Overstory #191 - Edible Leaves
The place of green leaves in the diet
Green leaves are not equally appreciated in all parts of the tropics and thus play a varied role in the diets of distinct peoples. East and West Africans make frequent use of green vegetables. In parts of Latin America, green leaves are considered food for animals, although local or weedy species may be added to the cooking pot in times of food shortage or in remote regions. In the temperate zone, lettuce is an essential item in salads and is eaten uncooked. Crucifers of many kinds are also well known and used worldwide. The place of green vegetables in the diet is largely a matter of culture, training, and habit.
The role of green leaves in the diet may also be considered by noting how the green food is used. Probably the most common use in all parts of the world is as a boiled vegetable. By boiling, potential pathogens are thus eliminated, sometimes poisonous or irritating substances are neutralized, and spoilage is brought to a halt. Nevertheless, this technique reduces the leaf to a limp and soggy mass, which may not always be appetizing. Some nutrients may be destroyed by heating while others may be leached out. As a general rule, cooking should be as brief as possible. Some leaves may contain mucilaginous substances, which are often, but not always, appreciated. Frying leaves in oil or enveloped in batter preserves some of their unique characteristics and maintains their texture.
Raw vegetables add novel touches and serve to vary and make interesting the meal. For example, many green leaves may be eaten raw, but some knowledge and judgment must be applied. Xanthosoma brasiliense leaves contain irritating calcium oxalate crystals, easily removed by boiling. As another example, cooking also inactivates dangerous hydrocyanic glycosides in the leaves of cassava (Manihot esculenta).
The drying of green leaves and their preservation as powder is a common practice in Africa and elsewhere. Although some of the food value is lost in the drying process, this method permits storage of easily perishable leaves, making them convenient for use in the kitchen or into the dry season when greens are scarce. Drying merits more investigation, for it is a simple technique that can be widely used throughout the tropics, especially using easily constructed and efficient solar dryers.
Many diets of the tropical zones are based on starchy staples supplemented, when possible, by foods high in protein. Green-leaved vegetables offer enrichment to such diets and are useful as regulators of the digestive tract. Leaves are the most physiologically active parts of the living plant, and as such are usually rich in vitamins and minerals. Their carbohydrate content is usually insignificant. Although leaves are often not rich sources of protein, some contain sufficient amounts to supplement an otherwise inadequate starchy diet. Greens also contain high amounts of important antioxidants, which serve a protective function against certain diseases. Finally, leaves offer non-nutritional benefits, such as making other foods more appealing, providing a dependable source of food for the family, and adding to household income.
Green leaves have a role in preventing or treating the malnourishment present in many tropical areas where leaves grow abundantly, often with little effort in their cultivation. Three considerations in addition to taste preferences ought to influence the choice of foods for a normal diet the caloric needs, the protein requirement, and the need for vitamins and minerals. Leafy vegetables are particularly important with respect to the latter requirement, adding vitamins and minerals quite out of proportion to their weight. Indeed, no other class of edible plants is equally rich in these nutrients. The diet should include modest amounts of green leaves every day.
Tropical trees with edible green leaves
The deep emotions inspired by trees possibly result from their many uses and benefits to people. From trees the physical necessities of life are taken wood for shelter and for cooking, bark and fiber to be pounded or to be woven into cloth, both sweet and starchy fruits, nuts, and rich sources of edible oils, liquids (not common) to be used as beverages with or without fermentation, or to be evaporated to yield sugar. In addition, trees fill aesthetic needs. They are often graceful and pleasing to the eye or give a sense of permanence by their sheer size. They often outlive humans, and because many grow so slowly, it is said that one must have faith to plant trees.
In spite of their abundance and their multiplicity of uses, trees are seldom thought of as sources of edible green leaves. In fact, very few trees of the temperate zone are utilized in that fashion. In some areas of the tropics, however, the edible qualities of the leaves of certain trees are much appreciated. It is common, for example, to see the gnarled living fence posts of various species that are so shaped because their leaves are continually removed for animal fodder. The harvesting of the edible crop maintains the form of the hedge. Some type of pruning of trees bearing edible leaves is always desirable to keep the leaves within easy reach.
Throughout the tropics there are a very large number of trees that bear edible fruits. It is not difficult to make a list of 300 species, and in addition many more of minor importance are found in restricted areas. Nevertheless, the majority of the fruits and nuts of the tropics come from a very limited number of species. These species found throughout the tropics are those that merit special attention here.
The leaves of citrus fruits (Rutaceae) often contain essential oils and flavonoids that impart characteristic pungent odors and tastes. These leaves are not eaten. Several minor species of the family do produce edible leaves.
The leaves of the banana (Musa sp. and hybrids, Musaceae), once they have emerged from the pseudostem, toughen up rapidly and are more suitable for wrapping foods than to be eaten themselves. Nevertheless, within the pseudostem the developing leaves are much more tender, and can be eaten either raw or cooked. This portion is often called the heart. To extract the heart the trunk can easily be opened with a sharp machete. In addition to the heart, the flower bud of the banana can be eaten after boiling. The soft portions near the base of the flower bracts are eaten as are those of the bracts of globe artichokes.
Fruit-bearing trees of the family Anacardiaceae also bear edible leaves. Anacardium occidentale L., for example, is the source of the cashew nut and of the cashew apple, the fleshy peduncle of the true fruit. It is a species especially adapted to poor soils and dry areas. Although native to Brazil, it is widely planted throughout the tropical world, frequently in coastal areas, as a source of nuts for the international trade. Since the shell of the nut contains an irritating oil similar in structure and effects to that of poison ivy, the raw nuts should not be bitten into until they are roasted. The young leaves are commonly cooked in Southeast Asia but are too astringent for regular use.
Mangoes (Mangifera indica L.), now so displaced from their native habitats in India and Southeast Asia, are found everywhere throughout the tropics. Most mangoes perform best in a moderately dry climate. New leaves are produced in several vigorous flushes of growth each year, usually beginning with the rainy season. These young leaves are frequently rose-colored or bronzed with anthocyanin. On cooking them, the anthocyanin is boiled out, leaving the leaves pale green. The cooked leaves tend to hold their shape and texture, and present an attractive appearance. The flavor is more or less resinous, and will not agree with every palate. The leaves of distinct varieties vary in their suitability. Some study to determine the best varieties as sources of edible leaves would be desirable.
A number of species of Spondias bear edible fruits, and it is probable that leaves of all species are edible. Young leaves of S. cytherea Sonn. (ambarella) are eaten raw or cooked. The leaves of S. purpurea L. (red mombin) are eaten raw, and those of S. pinnata Kurz (an-ira) are cooked.
Leaves of the soursop (Annona muricata L., Annonaceae) are edible. This and its many relatives are mostly small trees, some adapted to dry and others to wet forests. On cooking the soursop leaf, a good texture is retained. The cook pot emits a rich odor. Cooked leaves are slightly bitter, and do not have much flavor.
One of the rarest of tropical fruits in the western hemisphere, the durian (Durio zibethinus Murray, Bombacaceae) of Southeast Asia. This is a tall tree from which foliage cannot easily be taken, but the young leaves of durian are sometimes eaten after cooking. Other species of Durio also bear edible fruits, and certainly the leaves of some of these must be edible.
It is not surprising that the fruit-bearing species of Euphorbiaceae also bear edible leaves, as this is so typical of many members of the family. One of the best known is the bignay (Antidesma bunius (L.) Sprengel) from Southeast Asia. On cooking, the young leaves turn an unattractive brown but retain their texture. The flavor is slightly sour, but otherwise similar to artichoke.
Two species of Phyllanthus, another genus of Euphorbiaceae, bear edible fruits and leaves. The Otaheite gooseberry or grosella (P. acidus (L.) Skeels) produces large quantities of yellow, waxy, scalloped-edged fruits. Its cooked young leaves are neutral or mild in flavor, but somewhat fibrous. P. emblica L. (emblic) is not as common. The round, greenish, angled fruits are high in vitamin C. The leaves of this species, though edible, are very small. On cooking there is little odor, but the cooking water becomes an unappetizing suspension of yellowish particles. The flavor is extremely bitter and would appeal to very few people.
The common tamarind (Tamarindus indica L., Leguminosae) is a tropical tree from Africa now widely distributed, and particularly well known in India. Once cooked, the young leaves lose their color. The cooking odor is not pronounced. The flavor is agreeably sour and similar to that of the fruit. Thus, this type of leaf is best cooked with other, less flavorful vegetables. Both the leaves and flowers are eaten fresh in salads or cooked in curries, soups, and stews.
The family Moraceae furnishes several species with edible leaves. Many wild figs (Ficus sp.) bear edible leaves and shoots. Some species of Artocarpus, the genus of breadfruit and jackfruit, yield young leaves that are good to eat. Perhaps the most important fruit species with edible leaves is the common mulberry, Morus alba L., a rapidly growing tree from China that is more common in temperate than in tropical zones. Nevertheless, there are varieties that perform well even at sea level in the humid tropics. Selected varieties bear very excellent fruits. This and the variety indica are the sources of leaves traditionally grown as feed for silkworms in China. All parts of the tree have medicinal uses in China. The young leaves are edible and are consumed principally by nursing mothers. On cooking, the young leaves become very soft but retain their color. The flavor is mild. The fine pubescence may be slightly unpleasant.
The Rosaceae family includes a number of tropical fruits, but few species have leaves which are eaten. An exception is the raspberry, Rubus rosaefolius Smith, introduced from the Himalayas but now widely distributed and excessively weedy in some high rainfall areas. The foliage is light green, and the berry red on maturity, with little flavor. Red young leaves of rose bushes (Rosa spp.) are edible raw or cooked.
Among the many fruits of the Sapotaceae, one of the best is the sapodilla or nispero (Manilkara zapota (L.) van Royen). It is very common in tropical America, especially Mexico and Central America, where it serves as a source of chicle for the manufacture of chewing gum. The leaves contain a poisonous alkaloid; only the very young leaves are considered edible.
Papayas, Carica papaya L. (Caricaceae), are grown chiefly for their fruits. The interior of the stem is soft, and may be eaten raw. Dried leaves are used as a tobacco substitute, and can also be beaten in water to form a soap substitute. The leaves may be cooked as a green vegetable. They should not be eaten raw because of the possible danger from both the alkaloid carpaine and the enzyme papain. As a precaution, older leaves should be thoroughly boiled, changing the water at least twice. Younger leaves are not harmful. Flowers are also cooked and eaten, generally with the leaves. Upon cooking, the leaves have a pleasant chartreuse color and retain their form and texture. The cooked leaves have a strong, bitter taste that is disagreeable to some people. In addition, they have a distinctive flavor reminiscent of asparagus. The tender petioles may be eaten, but are more bitter than the blades. Papaya leaves are more appropriately served in stews than as a separate dish.
The leaves of coffee, Coffea arabica L. (Rubiaceae), are edible. On cooking, they have a strong brown color, a good texture, and a rather neutral flavor with only a touch of bitterness.
Sources of information on edible leaves
Surprisingly little has been written on tropical edible leaves, considering their importance in the diet. The published information available, often repetitive and seldom complete, has generally been hidden in more general publications concerning tropical gardening or useful plants. Recent years, however, have seen an increase in the efforts to investigate the role of greens in the diet. Both the classic references and newer publications on nutrition are of value. The best single source of information which can be recommended for the principal species is Ochse and Bakhuizen van den Brink (1931). Seeds and plant materials may be difficult to find, although some species are offered in commercial seed catalogs; some local and regional seedbanks also now include leaf species. Facciola (1998) is the essential resource for the gardener seeking information on varieties and looking for planting materials.
Vegetables of the Dutch East Indies (Ochse and Bakhuizen van den Brink 1931). One of the richest sources of green-leaved vegetables is Indonesia. As a crossroads of Southeast Asia, practically all edible plants of the surrounding regions have been introduced and many have become part of the diet. This volume is one of the authoritative works in this field. First published in 1891, it was translated to English in 1931. Principally pot herbs and side dishes are covered, but tubers, bulbs, rhizomes, and spices are also mentioned. The problem may be obtaining a copy; it has become a collectors' item, difficult to even borrow.
Tropical Leaf Vegetables in Human Nutrition (Oomen and Grubben 1978). For the health promoter in tropical countries, we know of no more practical handbook to assist in evaluating, growing, and using leaves in nutrition programs. The authors offer a practical perspective on the nutritive value and usages of greens and describe the cultivation of major crops (hot and cool season annuals and perennials). Ideas for nutrition education and several detailed recipes from six countries are helpful to the field worker. There are excellent pictures on every page.
The Leaves We Eat (Bailey 1992). This book provides information on a wide variety of Pacific green leafy vegetables. The book is for those working in agriculture, health and nutrition in the Pacific islands, though its usefulness extends throughout the tropics. The text is rich in useful information, illustrations and color photographs. [Publisher Secretariat of the Pacific Community, BP D5, Noumea Cedex 98848, New Caledonia; Tel +687 262000; Fax + 687 263818; Website http//www.spc.int; For purchasing the book contact email@example.com.
Cornucopia A Source Book of Edible Plants II (Facciola 1998). This is an indispensable guide to further information and germplasm sources for over 3000 species, including over 800 species with edible leaves and leafy shoots. Extensive, detailed varietal descriptions are included for common crops, but little-known and localized species are also included. Common names, listings of edible portions, and thorough indices make this resource even more valuable. In the past it was extremely difficult to locate planting materials of many plants discussed here--not anymore. [Publisher Kampong Publications, 1870 Sunrise Drive; Vista, California 92084, USA]
Edible Leaves of the Tropics, Third Edition (Martin, Ruberté, and Meitzner 1998). This book describes familiar and exotic plants with edible leaves, discussing their origin, growth habit, cultivation guidelines, nutritional value, preparation. multiple uses, and cautions. A comprehensive appendix lists over 1500 additional species reported to have edible leaves. The new edition includes expanded information on the most promising plants tested over a wide range of conditions and tastes, as well as updates on food value and resources on this topic. It is useful for all those working with tropical plants, as well as those involved in community nutrition or agricultural development. [Publisher ECHO, 17391 Durrance Rd., N. Ft. Myers, FL 33917, USA; Tel 239-543-3246; Fax 239-543-5317; E-mail firstname.lastname@example.org; web http//www.echobooks.org
Bailey, J.M. 1992. The leaves We Eat. South Pacific Commission, Noumea, New Caledonia. 97 pp.
Facciola, S. 1990. Cornucopia A Source Book of Edible Plants. Kampong Publications, Vista, California. 678 pp.
Ochse, J.J., and R.C. Bakhuizen van den Brink. 1931. Vegetables of the Dutch East Indies. Dept. of Agriculture, Industry and Commerce of the Netherlands. East Indies, Buitenzorg. 1004 pp.
Oomen, H.A.P.C. and G.J.H. Grubben. 1977. Tropical Leaf Vegetables in Human Nutrition. Comm. 69. Royal Tropical Institute, Amsterdam. 136 pp.
This article is excerpted with the gracious permission of the authors and publisher from
Martin F.W., R.M. Ruberté, and L.S. Meitzner. 1998. Edible Leaves of the Tropics, Third Edition. ECHO, North Fort Myers, Florida, USA.
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About the authors
Franklin W. Martin is an internationally renowned authority on tropical food plants and food self-sufficiency. He is retired from the USDA Tropical Research Station in Puerto Rico. He now lives in Florida and shares his expertise with many, including the nearby Educational Concerns for Hunger Organization (ECHO), 17430 Durrance Road, North Fort Myers, FL, USA; Tel 239-543-3246; Fax 239-543-5317; Email email@example.com; Web http//www.echonet.org.
Ruth M. Ruberté and Franklin W. Martin have collaborated on numerous books, including Perennial Edible Fruits of the Tropics, Edible Leaves of the Tropics, Techniques and Plants for the Tropical Subsistence Farm, Survival and Subsistence in the Tropics, and Multipurpose Palms You Can Grow Twenty of the World's Best.
Laura S. Meitzner Yoder has worked with crop biodiversity, land claims, and forest use in tropical America and Asia. She has worked in rural development with the Educational Concerns for Hunger Organization (Florida, USA) and Mennonite Central Committee (Papua, Indonesia). She co-authored Edible Leaves of the Tropics (Third Edition), Amaranth to Zai Holes Ideas for Growing Food under Difficult Conditions, and the technical newsletter ECHO Development Notes. She holds a Masters in International Agriculture and Rural Development from Cornell University, and her current project is completing a PhD on land and forest claims in East Timor with the Yale University School of Forestry and Environmental Studies.
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