Another very important species of legume is the soybean (Glycine max), originally native to Southeast Asia . This species can be eaten cooked or as fresh

sprouts, or it can be processed into a protein-rich material known as tofu, another substance known as soy flour, or into a nutritious drink known as soy-milk. Soybeans are important ingredients in some of the meat substitutes that have recently been developed such as vegetarian hot dogs. Soybeans are also pressed to produce edible oils.

The seeds of many other species of legumes are also eaten. These include the chick pea (Cicer arietinum), lentil (Lens esculenta), common pea (Pisum sativum), broad or faba bean (Vicia faba), cow pea (Vigna sinensis), common bean (P. vulgaris), mung bean (Phaseolus aureus), Lima bean (P. lunatus), and scarlet runner bean (P. multiflorus). The entire pod of the carob (Ceratonia siliqua) can be eaten and is similar to a candy because of the naturally large concentration of sugar that it contains.

The licorice (Glycyrrhiza glabra) is a perennial herb that is native to southern Europe and Asia and is now cultivated more widely. The rhizome of licorice is mostly used in the preparation of candy and to much smaller degrees to prepare medicinals, shoe polish, and to flavor tobacco.

Some species of legumes are important in agriculture as nitrogen-rich forages for domestic livestock. Species of forage legumes that are commonly cultivated in North America include alfalfa or lucerne (Medicago sativa), sweet clovers (Melilotus officinalis and M. alba), birds-foot trefoil (Lotus corniculatus), vetches (Vicia cracca and other species), and various species of clovers, including red clover (Trifolium pratense), white clover (T. repens), hop-clovers (T. agrarium and T. procumbens), and alsike clover (T. hybridum). Legumes are also used as a so-called "green manure" or soil conditioner which is grown and then ploughed into the ground to improve the soil quality in terms of organic matter and fixed nitrogen.

Other economic products obtained from legumes

Many tree-sized species in the legume family are valuable for their hard, durable timber. North American species are relatively minor in this respect, although the Kentucky coffee tree, black locust, and honey locust are used as lumber to some degree.

Some leguminous species of tropical hardwoods are highly prized for fine woodworking. Purpleheart (Peltogyne paniculata) is a very hard, durable, and strong wood found in northern South America which is a brownish color when first sawn but turns a spectacular purple after being exposed to the atmosphere for a while. This tropical hardwood is used to manufacture fine furniture and as a decorative inlay into other woods. Rosewoods also have hard, dark-purple woods that are widely sought after to manufacture fine furniture and other goods. Examples include Brazilian rosewood (Dalbergia nigra) and Asian rosewoods (D. latifolia and D. sissoo).

Various species of trees in the genus Acacia are also important sources of lumber, for example, A. melanoxylan and A. visco in Australia . Species of Albizia are also important timber trees.

The seeds of the mesquite (Prosopis juliflora) of the southwestern United States and Mexico are used as animal feed, while the wood is burned to manufacture a flavor-enhancing charcoal. Mesquite flavorings have become quite popular in recent years, and many foods are now seasoned with this plant, including potato and corn chips.

Sunhemp is a fiber obtained from Crotalaria juncea, a legume native to south Asia. This is an annual plant, grown mostly in the Indian subcontinent and used to manufacture twine, ropes, bags, and canvas.

Gums are plant compounds that are used as adhesives, to manufacture paints and candies, to prepare paper , and to manufacture certain medicines. Important gums are made from extracts of certain legume species including gum tragacanth from Astragalus gummifer, gum Arabic from Acacia senegal and A. stenocarpa, and tragasol from the carob (Ceratonia siliqua).

The barks of some species of acacias are sometimes used as sources of tannins, chemicals that are mostly used to manufacture leather from animal skins. Species used for this purpose include Acacia dealbata, A. decurrens, and A pycnantha, all native to Australia but also cultivated elsewhere.

Some important dyes are extracted from species in the legume family. One of the world's most important, natural dyes is indigo, extracted from the foliage of the indigo (Indigofera tinctoria) of south Asia and to a lesser degree from American indigo (I. suffruticosa) of tropical South America. Indigos are still cultivated widely for their dark-blue dye, although similar chemicals have been synthesized and are now widely available.

Other important natural dyes are obtained from the heartwood of several species of leguminous trees. Logwood (Haematoxylon campechianum) is a small, thorny tree native to Central America that is an important source of a dye known as hematoxylin, which has a deep, purple-red color, and can also be manufactured into a persistent black dye. The brazilette (H. brasiletto) is a source of a natural red dye as are brazilwood (Caesalpina brasiliensis) and sappanwood (C. sappan) of south Asia.

Derris or rotenone is a poisonous alkaloid that has long been used by indigenous peoples of Southeast Asia as arrow and fish poisons. Rotenone is now used widely as a rodenticide to kill small mammals and as an insecticide to kill pest insects. This chemical is mostly extracted from the plants Derris elliptica and D. malaccensis.

Shellac is now a relatively minor product, but until recently it was widely used for finishing wood and for manufacturing products such as phonograph records and electrical insulators. Shellac is derived from a sticky substance that is secreted by an Asian insect, Tachardia lacca. However, several species in the legume family are cultivated as hosts for the insect, including the pigeon pea (Cajanus cajan) and babul tree (Acacia arabica).

Legumes in horticulture

Some species of legumes are important in horticulture where they are typically grown for their beautiful flowers and sometimes as foliage plants. The scotch broom (Cytisus scoparius) is a green-stemmed, bushy shrub with attractive, yellow flowers. Gorse (Ulex europaeus) is also a shrub with spiny branches and bright yellow flowers. These shrubs are widely used in horticulture in temperate climates as are the North American trees, redbud, Kentucky coffee tree, and black and honey locust. Some non-native species that are used in horticulture in temperate climates of North America include species of laburnum such as Scotch laburnum (Laburnum alpinum) and common laburnum (L. anagyroides).

Many other leguminous trees and shrubs are grown as ornamentals in subtropical and tropical climates. Species cultivated in southern parts of the United States include the royal poinciana (Delonix regia) of Madagascar, the paradise poinciana (D. gilliesii) of South America, the tamarind (Tamarindus indica) of south Asia, and the silktree (Albizia julibrissin) and woman's tongue (A. lebbek) of south Asia.

Various species of garden lupines (Lupinus) are grown for their attractive, tall spikes of colorful flowers. Commonly grown species include L. polyphyllus and L. nootkatensis whose flowers are naturally colored blue but also occur in white, pink, red, and other floral cultivars.

Other legumes that are commonly grown in gardens include the Japanese wisteria (Wisteria floribunda), Chinese wisteria (W. sinensis), and related species. The sweet pea (Lathyrus odoratus) is also commonly grown as an attractive, climbing plant.

Legumes as weeds

Some species of legumes that are cultivated in agriculture or horticulture have become naturalized in semi-natural and natural habitats, and some of these are locally considered to be invasive weeds. Examples of these species include Scotch broom, gorse, garden lupines, vetches, and some other species. These are rarely considered important enough as weeds to be the specific targets of control programs.

One exception, however, is the kudzu vine (Pueraria lobata), native to Japan and introduced to the southeastern United States as a forage plant and for use in controlling erosion . This species is considered to be a serious, invasive weed in some places. Control methods for the kudzu include the use of herbicides and the excavation of its large, underground, roots.

A few species of legumes have foliage or seeds that can be extremely toxic to humans and domestic animals, and these may be actively controlled to reduce the risks of poisoning. The best North American examples of toxic legumes that are sometimes considered to be pests because they can poison livestock on rangelands are the locoweeds (Oxytropis spp., and to a lesser degree, Astragalus spp.). The precatory pea or rosary bean (Abrus precatorius) grows wild in subtropical and tropical climates and was introduced as an ornamental plant to south Florida where it is now naturalized. This species has small (less than 0.4 in [1 cm] long), very attractive, crimson-red seeds, with one jet-black spot at one end, but these are so toxic that a single one can kill a person if chewed. Precatory peas are sometimes used to make beautiful seed-necklaces, but these can be deadly in the hands of children.

Resources

books

Duke, J. A. Handbook of Legumes of World Economic Importance. New York: Plenum Press, 1981.

Hvass, E. Plants That Serve and Feed Us. New York: Hippocrene Books, 1975.

Judd, Walter S., Christopher Campbell, Elizabeth A. Kellogg, Michael J. Donoghue, and Peter Stevens. Plant Systematics: A Phylogenetic Approach. 2nd ed. with CD-ROM. Suderland, MD: Sinauer, 2002.

Klein, R.M. The Green World: An Introduction to Plants and People. New York: Harper and Row, 1987.

Bill Freedman

KEY TERMS

Bilateral symmetry

—In reference to flower shape, this indicates that a vertical sectioning of the flower will produce two halves with symmetric features.

Compound leaf

—A leaf in which the blade is separated into several or many smaller units, called leaflets, arranged along a central petiole or stalk known as a rachis.

Cultivar

—A distinct variety of a plant that has been bred for particular, agricultural or culinary attributes. Cultivars are not sufficiently distinct in the genetic sense to be considered to be subspecies.

Legume

—This is a type of fruit, also known as a pod, which is developed from a single ovary but contains multiple seeds and opens along a single seam when ripe.

Nitrogen fixation

—The conversion of atmospheric nitrogen gas (N2) to ammonia or an oxide of nitrogen. This process can occur biologically through action of the microbial enzyme, nitrogenase, or inorganically at high temperature and pressure.

Nitrogenase

—An enzyme synthesized by Rhizobium and some other microorganisms that is capable of cleaving the triple bond of nitrogen gas (N2), generating ammonia (NH3), a type of fixed nitrogen that plants can utilize in their nutrition.

Rhizome

—This is a modified stem that grows horizontally in the soil and from which roots and upward-growing shoots develop at the stem nodes.

Tendril

—A spirally winding, clinging organ that is used by climbing plants to attach to their supporting substrate. In the legume family, tendrils are derived from modified leaflets.

Weed

—Any plant that is growing abundantly in a place where humans do not want it to be.

LEGUMES

LEGUMES , a general name for plants of the family of Papilionaceae of the order Leguminae. In the Mishnah legumes are referred to as kitniyyot, a name derived from katan ("small"; cf. It.: leguma or minutia), because the seeds are usually small.

Though species with large seeds like pol ("broad bean," Vicia faba) belong to this family, at least in one source this species is not included among kitniyyot (Ḥul. 52a). Although in his Mishnah commentary (Kil. 2:2) Maimonides enumerates among kitniyyot only legumes, including the broad bean, in the Mishneh Torah he includes among them other species, such as rice, durra, poppy-seed and sesame (*Spices; Yad, Ḥameẓ u-Maẓẓah; 5:1). This definition of kitniyyot was taken over by other authorities, who went further and included among them many other edible seeds excluding cereals (wheat, barley, oats, etc.) which are classed as dagan ("corn") and regarded maize as a species of kitniyyot. This definition affected the laws of Passover, since among Ashkenazim kitniyyot are permitted them only in time of emergency. It should be noted that the Mishnah distinguishes between kitniyyot on the one hand and rice, durra, millet, and sesame on the other (Hal. 1:4). Thus kitniyyot originally referred only to legumes. Nowadays, a field in which legumes have been grown is considered most suitable for crop rotation with cereals. In ancient times this was not regarded as important and doubts arose whether legumes exhaust the soil more than wheat (bm 9:8; cf. bm 107a). It is to be noted that in recent years similar doubts have arisen. Legumes are richer in proteins than cereals but are not as easily digestible. They were mainly the food of the common people (see *Beans). A guest who prolonged his stay would be fed by his host with legumes (Tanh. B., Num. 156). A wife whose husband was obliged to provide her with food received four times as much wheat as legumes (Ket. 5:8), and this was probably the relation between the sown areas of cereals and kitniyyot.

Two species of legumes are mentioned in the Bible: adashim ("*lentils") and pol ("broad beans"). Lentils were the most important and one of the earliest plants in the region. In the Bible the term pol denotes only the broad bean but in rabbinic literature it was transferred by the addition of a denominative to other species too. Thus for instance pol ha-miẓri ("Egyptian bean") was cowpea, pol he-haruv ("carob bean") yard-long bean. Besides these legumes, two species of Lupinus are mentioned in rabbinic literature: turmus – Lupinus termis, and polaslos ("yellow lupine") – Lupinus luteus (Kil 1:3). The lupine was a cheap food and thus of importance for the poor. Because of their bitterness, the seeds had to be soaked in water or cooked a number of times, and the liquid poured off (Ber. 38b, et al.). At least two species of the genus Lathyrus were grown: tofaḥ ("grass pea") – Lathyrus sativus, and porkedan ("red grass pea") – Lathyrus cicera, both of which were considered one species as regards *mixed species (kilayim; Kil. 1:1). These names may include also other species of the genus Lathyrus, some of which grow wild in Israel and are sown at times by the fellahin. Some are of the opinion that asisiyyot or asasiyyot (Tosef., Shab. 3:1; tj, Shab. 3:1, 5d) are also a species of Lathyrus. Today these are mainly grown as fodder, except for grass pea which is used for human consumption. The seeds are soaked in water and crushed; the taste is similar to that of broad beans (Tosef., Ter. 6:11).

Two species of vetch are mentioned in the Mishnah: sappir ("French vetch") – Vicia narbonensis, and karshinah ("bitter vetch") – Vicia ervilia, the latter used for fodder. Sappir is considered to be of the same species as pol for the law of kilayim (Kil. 1:1), and the plants and seeds of these two species of vetch are indeed very similar. According to the Jerusalem Talmud (tj, Kil. 1:1, 27a), a tanna named Hillel b. Valas had a Hebrew-Aramaic dictionary, as well as, apparently, a Hebrew-Latin-Greek one, of plant names in which sappir was identified with pisonah, the Latin pisum which is the garden pea, Pisum sativum. This identification is doubtful and there are no other references in the Mishnah and Talmud to the growing of this pea. The Mishnah mentions once a legume she'u'it which is considered the same species as pol ha-lavan ("white beans"; Kil. 1:1). In R. Hillel's dictionary of plants she'u'it was identified with pesilta by which is meant the nile cowpea, Vigna nilotica, and pol ha-lavan with hyacinth bean, Dolichos lablab. In modern Hebrew the name she'u'it is used for the genus Phasoleus. This botanical genus originated in America, however, and was unknown to the ancients.

A valuable plant was the chick-pea, Cicer arietinum, called ḥamiẓ. This is mentioned once in the Bible (Isa. 30:24). It was called ḥamiẓ because of the vinegary taste of the young seeds and the pod. The Mishnah calls it אֲפוּנִים (afunim, sing. אָפוּן, afun), apparently from אַפּוֹן (appon; "small nose"), because it has a projection like a small nose on the round seed. These are frequently mentioned in rabbinic literature, a number of species being grown: large and small (Kil. 3:2), light and dark (tj, Dem. 2:1, 22c). The Mishnah notes that it is a summer plant (Shev. 2:8). This is a decisive proof against the view of those who identify the afunim with garden peas which are definitely winter plants (though this latter identification has been accepted in modern Hebrew). Today chick-pea is especially popular among Oriental Jews, who prepare from it a piquant dish called ḥumus. One of the most valuable legumes was the plant tiltan (a name used today for clover), fenugreek, Trigonella foenumgraecum. Its leaves were grown for fodder and its seeds eaten when green or hard (Ma'as. Sh. 2:3; Tosef., ibid. 2:1). Its seeds are similar to those of the carob, and fenu-greek was sometimes adulterated with carob seeds (Tosef., bk 7:8). Although tiltan is not mentioned in the Bible the Talmudstates that Joshua made a number of regulations concerningit (BK 80b–81a). Nowadays it is grown chiefly for fodder, although the Yemenites grind the seeds to prepare a pungent sauce called ḥilbah.

bibliography:

Loew, Flora, 2 (1924), 410–4; H.N. and A.L. Moldenke, Plants of the Bible (1952), 34f., 254; J. Feliks, Ha-Ḥakla'ut be-Ereẓ Yisrael bi-Tekufat ha-Mishnah ve-ha-Talmud (1963), 178–80, 273–5; idem, Kilei Zera'im ve-Harkavah (1967), 33–43, 71–89, 194f., 230–2.

[Jehuda Feliks]

legume Member of the pea family of flowering plants, including many trees, shrubs, vines and herbs whose roots bear nodules that contain nitrogen-fixing bacteria. The fruit is typically a pod (legume) containing a row of seeds. Important food species include the pea, runner bean, soya bean, lentil, broad bean, kidney bean, and haricot bean. See also nitrogen cycle; nitrogen fixation; root nodule