Taiwanese and Sweet Potato
In Taiwan, sweet potato (Ipomoea batatas) is very popular. You can see it as all different varieties of dessert, staple food, and greens. Baked sweet potatoes are also very popular during winter. People in Taiwan also call themselves as “sweet potatoes”. The interesting thing is, this crop is not originated from Taiwan. It does not even have an Asian heritage — it comes all the way from the Americas.
The sweet potato is a dicotyledonous plant that belongs to the morning glory family, Convolvulaceae. It is mostly used as a root vegetable, but the young leaves and shoots can be eaten as greens and is quite popular in Taiwan. When you order a plate of quick-boiled vegetables (燙青菜) from any restaurant, leaves of sweet potato is usually one of the popular choice.
Although it is called “sweet potato”, it is only distantly related to the potato (Solanum tuberosum) and does not belong to the nightshade family, Solanaceae.
The plant is a herbaceous perennial vine, bearing alternate heart-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered, with a smooth skin with color of yellow, orange, red, brown, purple, or beige. Its flesh ranges from beige through white, red, pink, violet, yellow, orange, and purple.
Ipomoea batatas is native to the tropical regions in the Americas. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance in the world. Another species of Ipomoea in Taiwan, I. aquatica (“kangkung”/空心菜/甕菜 in Southeastern Asia and Taiwan), is also very important as greens. Aside from sweet potato and I. aquatica, many species of Convolvulaceae are poisonous.
In Argentina, Venezuela, Puerto Rico and the Dominican Republic the sweet potato is called batata, which is included in its binomial name. The word “batata” is originated from Taino (indigenous people in the Caribbean) which is the name for sweet potato there.
The origin and domestication of sweet potato is thought to be in either Central or South America. In Central America, sweet potatoes were domesticated at least 5,000 years ago. It is postulated that the origin of I. batatas was between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. The cultigen had most likely been spread by local people to the Caribbean and South America by 2500 BC. Sweet potatoes are cultivated throughout tropical and warm temperate regions wherever there is sufficient water to support their growth.
After Christopher Columbus (1451–1506) discovered the Americas, the Europeans encountered it in the province of Dari’an, Panama, and it was Columbus who introduces it to Isabella I of Castile in 1493, and introduces to Island of Hispaniola (now Haiti/Dominican Republic) in 1508.
The Spaniards found that sweet potatoes are quite adaptable to the Spanish climate and that the sweet taste has made sweet potatoes popular in Europe.
At that time, in addition to being a delicacy on the table of wealthy people, the sweet potato in Europe was also rumored that the it could have medicinal effects. At the time, Europeans believed that sweet potatoes could speed up menstrual periods and the production of milk for women, while it has aphrodisiac effects on men.
The Henry VIII of England is convinced of the aphrodisiac effect of sweet potatoes, and particularly likes the sweet potato pie with spices and sugar.
Sweet Potato in Taiwan
The sweet potato may have been introduced into Fujian via the Philippines (which was then a Spanish colony). In the 1580s, Chen Zhenlong (陳振龍，?-1619) of Changle, Fujian brought sweet potatoes back from Luzon Island (probably smuggled because the Spaniards banned export of sweet potatoes).
The growing of sweet potatoes was encouraged by the Governor Chin Hsüeh-tseng (Jin Xuezeng 金學曾，?-?). After its introduction to China, it was mainly spread in Fujian and Guangdong during the first hundred years. After sweet potato saved Chinese people from a major crop failure, it began to spread to Jiangxi, Hunan, and Zhejiang in the 17th century. In the middle of the 18th century, it also spread to the Yellow River Basin and further north. However, when the sweet potato is in the north, it is necessary to dig up the roots and keep it in the cellar during the winter for storage.
Those who are primarily devoted to the dissemination of sweet potatoes include Xu Guangqi, Chen Zhenlong and his son Chen Jinglun(陳經綸，?-?).
As a high-yielding hardy crop and suitable for cultivation in south of the Nanling Mountains area almost every year, the “Relief Book for Saving the Famine” (救荒簡易書) written at the end of the nineteenth century stated that sweet potatoes can be planted from January to August and can be harvested up from the summer solstice to the beginning of the winter.
In the early years of the reign of Emperor Qianlong(乾隆，1711–1799，reigned 1735–1796), there was a continuous drought in Northern part of China. Fang Guancheng(方觀承，1696–1768) wrote an article (賑紀) to stress the importance of introducing sweet potatoes. Later, Qianlong asked all provinces to plant sweet potatoes.
As a big fan for sweet potatoes, Xu Guangqi (徐光啟，1562–1633) listed 13 advantages of sweet potatoes in his “Agricultural Administration Book” (農政全書): high-yielding, as nutritious as yam, very easy growing, resistant to wind, can be used as staple food, capable of wine-brewing, suitable for storage,can be eaten raw or cooked, don’t need much land nor water.
It is not clear when sweet potato is introduced to Taiwan. The first record of sweet potato cultivation in Taiwan was written by Chen Di (陳第，1541–1617) in his book Dōng Fān Jì (東番記, account of an expedition to Taiwan) written in 1603, suggesting that sweet potatoes is growing in Taiwan before that time. However, sweet potatoes was not used as staple food around that time; it was classified as vegetables.
Sweet potatoes gradually become staple food for aboriginal people. People from Bunun tribe (布農) even include the time for plant sweet potatoes (April) and Sweet Potato Festival (moraniyan/masuadhutan, November/December) in their calendar.
During the Dutch colonial era, the Dutch did not have much interest in sweet potatoes, they mainly encouraged indigenous people to grow rice and sugarcane. Ironically, it was sweet potatoes helped Koxinga (鄭成功, 1624–1662) to defeat them. Koxinga and his army besiege the Fort Zeelandia for nine months by growing sweet potatoes. There is a legend saying that he invented oyster omelette (蚵仔煎), a dish of oyster and sweet potato starch. Prince of Lu (Zhu Yihai, 朱以海, 1618–1662) of Ming Dynasty was remembered as Sweet Potato Prince.
Storing sweet potatoes at room temperature in (sub-)tropical climate is not a good idea because they sprout readily. It is probably the people in Taiwan invented a way for long-term storage: they grate sweet potatoes and sun-dried them. In this way, dried grated sweet potatoes (番薯簽) can be stored for at least a year.
Dried grated sweet potatoes accompanied Taiwanese people throughout the Qing dynasty, Japanese occupation period and the early stage of Chinese Nationalist one-party rule.
Just before WWII, Japanese people discovered that the sweet potato starch can be fermented to producing ethanol, methanol, butanol and acetone. The plant for producing these organic solvent, which was located in Chiayi, was destroyed by US Army Air Force during WWII [ref]. In addition to produce organic solvent, sweet potatoes also become a substitute for staple food at that time.
After WWII, because Taiwan did not have a fertilizer industry at the time, rice was continuously exported to Japan in large quantities to sell for meeting the demand of fertilizer. Therefore, Taiwanese people were still eating sweet potatoes.
The most prosperous period of sweet potato cultivation in Taiwan was between 1950 and 1970, when the cultivated area was 200,000 to 400,000 hectares and the annual output was between 200 to 340 million metric tons.
At that time, it was mainly used as feed for livestock and staple food supplements. The Agriculture and Food Agency promoted “millets*, pig raising, and rice farming.” Using sweet potatoes produced in winter to feed pigs, pig excrement can be used as compost to increase rice production.
Sweet potatoes gradually faded from the table. The proportion of sweet potatoes as staple food dropped from 40% in 1945 to 25% in 1950–1960 and then dropped to 19% in 1965, while livestock feed use increased from 35% to 50%.
Later, it was replaced by imported corn in livestock feed use, and the planting area of sweet potatoes fell. The consumption of sweet potatoes as staple food and leafy vegetables increased in recent years as a healthy diet trend and sweet potatoes became second only to rice.
Breeding of Sweet Potatoes
Since 1907, the Agricultural Experiment Branch began to import sweet potato varieties around the world to Taiwan. From 1914 to 1918, 11 suitable varieties were selected from over 170 varieties. Crossbreeding began in 1922 and was chaired by Horomichiro Hirama (平間梗三郎) from the Chiayi Agricultural Experiment Branch.
Until 1944, the Chiayi branch bred and selected 33 fine varieties, all named after the “Tainong No. XX.” Their work continued by the new government after WWII.
Tainong №57 was bred and selected in 1955 by crossbreeding Tainong №27 with Nancy hall. Yellow skin and yellow flesh, it is suitable for baking, boiling and frying and are most cultivated varieties.
Tainong №66 was bred and selected in 1975. It has orange flesh and nicknamed as “red-hearted sweet potatoes.”.
Tainong №64 was popular in Zhushan, Nantou. There is a saying in Taiwan stated that “Sweet potatoes from Zhushan is the best.”
Tainong №73 has purple flesh due to overproduction of anthocyanin. It was bred and selected in 2002 and nickname as “taro sweet potato”.
The latest addition is Tainong No74, which was bred and selected in 2017. It has yellow flesh and brownish-red skin and can be stored under room temperature for over 28 days without sprouting. The latter characteristic is especially important for exporting to Europe and Americas.
There are also two varieties for leafy vegetables: Tainong №71 and Taoyuan №2.
Why Taiwanese call themselves “Sweet Potatoes”?
If you look at the map of Taiwan, you’ll probably agree with me: the shape of the island is a reminiscence of the root of sweet potato. The first one to propose this in the official literature that the island of Taiwan is shaped like a sweet potato is probably Professor Yasumoto Yamamoto (山本由松) of Taipei Imperial University (now National Taiwan University). In addition to describing the shape of Taiwan with sweet potatoes, he also uses eucalyptus leaves. In addition, news reports in Japan also said: “The shape of Taiwan is like a sweet potato.”
According to oral history of the Taiwanese in the Japanese occupation era collected by history scholar Xu Xueji (許雪姬) , it is probably start with the Japanese occupation era. At the time, Taiwanese traveled to areas of China that was controlled by Japan to work faced a difficult situation: on the one hand, they were regarded as pro-China by the Japanese; on the other hand, they were regarded as pro-Japanese by the Chinese. Therefore, they often refused to say that they came from Taiwan and all of them just use the nickname “sweet potatoes” to identify themselves.
It may also be because the people from other provinces came to Taiwan and saw that Taiwanese people mostly eat sweet potatoes as their staple food. They then nicknamed the Taiwanese people as “sweet potatoes” and said that eating sweet potatoes was making them dumb; and Taiwanese People then called these people from other provinces as “taros”.
Another story has it as: When the people from other provinces first arrived in Taiwan, they couldn’t distinguish between the sweet potato and the taro, and they often end up buying taros when they want to buy sweet potatoes. Therefore, people from the other provinces were nicknamed as taro.
Is sweet potato a natural GMO?
A study published in 2015 found that the genome of cultivated sweet potatoes contains two stretches of DNA sequences from Agrobacterium, with genes being actively expressed by the plants. Transgenes were observed both in the closely related wild relatives and in more distantly related wild species. The first stretch of DNA, which is present among all cultivars, containing genes for auxin production, which probably make sweet potatoes grow faster; the second stretch of DNA has no observable effect and is much less prevalent. This observation makes cultivated sweet potatoes the first known example of a naturally transgenic food crop.
As a staple crop in Taiwan in the old times, older generation Taiwanese has mixed feelings toward sweet potatoes. Some hate it because it brings back the old memories of hardship. Most of the younger generations get acquainted to sweet potatoes from extracurricular activities — they make “stove” with rocks and clods and roast sweet potatoes within it. For them, sweet potatoes probably bring back happy memories. I still remember the first time sweet potato greens become popular, my mom mumbled “in my times sweet potato greens are for pigs”. As time goes by, memories fade and crops are reassigned new meanings.
*the “millets” here is referring to cereals excluding wheat, barley, maize and soybean.
Literature Cited
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彭世獎著。2012。中國作物栽培簡史。中國農業出版社。ISBN 9787109169258
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Tina Kyndt, Dora Quispe, Hong Zhai, Robert Jarret, Marc Ghislain, Qingchang Liu, Godelieve Gheysen, and Jan F. Kreuze. 2015. The genome of cultivated sweet potato contains Agrobacterium T-DNAs with expressed genes: An example of a naturally transgenic food crop. PNAS. published ahead of print, doi:10.1073/pnas.1419685112
