Sweet potato
The sweet potato or sweetpotato is a dicotyledonous plant in the morning glory family, Convolvulaceae. Its sizeable, starchy, sweet-tasting tuberous roots are used as a root vegetable, which is a staple food in parts of the world. Cultivars of the sweet potato have been bred to bear tubers with flesh and skin of various colors. Moreover, the young shoots and leaves are occasionally eaten as greens. The sweet potato and the potato are only distantly related, both being in the order Solanales. Although darker sweet potatoes are often known as yams in parts of North America, they are even more distant from actual yams, which are monocots in the order Dioscoreales.
The sweet potato is native to the tropical regions of South America in present-day Ecuador. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance—some others are used locally, but many are poisonous. The genus Ipomoea that contains the sweet potato also includes several garden flowers called morning glories, but that term is not usually extended to I. batatas. Some cultivars of I. batatas are grown as ornamental plants under the name tuberous morning glory and used in a horticultural context. Sweet potatoes can also be called yams in North America.
Description
The plant is a herbaceous perennial vine, bearing alternate triangle-shaped or palmately lobed leaves and medium-sized sympetalous flowers. The stems are usually crawling on the ground and form adventitious roots at the nodes. The leaves are screwed along the stems. The leaf stalk is long. The leaf blades are very variable, long, the shape is heart-, kidney- to egg-shaped, rounded or triangular and spear-shaped, the edge can be entire, toothed or often three to seven times lobed, cut or divided. Most of the leaf surfaces are bare, rarely hairy, and the tip is rounded to pointed. The leaves are mostly green in color, but the accumulation of anthocyanins, especially along the leaf veins, can make them purple. Depending on the variety, the total length of a stem can be between. Some cultivars also form shoots up to in length. However, these do not form underground storage organs.The hermaphrodite, five-fold and short-stalked flowers are single or few in stalked, zymous inflorescences that arise from the leaf axils and stand upright. It produces flowers when the day is short. The small sepals are elongated and tapering to a point and spiky and long, usually finely haired or ciliate. The inner three are a little longer. The long, overgrown and funnel-shaped, folded crown, with a shorter hem, can be lavender to purple-lavender in color, the throat is usually darker in color, but white crowns can also appear. The enclosed stamens are of unequal length with glandular filaments. The two-chamber ovary is upper constant with a relatively short stylus. Seeds are only produced from cross-pollination.
The flowers open before sunrise and stay open for a few hours. They close again in the morning and begin to wither. The edible tuberous root is long and tapered, with a smooth skin whose color ranges between yellow, orange, red, brown, purple, and beige. Its flesh ranges from beige through white, red, pink, violet, yellow, orange, and purple. Sweet potato cultivars with white or pale yellow flesh are less sweet and moist than those with red, pink or orange flesh.
Taxonomy
The sweet potato originates in South America in what is present-day Ecuador. The domestication of sweet potato occurred in either Central or South America. In Central America, domesticated sweet potatoes were present at least 5,000 years ago, with the origin of I. batatas possibly between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela. The cultigen was most likely spread by local people to the Caribbean and South America by 2500 BCE.I. trifida, a diploid, is the closest wild relative of the sweet potato, which originated with an initial cross between a tetraploid and another diploid parent, followed by a second complete genome duplication event. The oldest radiocarbon dating remains of the sweet potato known today were discovered in caves from the Chilca Canyon, in the south-central zone of Peru, and yield an age of 8080 ± 170 BC.
Transgenicity
The genome of cultivated sweet potatoes contains sequences of DNA from Agrobacterium, with genes actively expressed by the plants. The T-DNA transgenes were not observed in closely related wild relatives of the sweet potato. Studies indicated that the sweet potato genome evolved over millennia, with eventual domestication of the crop taking advantage of natural genetic modifications. These observations make sweet potatoes the first known example of a naturally transgenic food crop.Cultivation
Dispersal history
Before the arrival of Europeans to the Americas, sweet potato was grown in Polynesia, generally spread by vine cuttings rather than by seeds. Sweet potato has been radiocarbon-dated in the Cook Islands to 1210–1400 CE. A common hypothesis is that a vine cutting was brought to central Polynesia by Polynesians who had traveled to South America and back, and spread from there across Polynesia to Easter Island, Hawaii and New Zealand. Genetic similarities have been found between Polynesian peoples and indigenous Americans including the Zenú, a people inhabiting the Pacific coast of present-day Colombia, indicating that Polynesians could have visited South America and taken sweet potatoes prior to European contact. Dutch linguists and specialists in Amerindian languages Willem Adelaar and Pieter Muysken have suggested that the word for sweet potato is shared by Polynesian languages and languages of South America: Proto-Polynesian *kumala may be connected with Quechua and Aymara k'umar ~ k'umara. Adelaar and Muysken assert that the similarity in the word for sweet potato is near proof of either incidental contact or sporadic contact between the Central Andes and Polynesia.Some researchers, citing divergence time estimates, suggest that sweet potatoes might have been present in Polynesia thousands of years before humans arrived there. However, the present scholarly consensus favours the pre-Columbian contact model.
The sweet potato arrived in Europe with the Columbian exchange. It is recorded, for example, in Elinor Fettiplace's Receipt Book, compiled in England in 1604.
Sweet potatoes were first introduced to the Philippines during the Spanish colonial period via the Manila galleons, along with other New World crops. It was introduced to the Fujian of China in about 1594 from Luzon, in response to a major crop failure. The growing of sweet potatoes was encouraged by the Governor Chin Hsüeh-tseng.
Sweet potatoes were also introduced to the Ryukyu Kingdom, present-day Okinawa, Japan, in the early 1600s by the Portuguese. Sweet potatoes became a staple in Japan because they were important in preventing famine when rice harvests were poor. Aoki Konyō helped popularize the cultivation of the sweet potato in Japan, and the Tokugawa bakufu sponsored, published, and disseminated a vernacular Japanese translation of his research monograph on sweet potatoes to encourage their growth more broadly. Sweet potatoes were planted in Shōgun Tokugawa Yoshimune's private garden. It was first introduced to Korea in 1764. Kang P'il-ri and Yi Kwang-ryŏ embarked on a project to grow sweet potatoes in Seoul in 1766, using the knowledge of Japanese cultivators they learned in Tongnae starting in 1764. The project succeeded for a year but ultimately failed in winter 1767 after Kang's unexpected death.
Names
Although the soft, orange sweet potato is often called a "yam" in parts of North America, the sweet potato is distinct from the botanical yam, which has a cosmopolitan distribution, and belongs to the monocot family Dioscoreaceae. A different crop plant, the oca, is called a "yam" in many parts of the world.Although the sweet potato is not closely related botanically to the common potato, they have a shared etymology. The first Europeans to taste sweet potatoes were members of Christopher Columbus's expedition in 1492. Later explorers found many cultivars under an assortment of local names, but the name which stayed was the indigenous Taíno name of batata. The Spanish combined this with the Quechua word for potato, papa, to create the word patata for the common potato.
Though the sweet potato is also called batata in Hebrew, this is not a direct loan of the Taíno word. Rather, the Spanish patata was loaned into Arabic as batata, owing to the lack of a sound in Arabic, while the sweet potato was called batata ḥilwa ; literally. The Arabic batata was loaned into Hebrew as designating the sweet potato only, as Hebrew had its own word for the common potato, .
Some organizations and researchers advocate for the styling of the name as one word—sweetpotato—instead of two, to emphasize the plant's genetic uniqueness from both common potatoes and yams and to avoid confusion of it being classified as a type of common potato. In its current usage in American English, the styling of the name as two words is still preferred.
In Argentina, Colombia, Venezuela, Puerto Rico, and the Dominican Republic, the sweet potato is called batata. In Brazil, the sweet potato is called batata doce. In Mexico, Bolivia, Peru, Chile, Central America, and the Philippines, the sweet potato is known as camote, derived from the Nahuatl word camotli.
In Peru and Bolivia, the general word in Quechua for the sweet potato is apichu, but there are variants used such as khumara, kumar, and kumara, strikingly similar to the Polynesian name kumara and its regional Oceanic cognates, which has led some scholars to suspect an instance of pre-Columbian trans-oceanic contact. This theory is also supported by genetic evidence.
In Australia, about 90% of production is devoted to the orange cultivar 'Beauregard', which was originally developed by the Louisiana Agricultural Experiment Station in 1981.
In New Zealand, the Māori varieties bore elongated tubers with white skin and a whitish flesh, which points to pre-European cross-Pacific travel. Known as kumara, the most common cultivar now is the red 'Owairaka', but orange, gold, purple and other cultivars are also grown.