Yams at a refugee camp in Chad
Yams and sweet potatoes are important food sources in the Third World, especially in Oceania, Southeast Asia, the Caribbean, parts of South America and West Africa. Both are root crops but from different families that in turn are different from the family that includes regular potatoes. The scientific name of the sweet potato is “Ipomoea batatas” . The yam is one of several species of “Dioscorea” .

Sweet potatoes come from creeping perennial vines that are members of the morning glory family. Technically they are true roots not underground stems (tubers) as is the case with white potatoes and yams. A single sweet potato planted in the spring produces a large vine with a large number of tubers growing from its roots. Sweet potato plants are obtained by planting slips — not seeds — in indoor or outdoor beds and transplanting these a month or so later.

Sweet potatoes are one of the most valuable crops in the world, sustaining human communities for centuries and providing more nutrients per farmed acre than any other staple. Sweet potatoes yield more food per acre than any other plant and exceed potatoes and many grains as sources of proteins, sugars, fats and many vitamins. The leaves of some varieties of sweet potatoes are eaten like spinach.

Sweet potatoes originated from in southern Mexico where its wild ancestors are still found today, and were first cultivated there . Sweet potato agriculture spread throughout the Americas and to the islands of the Caribbean. Columbus is credited with bringing the first sweet potatoes from the New World to Europe. In the 16th century the plants spread throughout Africa and were introduced to Asia. An effort is being made to encourage people to eat yellow sweet potato which is high in Vitamin A as opposed to white sweet potato which lacks the nutrient.

Modified and genetically-engineered sweet potatoes hold great promise for poor farmers. Scientists have recently introduced high-yield and protein rich sweet potato varieties that have gone a long way towards reducing hunger in the parts of the world where these plants are raised. Scientists in Kenya have developed a sweet potato that wards off viruses. Monsanto has developed disease-resistant sweet potatoes that are widely used in Africa.

Tubers and Root Crops

There is some confusion as to whether potatoes, cassava, sweet potatoes and yams are tubers or roots. Contrary to what many people think tubers are not roots. They are underground stems that serve as food storage units for the green foliage above the ground. Roots absorb nutrients, tubers store them.

A tuber is the thick underground part of a stem or rhizome that stores food and bears buds from which new plants arise. They are generally storage organs used to store nutrients for survival in of the winter or dry months and to provide energy and nutrients for regrowth during the next growing season through asexual reproduction. [Source: Wikipedia]

Stem tubers form thickened rhizomes (underground stems) or stolons (horizontal connections between organisms). Potatoes and yams are stem tubers. The term “root tuber” is used by some to describe modified lateral roots such as sweet potatoes, cassava, and dahlias. Typically they are described as root crops.

Fred Benu of the Universitas Nusa Cendana wrote: Root crops have modified roots to function as storage organs, while tuber crops have modified stems or roots to function as both storage and propagation organs. As such, the modified roots of root crops cannot propagate new crops, whereas the modified stem or roots of tuber crops can propagate new crops. Examples of root crops are potato, sweet potato, and dahlia; examples of tuber crops are carrot, sugar beet, and parsnip.

Sweet Potato Colonized the World By Themselves?

The sweet potato originated in the Americas and spread across the globe by themselves. It was originally thought that they potatoes were carried to the islands of the Pacific where they are popular today from the Americas by humans centuries before the arrival of Columbus. Since it seem unlikely the seeds floated across the Pacific it is believed that pre-Columbian men in boats, either from the Americas or the Pacific, carried them there. This turns out not to be the case according to a study published in 2018.

Carl Zimmer wrote in the New York Times:“Of all the plants that humanity has turned into crops, none is more puzzling than the sweet potato. Indigenous people of Central and South America grew it on farms for generations, and Europeans discovered it when Christopher Columbus arrived in the Caribbean. In the 18th century, however, Captain Cook stumbled across sweet potatoes again — over 4,000 miles away, on remote Polynesian islands. European explorers later found them elsewhere in the Pacific, from Hawaii to New Guinea. The distribution of the plant baffled scientists. How could sweet potatoes arise from a wild ancestor and then wind up scattered across such a wide range? Was it possible that unknown explorers carried it from South America to countless Pacific islands? [Source: Carl Zimmer, New York Times, April 12, 2018]

An extensive analysis of sweet potato DNA, published in Current Biology, comes to a controversial conclusion: Humans had nothing to do with it. The bulky sweet potato spread across the globe long before humans could have played a part — it’s a natural traveler. Some agricultural experts are skeptical. “This paper does not settle the matter,” said Logan J. Kistler, the curator of archaeogenomics and archaeobotany at the Smithsonian Institution. Alternative explanations remain on the table, because the new study didn’t provide enough evidence for exactly where sweet potatoes were first domesticated and when they arrived in the Pacific. “We still don’t have a smoking gun,” Dr. Kistler said.

History of Sweet Potatoes

Research indicates that only one wild plant is the ancestor of all sweet potatoes. Carl Zimmer wrote in the New York Times: The closest wild relative is a weedy flower called Ipomoea trifida that grows around the Caribbean. Its pale purple flowers look a lot like those of the sweet potato. Instead of a massive, tasty tuber, I. trifida grows only a pencil-thick root. “It’s nothing we could eat,” one scientist said. [Source: Carl Zimmer, New York Times, April 12, 2018]

The ancestors of sweet potatoes split from I. trifida at least 800,000 years ago, the scientists calculated. To investigate how they arrived in the Pacific, the team headed to the Natural History Museum in London.The leaves of sweet potatoes that Captain Cook’s crew collected in Polynesia are stored in the museum’s cabinets. The researchers cut bits of the leaves and extracted DNA from them. The Polynesian sweet potatoes turned out to be genetically unusual — “very different from anything else,” Mr. Muñoz-Rodríguez said.

The sweet potatoes found in Polynesia split off over 111,000 years ago from all other sweet potatoes the researchers studied. Yet humans arrived in New Guinea about 50,000 years ago, and only reached remote Pacific islands in the past few thousand years.The age of Pacific sweet potatoes made it unlikely that any humans, Spanish or Pacific Islander, carried the species from the Americas, Mr. Muñoz-Rodríguez said.

Traditionally, researchers have been skeptical that a plant like a sweet potato could travel across thousands of miles of ocean. But in recent years, scientists have turned up signs that many plants have made the voyage, floating on the water or carried in bits by birds.Even before the sweet potato made the journey, its wild relatives traveled the Pacific, the scientists found. One species, the Hawaiian moonflower, lives only in the dry forests of Hawaii — but its closest relatives all live in Mexico. The scientists estimate that the Hawaiian moonflower separated from its relatives — and made its journey across the Pacific — over a million years ago.

Debate About Sweet Potato Origins

Carl Zimmer wrote in the New York Times: Scientists have offered a number of theories to explain the wide distribution of I. batatas. Some scholars proposed that all sweet potatoes originated in the Americas, and that after Columbus’s voyage, they were spread by Europeans to colonies such as the Philippines. Pacific Islanders acquired the crops from there.As it turned out, though, Pacific Islanders had been growing the crop for generations by the time Europeans showed up. On one Polynesian island, archaeologists have found sweet potato remains dating back over 700 years. [Source: Carl Zimmer, New York Times, April 12, 2018]

A radically different hypothesis emerged: Pacific Islanders, masters of open-ocean navigation, picked up sweet potatoes by voyaging to the Americas, long before Columbus’s arrival there. The evidence included a suggestive coincidence: In Peru, some indigenous people call the sweet potato cumara. In New Zealand, it’s kumara. A potential link between South America and the Pacific was the inspiration for Thor Heyerdahl’s famous 1947 voyage aboard the Kon-Tiki. He built a raft, which he then successfully sailed from Peru to the Easter Islands.

Genetic evidence only complicated the picture. Examining the plant’s DNA, some researchers concluded that sweet potatoes arose only once from a wild ancestor, while other studies indicated that it happened at two different points in history. According to the latter studies, South Americans domesticated sweet potatoes, which were then acquired by Polynesians. Central Americans domesticated a second variety that later was picked up by Europeans.

Hoping to shed light on the mystery, a team of researchers recently undertook a new study — the biggest survey of sweet potato DNA yet. And they came to a very different conclusion. “We find very clear evidence that sweet potatoes could arrive in the Pacific by natural means,” said Pablo Muñoz-Rodríguez, a botanist at the University of Oxford. He believes the wild plants traveled thousands of miles across the Pacific without any help from humans. Mr. Muñoz-Rodríguez and his colleagues visited museums and herbariums around the world to take samples of sweet potato varieties and wild relatives. The researchers used powerful DNA-sequencing technology to gather more genetic material from the plants than possible in earlier studies.

But Tim P. Denham, an archaeologist at the Australian National University who was not involved in the study, found this scenario hard to swallow. It would suggest that the wild ancestors of sweet potatoes spread across the Pacific and were then domesticated many times over — yet wound up looking the same every time. “This would seem unlikely,” he said.

Dr. Kistler argued that it was still possible that Pacific Islanders voyaged to South America and returned with the sweet potato. A thousand years ago, they might have encountered many sweet potato varieties on the continent. When Europeans arrived in the 1500s, they likely wiped out much of the crop’s genetic diversity. As a result, Dr. Kistler said, the surviving sweet potatoes of the Pacific only seem distantly related to the ones in the Americas. If the scientists had done the same study in 1500, Pacific sweet potatoes would have fit right in with other South American varieties.

World’s Top Sweet Potato Producing Countries

World’s Top Producers of Sweet Potatoes (2020): 1) China: 48949495 tonnes; 2) Malawi: 6918420 tonnes; 3) Tanzania: 4435063 tonnes; 4) Nigeria: 3867871 tonnes; 5) Angola: 1728332 tonnes; 6) Ethiopia: 1598838 tonnes; 7) United States: 1558005 tonnes; 8) Uganda: 1536095 tonnes; 9) Indonesia: 1487000 tonnes; 10) Vietnam: 1372838 tonnes; 11) Rwanda: 1275614 tonnes; 12) India: 1186000 tonnes; 13) Madagascar: 1130602 tonnes; 14) Burundi: 950151 tonnes; 15) Brazil: 847896 tonnes; 16) Japan: 687600 tonnes; 17) Papua New Guinea: 686843 tonnes; 18) Kenya: 685687 tonnes; 19) Mali: 573184 tonnes; 20) North Korea: 556246 tonnes

World’s Top Producers (in terms of value) of Sweet Potatoes (2019): 1) China: Int.$10704579,000 ; 2) Malawi: Int.$1221248,000 ; 3) Nigeria: Int.$856774,000 ; 4) Tanzania: Int.$810500,000 ; 5) Uganda: Int.$402911,000 ; 6) Indonesia: Int.$373328,000 ; 7) Ethiopia: Int.$362894,000 ; 8) Angola: Int.$347246,000 ; 9) United States: Int.$299732,000 ; 10) Vietnam: Int.$289833,000 ; 11) Rwanda: Int.$257846,000 ; 12) India: Int.$238918,000 ; 13) Madagascar: Int.$230060,000 ; 14) Burundi: Int.$211525,000 ; 15) Kenya: Int.$184698,000 ; 16) Brazil: Int.$166460,000 ; 17) Japan: Int.$154739,000 ; 18) Papua New Guinea: Int.$153712,000 ; 19) North Korea: Int.$116110,000 ; [An international dollar (Int.$) buys a comparable amount of goods in the cited country that a U.S. dollar would buy in the United States.]

Top Sweet-Potato-Producing Countries in 2008: (Production, $1000; Production, metric tons, FAO): 1) China, 4415253 , 80522926; 2) Nigeria, 333425 , 3318000; 3) Uganda, 272026 , 2707000; 4) Indonesia, 167919 , 1876944; 5) United Republic of Tanzania, 132847 , 1322000; 6) Viet Nam, 119734 , 1323900; 7) India, 109936 , 1094000; 8) Japan, 99352 , 1011000; 9) Kenya, 89916 , 894781; 10) Mozambique, 89436 , 890000; 11) Burundi, 87794 , 873663; 12) Rwanda, 83004 , 826000; 13) Angola, 82378 , 819772; 14) United States of America, 75222 , 836560; 15) Madagascar, 62605 , 890000; 16) Papua New Guinea, 58284 , 580000; 17) Philippines, 54668 , 572655; 18) Ethiopia, 52906 , 526487; 19) Argentina, 34166 , 340000; 20) Cuba, 33915 , 375000;


20120525-New Guinea Yams.jpg
New Guinea yams
Yams are tubers. Over 500 species of yam have been identified world wide. Wild yams can be found in a lot of places. They are often clinging vines that grow on trees. In temperate climates they are perennials whose leaves die off in the winter and who store their energy in their tuber or rhizome and use that to fuel growth the following spring.

Yams are full of nutrients and can grow to a very large size. Yams grow best in tropical regions but will grow anywhere there is four months without a frost or strong winds. They grow best in well drained, loose, sandy loam. They are very popular in the Pacific and a key crop in African agriculture.

Yams were originally thought to have originated in southeast Asia and somehow were introduced to Africa centuries before explorers traveled between the two regions. The technique of dating starch granules found in cracks in rocks used to grind up plant material have has been used to find the earliest known use of several foods, including yams from China dated to between 19,500 and 23,000 years ago. [Source: Ian Johnston, The Independent, July 3, 2017]

Buy genetic analysis, according to a paper published in Science Magazine. indicates yams were first domesticated in the Niger River basin of West Africa Archaeology magazine reported: A team led by France's Institute for Research and Development plant geneticist Nora Scarcelli sequenced 167 genomes of wild and domesticated yams collected from West African countries such as Ghana, Benin, Nigeria, and Cameroon. They found that yams were domesticated from the forest species D. praehensilis. Researchers had believed yams may have been domesticated from a different species that thrives in Africa's tropical savanna. Previous genetic studies have shown that African rice and the grain pearl millet were also domesticated in the Niger River basin. The finding that yams were first farmed there supports the theory that the region was an important cradle of African agriculture, much like the Fertile Crescent in the Near East.[Source: Archaeology magazine, May 3, 2019]

World’s Top Yam Producing Countries

World’s Top Producers of Yams (2020): 1) Nigeria: 50052977 tonnes; 2) Ghana: 8532731 tonnes; 3) Côte d'Ivoire: 7654617 tonnes; 4) Benin: 3150248 tonnes; 5) Togo: 868677 tonnes; 6) Cameroon: 707576 tonnes; 7) Central African Republic: 491960 tonnes; 8) Chad: 458054 tonnes; 9) Colombia: 423827 tonnes; 10) Papua New Guinea: 364387 tonnes; 11) Guinea: 268875 tonnes; 12) Brazil: 250268 tonnes; 13) Gabon: 217549 tonnes; 14) Japan: 174012 tonnes; 15) Sudan: 166843 tonnes; 16) Jamaica: 165169 tonnes; 17) Mali: 109823 tonnes; 18) Democratic Republic of the Congo: 108548 tonnes; 19) Senegal: 95347 tonnes; 20) Haiti: 63358 tonnes [Source: FAOSTAT, Food and Agriculture Organization (U.N.), fao.org. A tonne (or metric ton) is a metric unit of mass equivalent to 1,000 kilograms (kgs) or 2,204.6 pounds (lbs). A ton is an imperial unit of mass equivalent to 1,016.047 kg or 2,240 lbs.]

World’s Top Producers (in terms of value) of Yams (2019): 1) Nigeria: Int.$13243583,000 ; 2) Ghana: Int.$2192985,000 ; 3) Côte d'Ivoire: Int.$1898909,000 ; 4) Benin: Int.$817190,000 ; 5) Togo: Int.$231323,000 ; 6) Cameroon: Int.$181358,000 ; 7) Chad: Int.$149422,000 ; 8) Central African Republic: Int.$135291,000 ; 9) Colombia: Int.$108262,000 ; 10) Papua New Guinea: Int.$100046,000 ; 11) Brazil: Int.$66021,000 ; 12) Haiti: Int.$65181,000 ; 13) Gabon: Int.$61066,000 ; 14) Guinea: Int.$51812,000 ; 15) Sudan: Int.$50946,000 ; 16) Jamaica: Int.$43670,000 ; 17) Japan: Int.$41897,000 ; 18) Democratic Republic of the Congo: Int.$29679,000 ; 19) Cuba: Int.$22494,000 ; [An international dollar (Int.$) buys a comparable amount of goods in the cited country that a U.S. dollar would buy in the United States.]

Top Yam-Producing Countries in 2008 (Production, $1000; Production, metric tons, FAO): 1) Nigeria, 5652864 , 35017000; 2) Côte d'Ivoire, 1063239 , 6932950; 3) Ghana, 987731 , 4894850; 4) Benin, 203525 , 1802944; 5) Togo, 116140 , 638087; 6) Chad, 77638 , 405000; 7) Central African Republic, 67196 , 370000; 8) Papua New Guinea, 62554 , 310000; 9) Cameroon, 56501 , 350000; 10) Haiti, 47420 , 235000; 11) Colombia, 46654 , 265752; 12) Ethiopia, 41451 , 228243; 13) Japan, 33121 , 181200; 14) Brazil, 32785 , 250000; 15) Sudan, 27645 , 137000; 16) Gabon, 23407 , 158000; 17) Jamaica, 20639 , 102284; 18) Cuba, 19129 , 241800; 19) Mali, 18161 , 90000; 20) Democratic Republic of the Congo, 17412 , 88050;


20120525-Potatoes Patates.jpg
Even though they are 80 percent water potatoes are one of the most nutritiously complete foods. They are packed with protein, carbohydrates and numerous vitamins and minerals — including potassium and vitamin C and important trace minerals — and are 99.9 percent fat-free The are so nutritious it is possible to live solely on potatoes and one protein-rich food such as milk. Charles Crissman of the International Potato Center in Lima told the Times of London, “On mashed potatos alone, you would be doing pretty good.”

Potatoes belong to the “Solanum” , genus of plants, which also includes the tomato, pepper, eggplant, petunia, tobacco plants and deadly nightshade and more than other 2,000 species, of which about 160 are tubers. [Source: Robert Rhoades, National Geographic, May 1992 ╺; Meredith Sayles Hughes, Smithsonian]

Potatoes are regarded as the world’s forth most important food after corn, wheat and rice. The United Nations declared 2008 to be the International Year of the Potato. Potatoes are an ideal crop. They produce a lot of food; don’t take long to grow; do well in poor soils; tolerate bad weather and don’t require much skill to raise. An acre of these tubers yields twice as much food as an acre of grain and matures in 90 to 120 days. One nutritionist told the Los Angeles Times that potatoes are “a great way of turning the ground into a calorie machine.”


Taro is a starchy tuber that come from a huge-leafed plant that is cultivated in freshwater swamps. The leaves are so large they are sometimes used as umbrellas. Harvester often immerse themselves waist deep in muck to collect it. After breaking off the bulbous rootstock, the top is replanted. Taro is popular in Africa and the Pacific.

World’s Top Producers of Taro (Cocoyam) (2020): 1) Nigeria: 3205317 tonnes; 2) Ethiopia: 2327972 tonnes; 3) China: 1886585 tonnes; 4) Cameroon: 1815246 tonnes; 5) Ghana: 1251998 tonnes; 6) Papua New Guinea: 281686 tonnes; 7) Burundi: 243251 tonnes; 8) Madagascar: 227304 tonnes; 9) Rwanda: 188042 tonnes; 10) Central African Republic: 133507 tonnes; 11) Japan: 133408 tonnes; 12) Laos: 125093 tonnes; 13) Egypt: 119425 tonnes; 14) Guinea: 117529 tonnes; 15) Philippines: 107422 tonnes; 16) Thailand: 99617 tonnes; 17) Côte d'Ivoire: 89163 tonnes; 18) Gabon: 86659 tonnes; 19) Democratic Republic of the Congo: 69512 tonnes; 20) Fiji: 53894 tonnes [Source: FAOSTAT, Food and Agriculture Organization (U.N.), fao.org]

World’s Top Producers (in terms of value) of Taro (Cocoyam) (2019): 1) Nigeria: Int.$1027033,000 ; 2) Cameroon: Int.$685574,000 ; 3) China: Int.$685248,000 ; 4) Ghana: Int.$545101,000 ; 5) Papua New Guinea: Int.$97638,000 ; 6) Madagascar: Int.$81289,000 ; 7) Burundi: Int.$78084,000 ; 8) Rwanda: Int.$61675,000 ; 9) Laos: Int.$55515,000 ; 10) Central African Republic: Int.$50602,000 ; 11) Japan: Int.$49802,000 ; 12) Egypt: Int.$43895,000 ; 13) Guinea: Int.$39504,000 ; 14) Thailand: Int.$38767,000 ; 15) Philippines: Int.$37673,000 ; 16) Gabon: Int.$34023,000 ; 17) Côte d'Ivoire: Int.$29096,000 ; 18) Democratic Republic of the Congo: Int.$24818,000 ; 19) Fiji: Int.$18491,000 ; [An international dollar (Int.$) buys a comparable amount of goods in the cited country that a U.S. dollar would buy in the United States.]

Image Sources: Wikimedia Commons

Text Sources: National Geographic, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2022

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