The sweet potato belongs to the morning glory family, Convolvulaceae, a kinship that surprises all who first encounter it: the delicate trumpet-shaped flowers of the sweet potato vine are unmistakably of a piece with the bindweeds and convolvulus that scale garden walls, and the plant's twining, ground-covering habit reveals its ancestry clearly in any cultivated field. Yet from this herbaceous vine comes one of the most nutritionally significant storage roots on earth, a swollen underground tuber that has fed more people through more famines in more climates than perhaps any other single cultivated plant.

The earliest archaeological evidence for sweet potato cultivation comes from the coastal valleys of Peru and Ecuador, where carbonised remains from the Ica Valley and the Chilca Canyon have been dated to approximately 8000 BCE, making the sweet potato one of the oldest cultivated crops in the Americas. The wild progenitor species of Ipomoea batatas are found in the region extending from southern Mexico through Central America and into northwestern South America, and genetic analyses suggest the crop may have been brought into cultivation independently in both the Andean-coastal zone and the Mesoamerican zone, the two lineages subsequently intermingling through millennia of trade. By the time of European contact, the Americas supported an extraordinary diversity of sweet potato cultivars, named and selected for particular soils, storage properties, and culinary uses.

Ipomoea batatas is a hexaploid — it carries six sets of chromosomes rather than the two of most familiar crop plants — a genomic complexity that reflects its convoluted domestication history and underlies the remarkable diversity of its forms. The cultivated sweet potato exists in a spectrum of flesh colours from white and cream to pale yellow, deep orange, vivid red, and the dark purple of the Okinawan beni imo and the Japanese Murasaki Imo, each colour produced by a different assemblage of pigments with distinct nutritional and culinary properties. Orange flesh is richest in beta-carotene, converting efficiently to vitamin A in the body; purple flesh derives its colour from anthocyanins; white and cream-fleshed varieties are drier, starchier, and more neutral in flavour, preferred across much of Asia and the Pacific. This diversity of form is the product of several thousand years of sustained selective cultivation across three continents, and it makes the sweet potato one of the most versatile food plants in the world.

The sweet potato achieved one of the most remarkable dispersals in the history of cultivated plants, and it did so in two distinct phases: a pre-Columbian oceanic crossing that modern genetic science has only recently confirmed, and a post-Columbian global expansion that ranks among the fastest and most consequential crop diffusions in history.

The pre-Columbian dispersal is the more extraordinary. When European explorers reached the Pacific islands, they found sweet potato already growing there: in the Marquesas, in the Society Islands, in Hawaii, and, most significantly, in Aotearoa New Zealand, where the Māori called it kūmara and cultivated it as a staple of the highest cultural importance. The Māori word kūmara and the Quechua word kumara are near-identical, and this is not coincidence: a 2020 genetic study by Muñoz-Rodríguez and colleagues confirmed that the Polynesian sweet potato derived from South American cultivar populations that diverged from their Andean ancestors around 1000–1100 CE, and that the introduction most likely occurred through a direct encounter between Polynesian voyagers and the peoples of South America in the eastern Pacific. The sweet potato became the only food plant, apart from the bottle gourd, for which pre-Columbian contact between the peoples of the Pacific and the Americas is scientifically proven.

The European chapter began on Hispaniola, where Columbus encountered the plant on his first voyage in 1492–93. The Taíno people called it batata, and this word — not the sweet potato itself — was eventually transferred to the white potato (Solanum tuberosum) when that plant arrived from South America decades later, giving both unrelated tubers the same etymological root and creating the nomenclatural confusion that persists in English as 'potato' and in the American South as 'yam'. By the early sixteenth century the plant was established in the gardens of Spain and Portugal, with the Canary Islands becoming the first sustained Old World farming region for the crop.

From Spain and Portugal the sweet potato spread in two directions. Portuguese traders carried it along the West African coast, arriving in the Senegambia region around 1580 and spreading eastward through the Guinea coast and into central and eastern Africa, eventually becoming one of the most important food security crops in sub-Saharan Africa. Eastward, the plant reached Asia through the Manila Galleon trade: Spanish ships loaded sweet potato at Acapulco in New Spain and carried it to Manila in the Philippines, where it became the kamote, a dietary staple and the transit point for the plant's most consequential Asian journey.

From Manila in 1594, a Chinese merchant named Chen Zhenlong smuggled sweet potato slips past Spanish colonial prohibitions and carried them to Fujian Province, then in the grip of a devastating famine. The provincial governor, Jin Xuezeng, immediately promoted their cultivation throughout Fujian; the famine was broken, and the sweet potato spread across southeastern China with a speed that reflects the hunger it was meeting. China became and remains the world's largest producer, harvesting over sixty per cent of global output.

From Fujian, the plant reached the Ryūkyū Kingdom (modern Okinawa) around 1605, carried by a local official named Noguni Soukan, and from Okinawa it was introduced to the Satsuma Domain of mainland Japan around 1700, acquiring the name Satsumaimo in the process. In Korea it arrived as goguma through Joseon-era trade with Japan, recorded by the official Cho Eom in 1763. In the Americas, sweet potatoes were established in the Virginia colony by 1648 and became inseparable from the cooking of enslaved African Americans, who applied their agricultural knowledge of root-crop traditions to the new plant and gave it, in the American South, the name 'yam' — borrowed from West African words for the true yam of their homeland.

China is overwhelmingly the world's largest producer of sweet potatoes, accounting for over sixty per cent of global output; the roasted sweet potato vendor is one of the most characteristic figures of the Chinese winter street scene, and the sweet potato appears across the Chinese kitchen in forms from congee to dessert soups to the spectacular caramelised theatre of bā sī hóng shǔ, sweet potato in spun-sugar toffee threads. Sub-Saharan Africa is the world's second major zone of production and consumption, with Uganda recording among the highest per-capita consumption on earth; the orange-fleshed sweet potato has been the focus of public health programmes addressing vitamin A deficiency across East and Central Africa, harnessing the tuber's exceptional beta-carotene content as a nutritional intervention at the smallholder level.

Japan and Korea maintain sophisticated and distinct sweet potato cultures. The Japanese Satsumaimo, with its vivid red-purple skin and pale, intensely sweet yellow flesh, is the basis of the celebrated daigaku imo and the yakiimo, the baked sweet potato sold from drum-oven carts at autumn festivals. In Okinawa, the purple beni imo has become one of Japan's most recognisable regional food products, used in tarts, mochi, ice cream, and the distilled spirit imo-jōchū. Korea's goguma is roasted as street food, candied as mattang, and stirred into rice and pancakes.

In the Americas, the sweet potato remains central to the food cultures of both its origin and its adoption. Peru preserves ancient preparations in the form of the mazamorra de camote; Mexico marks the Day of the Dead with camotes en tacha, the whole sweet potatoes candied in piloncillo and orange. The Southern United States' sweet potato pie is the most fiercely partisan dish at the holiday table, distinct in character from the pumpkin pie with which outsiders confuse it, and carrying a cultural history inseparable from the African American communities who made it their own. In Aotearoa New Zealand, the Māori kūmara is maintained by Māori growers as both a living agricultural practice and a connection to the pre-Columbian navigational achievement that brought the plant across the Pacific a thousand years before European botanists arrived to describe it.