The Overstory
The Overstory #191--Edible Leaves
11th July, 2007
The Overstory #191--Edible Leavesby Franklin W. Martin, Ruth M. Ruberté, and Laura S. Meitzner
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.
NUTRITIONAL ASPECTS
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.
FRUIT TREES
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
<publications@spc.int> ]
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: <books@echonet.org>; web: <http://www.echobooks.org/> ]