Sweet potato

The sweet potato (Ipomoea batatas) is a dicot plant belonging to the morning glory family, Convolvulaceae. It produces large, starchy, sweet-tasting tuberous roots that are eaten as a root vegetable and serve as a dietary staple in various regions. Native to tropical South America, specifically modern-day Ecuador, it is the only major crop plant among the roughly 50 genera and over 1,000 species in its family, though water spinach (Ipomoea aquatica) is also used locally as a green.

The plant is a herbaceous perennial vine with stems that typically crawl along the ground, forming adventitious roots at the nodes. Its leaves are arranged alternately along the stems, with leaf stalks 13 to 51 centimeters long. The leaf blades vary widely in shape—heart-shaped, kidney-shaped, egg-shaped, rounded, triangular, or spear-shaped—and can be entire, toothed, or lobed three to seven times. They are usually hairless, rarely hairy, and range from 5 to 13 centimeters in length, with tips that are rounded or pointed. Most leaves are green, but anthocyanin accumulation, especially along veins, can turn them purple. Stems can reach 0.5 to 4 meters in total length, with some cultivars producing shoots up to 16 meters long that do not form underground storage organs.

The flowers are hermaphroditic, five-parted, and short-stalked, appearing singly or in small clusters in upright, stalked inflorescences from the leaf axils. They bloom only when days are short, opening before sunrise and closing a few hours later in the morning. The sepals are elongated, tapering to a point, 10 to 15 millimeters long (rarely 7 millimeters), and often finely hairy. The funnel-shaped crown is 4 to 7 centimeters long, with a shorter hem, and is lavender to purple-lavender, though white crowns occur; the throat is usually darker. Stamens are enclosed, of unequal length, with glandular filaments, and the two-chambered ovary has a relatively short style. Seeds result only from cross-pollination.

The edible tuberous root is long and tapered, with smooth skin in colors ranging from yellow, orange, red, brown, purple, to beige. Its flesh can be beige, white, red, pink, violet, yellow, orange, or purple. Cultivars with white or pale yellow flesh are less sweet and moist than those with red, pink, or orange flesh. Young shoots and leaves are also eaten as greens. Although darker sweet potatoes are often called yams in parts of North America, they are only distantly related to true yams, which are monocots in the order Dioscoreales; sweet potatoes and potatoes are also distantly related, both in the order Solanales.

The sweet potato originated in South America, in present-day Ecuador. Domestication occurred in either Central or South America, with domesticated sweet potatoes present in Central America at least 5,000 years ago, possibly originating between Mexico’s Yucatán Peninsula and Venezuela’s Orinoco River mouth. The cultigen likely spread to the Caribbean and South America by 2500 BCE. The closest wild relative is *Ipomoea trifida*, a diploid; the sweet potato itself arose from an initial cross between a tetraploid and another diploid parent, followed by a second complete genome duplication. The oldest known radiocarbon-dated remains, from caves in Peru’s Chilca Canyon, date to 8080 ± 170 BC.

The cultivated sweet potato’s genome contains DNA sequences from *Agrobacterium* (specifically related to *Rhizobium rhizogenes*), with genes actively expressed by the plant. These T-DNA transgenes are absent in closely related wild relatives. Studies suggest the genome evolved over millennia, with domestication taking advantage of these natural genetic modifications, making sweet potatoes the first known naturally transgenic food crop.

Before Europeans arrived in the Americas, sweet potato was grown in Polynesia, spread by vine cuttings rather than seeds. It has been radiocarbon-dated in the Cook Islands to 1210–1400 CE. A common hypothesis is that Polynesians brought a vine cutting to central Polynesia after traveling to South America and back, spreading it across Polynesia to Easter Island, Hawaii, and New Zealand. Genetic similarities between Polynesian peoples and indigenous Americans, including the Zenú of present-day Colombia’s Pacific coast, suggest Polynesians may have visited South America and taken sweet potatoes before European contact. Some cultivars of *I. batatas* are grown as ornamental plants, called tuberous morning glory, and the term "yam" is sometimes used for sweet potatoes in North America.