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Yam is the common name for some plant species in the genus ''
Dioscorea ''Dioscorea'' is a genus of over 600 species of flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may re ...
'' (family
Dioscoreaceae Dioscoreaceae () is a family (biology), family of monocotyledonous flowering plants, with about 715 known species in nine genus, genera. The best-known member of the family is the yam (vegetable), yam (some species of ''Dioscorea''). The APG syst ...
) that form edible
tuber Tubers are enlarged structures used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing season, and ...
s. Yams are
perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and incl ...
herbaceous Herbaceous plants are vascular plants that have no persistent wood, woody stems above ground, including many perennial plant, perennials, and nearly all Annual plant, annuals and Biennial plant, biennials. Definitions of "herb" and "herbaceous" ...
vine A vine (Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation ...

vine
s cultivated for the consumption of their
starch Starch or amylum is a polymeric A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance ...
y tubers in many
temperate In geography Geography (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its populati ...
and
tropical The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S; these latitudes correspond to ...

tropical
regions, especially in West Africa, South America and the Caribbean, Asia, and
Oceania Oceania (, , ) is a geographic region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Eart ...

Oceania
. The tubers themselves, also called "yams", come in a variety of forms owing to numerous
cultivar A cultivar is a type of plant that people have bred for desired traits, which are reproduced in each new generation by a method such as grafting, tissue culture or carefully controlled seed production. Most cultivars arise from purposeful human ...
s and related species. Yams were independently domesticated on three different continents:
Africa Africa is the world's second-largest and second-most populous continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', ...

Africa
(''
Dioscorea rotundata ''Dioscorea cayennensis'' subsp. ''rotundata'', commonly known as the white yam, West African yam, Guinea yam, or white ñame, is a subspecies of yam (vegetable), yam native to Africa. It is one of the most important cultivated yams. Kokoro (veget ...
''), Asia (''
Dioscorea alata ''Dioscorea alata'', also known as purple yam, ube (), or greater yam, among many other names, is a species of yam (a tuber). The tubers are usually a vivid Violet (color), violet-purple to bright Lavender (color), lavender in color (hence the c ...

Dioscorea alata
''), and the Americas (''
Dioscorea trifida ''Dioscorea trifida'' is a species of flowering plant in the family Dioscoreaceae. It is a species of Yam (vegetable), yam (genus ''Dioscorea''). It is native to the Caribbean and Central and South America. Its many common names include Indian yam ...

Dioscorea trifida
'').


Etymology

The name "yam" appears to derive from Portuguese ''inhame'' or
Canarian Canary Islanders, or Canarians ( es, canarios), are a Romance peoples, Romance people and subgroup of the Spaniards. They are indigenous to the Canary Islands, an Autonomous communities of Spain, autonomous community of Spain near the coast of West ...
(Spain) ''ñame'', which derived from
West African languages Image:Compass Rose English West.svg, 250px, A compass rose with west highlighted in black West is one of the four cardinal directions or points of the compass. It is the opposite direction from east, and is the direction in which the sun sets. E ...
during trade. Although in both languages, this name is commonly referred to the plant
taro ''Colocasia esculenta'' is a tropical plant grown primarily for its edible corm A corm, bulbo-tuber, or bulbotuber is a short, vertical, swollen underground plant stem '' has lost its leaves, but is producing adventitious rootsImportant ...

taro
(''Colocasia esculenta'') from the genus
Colocasia ''Colocasia'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circ ...
, as opposed to
Dioscorea ''Dioscorea'' is a genus of over 600 species of flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may re ...
. The main derivations borrow from verbs meaning "to eat". True yams have various
common names Common may refer to: Places * Common, a townland in County Tyrone County Tyrone (; ) is one of the thirty-two traditional Counties of Ireland, counties of Ireland, one of the six Counties of Northern Ireland, counties of Northern Ireland an ...
across multiple world regions. In some places, other (unrelated) root vegetables are sometimes referred to as "yams", including: * In the United States,
sweet potatoes The sweet potato or sweetpotato (''Ipomoea batatas'') is a dicotyledon The dicotyledons, also known as dicots (or more rarely dicotyls), are one of the two groups into which all the flowering plant The flowering plants, also known as Angi ...

sweet potatoes
(''
Ipomoea ''Ipomoea'' () is the largest genus in the flowering plant Family (biology), family Convolvulaceae, with over 600 species. It is a large and diverse group, with common names including morning glory, Ipomoea aquatica, water convolvulus or kangkun ...

Ipomoea
batatas''), especially those with orange flesh, are often referred to as "yams" *In Australia, the tubers of the ''
Microseris lanceolata ''Microseris lanceolata'' is an Australian alpine herb with yellow flowers and one of three plants known as murnong or yam daisy along with ''Microseris scapigera'' and ''Microseris walteri.'' The plant is found in southern parts of Australia, i ...
'', or yam daisy, were a staple food of
Aboriginal Australians Aboriginal Australians are the various Indigenous peoples Indigenous peoples, also referred to as first peoples, first nations, aboriginal peoples, native peoples (with these terms often capitalized when referred to relating to specific ...
in some regions. * In New Zealand, (''Oxalis tuberosa'') is typically referred to as "yam". *In
Malaysia Malaysia ( ; ) is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the geographical southeastern subregion of Asia, consisting of the regions ...

Malaysia
,
Singapore Singapore (), officially the Republic of Singapore, is a sovereign state, sovereign island city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, bor ...

Singapore
and ,
taro ''Colocasia esculenta'' is a tropical plant grown primarily for its edible corm A corm, bulbo-tuber, or bulbotuber is a short, vertical, swollen underground plant stem '' has lost its leaves, but is producing adventitious rootsImportant ...

taro
(''Colocasia esculenta'') is referred to as "yam". *In Africa, South and Southeast Asia as well as the tropical Pacific islands ''
Amorphophallus paeoniifolius ''Amorphophallus paeoniifolius'', the elephant foot yam or whitespot giant arum, is a tropical tuber crop grown primarily in Africa, South Asia, Southeast Asia and the tropical Pacific islands. Because of its production potential and popularity ...
'' is grown and known as "elephant foot yam".


Description

A
monocot Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one Embryo#Plant embryos, embryonic leaf, or cotyledon. The ...
related to lilies and grasses, yams are vigorous
herbaceous Herbaceous plants are vascular plants that have no persistent wood, woody stems above ground, including many perennial plant, perennials, and nearly all Annual plant, annuals and Biennial plant, biennials. Definitions of "herb" and "herbaceous" ...
vine A vine (Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation ...

vine
s providing an edible
tuber Tubers are enlarged structures used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing season, and ...
. They are native to Africa, Asia, and the Americas. Some yams are also
invasive plant Invasive may refer to: * Invasive (medical) procedure * Invasive species * Invasive observation, especially in reference to surveillance Surveillance is the monitoring of behavior, activities, or information for the purpose of information gath ...
s, often considered a "
noxious weed A noxious weed, harmful weed or injurious weed is a weed A weed is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that we ...
", outside cultivated areas. Some 870 species of yams are known, and 95% of these crops are grown in Africa. Yam plants can grow up to in length and high. The tuber may grow into the soil up to deep. The plant disperses by seed. The edible tuber has a rough skin that is difficult to peel but readily softened by heating. The skins vary in color from dark brown to light pink. The majority of the vegetable is composed of a much softer substance known as the "meat". This substance ranges in color from white or yellow to purple or pink in mature yams.


Cultivation

Yam crop begins when whole seed tubers or tuber portions are planted into mounds or ridges, at the beginning of the rainy season. The crop yield depends on how and where the sets are planted, sizes of mounds, interplant spacing, provision of stakes for the resultant plants, yam species, and tuber sizes desired at harvest. Small-scale farmers in West and Central Africa often intercrop yams with cereals and vegetables. The seed yams are perishable and bulky to transport. Farmers who do not buy new seed yams usually set aside up to 30% of their harvest for planting the next year. Yam crops face pressure from a range of insect pests and fungal and viral diseases, as well as
nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...

nematode
. Their growth and dormant phases correspond respectively to the wet season and the dry season. For maximum yield, the yams require a humid tropical environment, with an annual rainfall over 1500 mm distributed uniformly throughout the growing season. White, yellow, and water yams typically produce a single large tuber per year, generally weighing . Despite the high labor requirements and production costs, consumer demand for yam is high in certain subregions of Africa, making yam cultivation quite profitable to certain farmers.


Major cultivated species

Many cultivated species of ''Dioscorea'' yams are found throughout the humid tropics. The most economically important are discussed below. Non-''
Dioscorea ''Dioscorea'' is a genus of over 600 species of flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may re ...
'' tubers that were historically important in Africa include '''' (the Hausa potato) and ''
Plectranthus esculentus ''Coleus esculentus'', synonym A synonym is a word, morpheme A morpheme is the smallest meaningful lexical item in a language. A morpheme is not a word. The difference between a morpheme and a word is that a morpheme bound and free morpheme ...
'' (the Livingstone potato); these two tuber crops have now been largely displaced by the introduction of
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names) is a woody shrub A shrub (often called a bush) is a small- to medium-sized perennial A perennial plant or simply perennial is a pla ...

cassava
.


''D. rotundata'' and ''D. cayennensis''

''
Dioscorea rotundata ''Dioscorea cayennensis'' subsp. ''rotundata'', commonly known as the white yam, West African yam, Guinea yam, or white ñame, is a subspecies of yam (vegetable), yam native to Africa. It is one of the most important cultivated yams. Kokoro (veget ...
'', the white yam, and '' D. cayennensis'', the yellow yam, are native to Africa. They are the most important cultivated yams. In the past, they were considered as two separate species, but most taxonomists now regard them as the same species. Over 200 varieties between them are cultivated. White yam tuber is roughly cylindrical in shape, the skin is smooth and brown, and the flesh is usually white and firm. Yellow yam has yellow flesh, caused by the presence of carotenoids. It looks similar to the white yam in outer appearance; its tuber skin is usually a bit firmer and less extensively grooved. The yellow yam has a longer period of vegetation and a shorter dormancy than white yam. The
Kokoro is a novel by the Japanese author Natsume Sōseki , born , was a Japanese Japanese may refer to: * Something from or related to Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep re ...
variety is important in making dried yam chips. They are large plants; the vines can be as long as . The tubers most often weigh about each, but can weigh as much as . After 7 to 12 months' growth, the tubers are harvested. In Africa, most are pounded into a paste to make the traditional dish of "pounded yam", known as Iyan.


''D. alata''

'''', called "white yam", winged yam, water yam, and purple yam (not to be confused with the Okinawan purple "yam", which is a
sweet potato The sweet potato or sweetpotato (''Ipomoea batatas'') is a dicotyledon The dicotyledons, also known as dicots (or more rarely dicotyls), are one of the two groups into which all the flowering plant The flowering plants, also known as Angi ...

sweet potato
), was first cultivated in Southeast Asia. Although not grown in the same quantities as the African yams, it has the largest distribution worldwide of any cultivated yam, being grown in Asia, the Pacific islands, Africa, and the West Indies. Even in Africa, the popularity of water yam is second only to white yam. The tuber shape is generally cylindrical, but can vary. Tuber flesh is white and watery in texture. ''Uhi'' was brought to Hawaii by the early Polynesian settlers and became a major crop in the 19th century when the tubers were sold to visiting ships as an easily stored food supply for their voyages.


''D. polystachya''

'''', Chinese yam, is native to
China China (), officially the People's Republic of China (PRC; ), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere ...

China
. The Chinese yam plant is somewhat smaller than the African, with the vines about long. It is tolerant to frost and can be grown in much cooler conditions than other yams. It is also grown in
Korea Korea is a region In geography, regions are areas that are broadly divided by physical characteristics (physical geography), human impact characteristics (human geography), and the interaction of humanity and the environment (environmental ...

Korea
and
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...

Japan
. It was introduced to
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
in the 19th century, when the
potato The potato is a starch#Food, starchy tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial plant, perennial in the nightshade family Solanaceae. Wild potato species can be found thro ...

potato
crop there was falling victim to disease, and is still grown in France for the Asian food market. The tubers are harvested after about 6 months of growth. Some are eaten right after harvesting and some are used as ingredients for other dishes, including noodles, and for traditional medicines.


''D. bulbifera''

'' D. bulbifera'', the air potato, is found in both Africa and Asia, with slight differences between those found in each place. It is a large vine, or more in length. It produces tubers, but the
bulb In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the A ...

bulb
ils which grow at the base of its leaves are the more important food product. They are about the size of potatoes (hence the name "air potato"), weighing from . Some varieties can be eaten raw, while some require soaking or boiling for detoxification before eating. It is not grown much commercially since the flavor of other yams is preferred by most people. However, it is popular in home vegetable gardens because it produces a crop after only four months of growth and continues producing for the life of the vine, as long as two years. Also, the bulbils are easy to harvest and cook. In 1905, the air potato was introduced to Florida and has since become an
invasive species An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
in much of the state. Its rapid growth crowds out native vegetation and it is very difficult to remove since it can grow back from the tubers, and new vines can grow from the bulbils even after being cut down or burned.


''D. esculenta''

'' D. esculenta'', the lesser yam, was one of the first yam species cultivated. It is native to Southeast Asia and is the third-most commonly cultivated species there, although it is cultivated very little in other parts of the world. Its vines seldom reach more than in length and the tubers are fairly small in most varieties. The tubers are eaten baked, boiled, or fried much like potatoes. Because of the small size of the tubers, mechanical cultivation is possible, which along with its easy preparation and good flavor, could help the lesser yam to become more popular in the future.


''D. dumetorum''

'' D. dumetorum'', the bitter yam, is popular as a vegetable in parts of West Africa, in part because their cultivation requires less labor than other yams. The wild forms are very toxic and are sometimes used to poison animals when mixed with bait. It is said that they have also been used for criminal purposes.


''D. trifida''

'''', the cush-cush yam, is native to the
Guyana Guyana ( or ), officially the Cooperative Republic of Guyana, is a country on the northern mainland of South America and the capital city is Georgetown Guyana, Georgetown. Guyana is bordered by the Atlantic Ocean to the north, Brazil to the ...

Guyana
region of South America and is the most important cultivated New World yam. Since they originated in tropical
rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapevine Religi ...

rainforest
conditions, their growth cycle is less related to seasonal changes than other yams. Because of their relative ease of cultivation and their good flavor, they are considered to have a great potential for increased production.


Wild taxa


''D. hirtiflora'' subsp. ''pedicellata''

'' Dioscorea hirtiflora'' subsp. ''pedicellata'', lusala, busala or lwidi, is native to
Tropical Africa Although tropical Africa is mostly familiar to the West for its rainforests, this biogeographic realm of Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 ...
. It is widely harvested and eaten in Southern Zambia where it grows in open forest areas. In Southern Zambia, it is an important addition to the March–September diets of almost all, and income of over half of rural households. Research on propagation of this subspecies to alleviate the threat from wild harvest has been successful.


''D. japonica''

Dioscorea japonica known as East Asian mountain yam, yamaimo, or Japanese mountain yam, is a type of yam (Dioscorea) native to Japan (including Ryukyu and Bonin Islands), Korea, China, Taiwan, and Assam. Dioscorea japonica is used for food. Jinenjo, also called the wild yam, is a related variety of Japanese yam that is used as an ingredient in soba noodles.


Harvesting

Yams in
West Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 17 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, Mauritania ...

West Africa
are typically harvested by hand using sticks, spades, or diggers. Wood-based tools are preferred to metallic tools as they are less likely to damage the fragile tubers; however, wood tools need frequent replacement. Yam harvesting is labor-intensive and physically demanding. Tuber harvesting involves standing, bending,
squatting Squatting is the action of occupying an abandoned or unoccupied area of land or a building, usually residential, that the squatter does not own, rent or otherwise have lawful permission to use. The United Nations The United Nations ( ...
, and sometimes sitting on the ground depending on the size of mound, size of tuber, or depth of tuber penetration. Care must be taken to avoid damage to the tuber, because damaged tubers do not store well and spoil rapidly. Some farmers use staking and mixed cropping, a practice that complicates harvesting in some cases. In forested areas, tubers grow in areas where other tree roots are present. Harvesting the tuber then involves the additional step of freeing them from other roots. This often causes tuber damage. Aerial tubers or bulbils are harvested by manual plucking from the vine. Yields may improve and cost of yam production be lower if mechanization were to be developed and adopted. However, current crop production practices and species used pose considerable hurdles to successful mechanization of yam production, particularly for small-scale rural farmers. Extensive changes in traditional cultivation practices, such as mixed cropping, may be required. Modification of current tuber harvesting equipment is necessary given yam tuber architecture and its different physical properties.


Production

In 2019, world production of yams was 74 million
tonne The tonne ( or ; symbol: t) is a metric unit of mass equal to 1,000 kilogram The kilogram (also kilogramme) is the base unit of mass Mass is the physical quantity, quantity of ''matter'' in a physical body. It is also a meas ...
s, led by
Nigeria Nigeria (), officially the Federal Republic of Nigeria, is a country in West Africa West Africa or Western Africa is the westernmost region of . The defines Western Africa as the 17 countries of , , , , , , , , , , , , , , , and as we ...

Nigeria
with 68% of the total (table).


Storage

Roots and tubers such as yam are living organisms. When stored, they continue to respire, which results in the oxidation of the
starch Starch or amylum is a polymeric A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance ...
(a polymer of glucose) contained in the cells of the tuber, which converts it into water,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, and heat energy. During this transformation of the starch, the dry matter of the tuber is reduced. Amongst the major roots and tubers, properly stored yam is considered to be the least perishable. Successful storage of yams requires: * initial selection of sound and healthy yams * proper curing, if possible combined with fungicide treatment * adequate ventilation to remove the heat generated by respiration of the tubers * regular inspection during storage and removal of rotting tubers and any sprouts that develop * protection from direct sunlight and rain Storing yam at low temperature reduces the respiration rates. However, temperatures below cause damage through chilling, causing a breakdown of internal tissues, increasing water loss and yam's susceptibility to decay. The symptoms of chilling injury are not always obvious when the tubers are still in cold storage. The injury becomes noticeable as soon as the tubers are restored to ambient temperatures. The best temperature to store yams is between , with high-technology-controlled humidity and climatic conditions, after a process of curing. Most countries that grow yams as a staple food are too poor to afford high-technology storage systems. Sprouting rapidly increases a tuber's respiration rates, and accelerates the rate at which its food value decreases. Certain cultivars of yams store better than others. The easier to store yams are those adapted to arid climate, where they tend to stay in a dormant low-respiration stage much longer than yam breeds adapted to humid tropical lands, where they do not need dormancy. Yellow yam and cush-cush yam, by nature, have much shorter dormancy periods than water yam, white yam, or lesser yam. Storage losses for yams are very high in Africa, with insects alone causing over 25% harvest loss within five months.


Nutrition

Raw yam has only moderate
nutrient densityNutrient density identifies the amount of beneficial nutrients A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definit ...
, with ''appreciable content'' (10% or more of the
Daily Value The Reference Daily Intake (RDI) used in nutrition labeling on food and dietary supplement products in the U.S. and Canada is the daily intake level of a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in ...
, DV) limited to
potassium Potassium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, b ...

potassium
,
vitamin B6 Vitamin B6 is one of the B vitamins B vitamins are a class of water-soluble vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds ...
,
manganese Manganese is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical e ...

manganese
,
thiamin Thiamine, also known as thiamin or vitamin B1, is a vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydroge ...

thiamin
,
dietary fiber Dietary fiber (British spelling fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzyme Digestive may refer to: Biology *Digestion Digestion is the breakdown of large insolub ...
, and
vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain ca ...

vitamin C
(table). But raw yam has the highest potassium levels amongst the 10 major staple foods of the world ( see nutritional chart). Yam supplies 118
calorie The calorie is a unit of energy Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a di ...
s per 100 grams. Yam generally has a lower
glycemic index The glycemic index (GI; ) is a number from 0 to 100 assigned to a food, with pure glucose arbitrarily given the value of 100, which represents the relative rise in the blood glucose level two hours after consuming that food. The GI of a specific f ...
, about 54% of
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
per 150 gram serving, compared to potato products. The protein content and quality of roots and tubers is lower than other food staples, with the content of yam and potato being around 2% on a fresh-weight basis. Yams, with
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names) is a woody shrub A shrub (often called a bush) is a small- to medium-sized perennial A perennial plant or simply perennial is a pla ...

cassava
, provide a much greater proportion of the protein intake in Africa, ranging from 5.9% in East and South Africa to about 15.9% in humid West Africa. As a relatively low-protein food, yam is not a good source of
essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms ...
s. Experts emphasize the need to supplement a yam-dominant diet with more protein-rich foods to support healthy growth in children. Yam is an important dietary element for Nigerian and West African people. It contributes more than 200 calories per person per day for more than 150 million people in West Africa, and is an important source of income. Yam is an attractive crop in poor farms with limited resources. It is rich in starch, and can be prepared in many ways. It is available all year round, unlike other, unreliable, seasonal crops. These characteristics make yam a preferred food and a culturally important food security crop in some sub-Saharan African countries.


Comparison to other staple foods

The following table shows the nutrient content of yam and major staple foods in a raw harvested form on a dry weight basis to account for their different water contents. Raw forms, however, are not edible and cannot be digested. These must be sprouted, or prepared and cooked for human consumption. In sprouted or cooked form, the relative nutritional and antinutritional contents of each of these staples is remarkably different from that of raw form of these staples.


Phytochemicals and use in medicine

The tubers of certain wild yams, including a variant of '
Kokoro is a novel by the Japanese author Natsume Sōseki , born , was a Japanese Japanese may refer to: * Something from or related to Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep re ...
' yam and other species of ''Dioscorea'', such as '' Dioscorea nipponica'', are a source for the extraction of
diosgenin Diosgenin, a phytosteroid Phytosteroids, also known as plant steroids, are naturally occurring steroid , a steroid with 27 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC The International Unio ...

diosgenin
, a
steroid A steroid is a biologically active organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

steroid
sapogenin Sapogenins are the aglycones, or non-saccharide, portions of the family of natural products known as saponins. Sapogenins contain steroid or other triterpene frameworks as their key organic feature. For example, steroidal sapogenins such as tiggeni ...
. The extracted diosgenin is used for the commercial synthesis of
cortisone Cortisone is a pregnane (21-carbon) steroid hormone. Cortisone is a naturally-occurring corticosteroid metabolite that is also used as a pharmaceutical prodrug; it is not synthesized in the adrenal glands. Cortisol is converted by the action of ...

cortisone
,
pregnenolone Pregnenolone (P5), or pregn-5-en-3β-ol-20-one, is an endogenous Endogenous substances and processes are those that originate from within a system such as an organism, Tissue (biology), tissue, or Cell (biology), cell. Endogenous substances a ...

pregnenolone
,
progesterone Progesterone (P4) is an endogenous Endogenous substances and processes are those that originate from within a system such as an organism, Tissue (biology), tissue, or Cell (biology), cell. Endogenous substances and processes contrast with exo ...

progesterone
, and other steroid products. Such preparations were used in early
combined oral contraceptive pill The combined oral contraceptive pill (COCP), often referred to as the birth control pill or colloquially as "the pill", is a type of birth control that is designed to be Oral administration, taken orally by women. It includes a combination of a ...
s. The unmodified steroid has
estrogenic Estrogen, or oestrogen, is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ...
activity.


Consumption

Yams are consumed in a variety of preparations, such as flour or whole vegetable pieces across their range of distribution in Asia, Africa, North America,
Central America Central America ( es, América Central, , ''Centroamérica'' ) is a region of the Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or ...

Central America
, the
Caribbean The Caribbean (, ; es, Caribe; french: Caraïbes; ht, Karayib; also gcf, label=Antillean Creole Antillean Creole (Antillean French Creole, Kreyol, Kwéyòl, Patois) is a French-based creole, which is primarily spoken in the Lesser Antilles ...
, South America, and
Oceania Oceania (, , ) is a geographic region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Eart ...

Oceania
.


Africa

Yams of African species must be cooked to be safely eaten, because various natural substances in yams can cause illness if consumed raw. The most common cooking methods in
Western Western may refer to: Places *Western, Nebraska, a village in the US *Western, New York, a town in the US *Western Creek, Tasmania, a locality in Australia *Western Junction, Tasmania, a locality in Australia *Western world, countries that ide ...

Western
and
Central Africa Central Africa is a subregion A subregion is a part of a larger region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhab ...

Central Africa
are by boiling, frying or roasting. Among the Akan of Ghana, boiled yam can be mashed with palm oil into ''eto'' in a similar manner to the plantain dish ''
matoke Matoke, locally also known as matooke, amatooke in Buganda (Central Uganda), ekitookye in southwestern Uganda, ekitooke in western Uganda, kamatore in Lugisu (Eastern Uganda), ebitooke in northwestern Tanzania, igitoki in Rwanda, Burundi and by ...

matoke
'', and is served with eggs. The boiled yam can also be pounded with a traditional mortar and pestle to create a thick, starchy paste known as '' iyan'' (pounded yam) which is eaten with traditional sauces such as ''
egusi Egusi (also known by variations including egwusi, agusi, ohue, agushi) is the name for the protein-rich seeds of certain cucurbitaceous plants (Squash (plant), squash, melon, gourd), which after being dried and ground are used as a major ingre ...
'' and palm nut soup. Another method of consumption is to leave the raw yam pieces to dry in the sun. When dry, the pieces turn a dark brown color. These are then milled to create a brown powder known in Nigeria as ''elubo''. The powder can be mixed with boiling water to create a thick starchy paste, a kind of pudding known as ''amala'', which is then eaten with local soups and sauces. Yams are a primary agricultural and culturally important
commodity In economics Economics () is a social science Social science is the branch A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plan ...
in
West Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 17 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, Mauritania ...

West Africa
, where over 95% of the world's yam crop is harvested. Yams are still important for survival in these regions. Some varieties of these tubers can be stored up to six months without refrigeration, which makes them a valuable resource for the yearly period of food scarcity at the beginning of the
wet season The wet season (sometimes called the rainy season) is the time of year when most of a region's average annual rainfall Rain is liquid water in the form of droplet Raindrops in a plant. A drop or droplet is a small column of liquid ...

wet season
. Yam cultivars are also cultivated in other humid tropical countries. Yam is the main staple crop of the
Igbos The Igbo people ( , also ; also spelled Ibo" and formerly also ''Iboe'', ''Ebo'', ''Eboe'', * * * ''Eboans'', ''Heebo''; natively ) are an ethnic group in Nigeria Nigeria (), officially the Federal Republic of Nigeria, is a country i ...

Igbos
in south eastern Nigeria where for centuries it played a dominant role in both their agricultural and cultural life. It is celebrated with annual yam festivals.


Brazil

Yams are particularly consumed in the coastal area of the Northeast region, although they can be found in other parts of the country. In
Pernambuco Pernambuco () is a States of Brazil, state of Brazil, located in the Northeast Region, Brazil, Northeast region of the country. With an estimated population of 9.6 million people as of 2020, it is the List of Brazilian states by population, sev ...

Pernambuco
state, it is usually boiled and served cut in slices at breakfast, along with
cheese spread Cheese spread is a soft spreadable cheese Cheese is a dairy product Dairy products or milk products are a type of food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plan ...

cheese spread
or
molasses Molasses () or black treacle Treacle () is any uncrystallised syrup In cooking Cooking or cookery is the art, science, and craft of using heat to Outline of food preparation, prepare food for consumption. Cooking techniques and ingredi ...

molasses
.


Colombia

In Colombia yam production has been specifically located in the
Caribbean region The Caribbean (, ; es, Caribe; french: Caraïbes; ht, Karayib; also gcf, label=Antillean Creole, Kawayib; nl, Caraïben; Papiamento: ) is a region of the Americas that comprises the Caribbean Sea, its surrounding coasts, and its islands (some ...
, where it has become a key product in the diet of the population of this area. In 2010, Colombia was among the 12 countries with the highest yam production worldwide, and ranked first in yield of tons per hectare planted. Although its main use is for food, several studies have shown its usefulness in the pharmaceutical industry and the manufacture of bioplastics. However, in Colombia, there is no evidence of the use of this product, other than food.


Philippines

In the Philippines, the purple ''ube'' species of yam (''
Dioscorea alata ''Dioscorea alata'', also known as purple yam, ube (), or greater yam, among many other names, is a species of yam (a tuber). The tubers are usually a vivid Violet (color), violet-purple to bright Lavender (color), lavender in color (hence the c ...

Dioscorea alata
''), is eaten as a sweetened dessert called ''
ube halaya ''Ube halaya'' or ''halayang ube'' (variant spellings ''halea'', ''haleya''; from the Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine ...

ube halaya
'', and is also used as an ingredient in another Filipino dessert, ''
halo-halo Halo-halo, also spelled ''haluhalo'', Filipino Filipino may refer to: * Something from or related to the Philippines The Philippines (; fil, Pilipinas or ''Filipinas'' ), officially the Republic of the Philippines ( fil, Republika ng P ...
''. It is also used as a popular ingredient for ice cream.


Vietnam

In Vietnam, the same purple yam is used for preparing a special type of soup ''canh khoai mỡ'' or fatty yam soup. This involves mashing the yam and cooking it until very well done. The yam root was traditionally used by peasants in Vietnam to dye cotton clothes throughout the Red River and Mekong delta regions as late as the mid-20th century, and is still used by others in the Sapa region of northern Vietnam.


Indonesia

In Indonesia, the same purple yam is used for preparing desserts. This involves mashing the yam and mixing it with coconut milk and sugar. White- and off-white-fleshed yams are cut in cubes, cooked, lightly fermented, and eaten as afternoon snacks.


Japan

An exception to the cooking rule is the mountain yam (''
Dioscorea polystachya ''Dioscorea polystachya'' or Chinese yam ( zh, s=山药, t=山藥), also called cinnamon-vine, is a species of flowering plant in the Dioscoreaceae, yam family. It is sometimes called Chinese potato or by its Japanese name ''nagaimo''. It is a pe ...

Dioscorea polystachya
''), known as ''nagaimo'' and can be further classified into ''ichōimo'' (lit. 'ginkgo-leaf yam'; kanji: 銀杏芋), or ''yamatoimo'' (lit. Yamato yam; kanji: 大和芋), depending on the root shape. Mountain yam is eaten raw and grated, after only a relatively minimal preparation: the whole tubers are briefly soaked in a vinegar-water solution to neutralize irritant oxalate crystals found in their skin. The raw vegetable is starchy and bland, mucilaginous when grated, and may be eaten plain as a side dish, or added to noodles. Another variety of yam, ''jinenjo'', is used in Japan as an ingredient in soba noodles. In Okinawa, purple yams (''
Dioscorea alata ''Dioscorea alata'', also known as purple yam, ube (), or greater yam, among many other names, is a species of yam (a tuber). The tubers are usually a vivid Violet (color), violet-purple to bright Lavender (color), lavender in color (hence the c ...

Dioscorea alata
'') are grown. This purple yam is popular as lightly deep-fried tempura, as well as being grilled or boiled. Additionally, the purple yam is a common ingredient of yam ice cream with the signature purple color. Purple yam is also used in other types of traditional ''wagashi'' sweets, cakes, and candy.


India

In central parts of India, the yam is prepared by being finely sliced, seasoned with spices, and deep fried. In Southern India, the vegetable is a popular accompaniment to rice dishes and curry. The purple yam, ''D. alata'', is also eaten in India, where it is also called the violet yam. Species may be called by the regional name "taradi", which can refer to ''Dioscorea belophylla'',Singh, K.K. and Kaushal Kumar
Ethnobotanical wisdom of Gaddi tribe in Western Himalaya
2000. p.18.
''Dioscorea deltoidea'', and ''D. bulbifera''. Digging and selling taradi is a major source of income in the region of Palampur.


Nepal

''Dioscorea ''root is traditionally eaten on ''Māgh Sankrānti'' (a midwinter festival) in Nepal. It is usually steamed and then cooked with spices.


Fiji Islands

Yam is, along with
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names) is a woody shrub A shrub (often called a bush) is a small- to medium-sized perennial A perennial plant or simply perennial is a pla ...

cassava
and
taro ''Colocasia esculenta'' is a tropical plant grown primarily for its edible corm A corm, bulbo-tuber, or bulbotuber is a short, vertical, swollen underground plant stem '' has lost its leaves, but is producing adventitious rootsImportant ...

taro
, a staple food, and is consumed boiled, roasted in a Earth oven, lovo, or steamed with fish or meat in curry sauce or coconut milk and served with rice. The cost of yam is higher due to the difficulty in farming and relatively low volume of production.


Jamaica

Because of their abundance and importance to survival, yams were highly regarded in Jamaican ceremonies and constitute part of many traditional
West Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 17 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, Mauritania ...

West Africa
n ceremonies.


The West

Yam powder is available in Western world, the West from grocers specializing in African products, and may be used in a similar manner to Instant mashed potatoes, instant mashed potato powder, although preparation is a little more difficult because of the tendency of the yam powder to form lumps. The powder is sprinkled onto a pan containing a small amount of boiling water and stirred vigorously. The resulting mixture is served with a heated sauce, such as Tomato sauce, tomato and Chili sauce, chili, poured onto it. Skinned and cut frozen yams may also be available from specialty grocers.


Toxicity

Unlike
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names) is a woody shrub A shrub (often called a bush) is a small- to medium-sized perennial A perennial plant or simply perennial is a pla ...

cassava
, most varieties of edible, mature, cultivated yam do not contain toxic compounds. However, there are exceptions. Bitter compounds tend to accumulate in immature tuber tissues of white and yellow yams. These may be polyphenols or tannin-like compounds. Wild forms of bitter yams (''Dioscorea dumetorum'') do contain some toxins, such as dihydrodioscorine, that taste bitter, hence are referred to as bitter yam. Bitter yams are not normally eaten except at times of desperation in poor countries and in times of local food scarcity. They are usually detoxified by soaking in a vessel of salt water, in cold or hot fresh water or in a stream. The bitter compounds in these yams are water-soluble alkaloids which, on ingestion, produce severe and distressing symptoms. Severe cases of alkaloid intoxication may prove fatal. Aerial or potato yams (''D. bulbifera'') have antinutritional factors. In Asia, detoxification methods, involving water extraction, fermentation, and roasting of the grated tuber, are used for bitter cultivars of this yam. The bitter compounds in yams also known locally as air potato include diosbulbin and possibly saponins, such as
diosgenin Diosgenin, a phytosteroid Phytosteroids, also known as plant steroids, are naturally occurring steroid , a steroid with 27 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC The International Unio ...

diosgenin
. In Indonesia, an extract of air potato is used in the preparation of arrow poison.


Cultural aspects

Historical records in West Africa and of African yams in Europe date back to the 16th century. Yams were taken to the Americas through precolonial Portuguese and Spanish on the borders of Brazil and Guyana, followed by a dispersion through the Caribbean. Yams are used in Papua New Guinea, where they are called ''kaukau''. Their cultivation and harvesting is accompanied by complex rituals and taboos. The coming of the yams (one of the numerous versions from Maré) is described in Pene Nengone (Loyalty Islands of New Caledonia).


Nigeria and Ghana

A yam festival is usually held in the beginning of August at the end of the rainy season. People offer yams to gods and ancestors first, before distributing them to the villagers. This is their way of giving thanks to the spirits above them. The New Yam Festival celebrates the main agricultural crop of the
Igbos The Igbo people ( , also ; also spelled Ibo" and formerly also ''Iboe'', ''Ebo'', ''Eboe'', * * * ''Eboans'', ''Heebo''; natively ) are an ethnic group in Nigeria Nigeria (), officially the Federal Republic of Nigeria, is a country i ...

Igbos
, Idomas, and Tivs. The New Yam Festival, known as ''Orureshi'' in Owukpa in Idoma west and ''Ima-Ji'', ''Iri-Ji'' or ''Iwa Ji'' in Igbo land, is a celebration depicting the prominence of yam in social and cultural life. The festival is prominent among southeastern states and major tribes in Benue State, mainly around August. The Igbo people accord special respect to yam to the extent that no one eats the newly harvested yam until the New Yam celebrations / feast is marked. It is called Iri ji ọhụrụ. People return to their various communities for the celebrations.


References


External links

* {{DEFAULTSORT:Yam (vegetable) Yams (vegetable), Crops originating from Africa Dioscorea Flora of Jamaica Igbo cuisine Root vegetables Staple foods Tropical agriculture Tubers Yoruba cuisine Crops Plant dyes