Sweet potato cultivation in Polynesia began around 1000 AD in central Polynesia. The plant became a common food across the region, especially in Hawaii, Easter Island and New Zealand, where it became a staple food. By the 17th century in central Polynesia, traditional cultivars were being replaced with hardier and larger varieties from the Americas (a process which began later in New Zealand, in the early 19th century). Many traditional cultivars are still grown across Polynesia, but they are rare and are not widely commercially grown.
It is unknown how sweet potato began to be cultivated in the Pacific. Some scholars suggest that the presence of sweet potato in Polynesia is evidence of Polynesian contact with South America. However, some genetic studies of traditional cultivars suggest that sweet potato was first dispersed to Polynesia before human settlement.
History
The sweet potato plant (Ipomoea batatas) is originally from the Americas, and became widely cultivated in Central and South America by 2500 BC. Sweet potato is thought to have been first grown as a food crop in central Polynesia around 1000–1100 AD, with the earliest archaeological evidence being fragments recovered from a single location on Mangaia in the southern Cook Islands, carbon dated between 988 and 1155 AD. Over the next few centuries, sweet potato was spread to the extremes of the Polynesian Triangle: Easter Island, Hawaii and New Zealand. Sweet potatoes may have spread so rapidly in the Pacific because Polynesian gardeners saw these plants as an improvement on already grown Dioscorea species, such as the purple yam. The plant was likely spread between Polynesian islands by vine cuttings rather than by seeds.
The prevailing theory for the lineages of sweet potato seen in Polynesia is the tripartite hypothesis developed in the 1950s and 1960s: that an original lineage was brought from the west coast of South America circa 1000 AD, and later superseded by two lineages introduced by Spanish galleons and Portuguese traders circa 1500 AD, the Central American lineage and the Caribbean lineage. Sweet potato became a major staple more so at the extremities of Polynesian culturesuch as in pre-European contact Hawaii, Easter Island and New Zealandthan in central Polynesia. During the 1600s, traditional Polynesian cultivars of sweet potato and calabash began to be replaced with North American varieties. During reintroduction, the sweet potato had become entirely absent from many central Polynesian islands (such as the Cook Islands, except Mangaia).
Pre-Columbian contact theory
Some researchers cite the presence of the sweet potato in the Pacific as evidence of sporadic contact between Polynesian and Native American peoples. However, it is unknown whether sweet potato was introduced through Polynesian canoes reaching South America, or by South American rafts visiting eastern Polynesian islands such as Rapa Nui. It is also possible that the plant was transferred without human contact, such as floating west across the ocean after being discarded from the cargo of a boat.
Genetic, cultural or linguistic links between Polynesian and Indigenous American peoples such as the Chumash people of California, the Mapuche in central and southern Chile, and the Zenú, a pre-Columbian culture of Colombia, have been hypothesised. Dutch linguists and specialists in Indigenous American 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 * (compare Rapa Nui , Hawaiian , Māori ) may be connected with Quechua and Aymara ~ . Adelaar and Muysken assert that the similarity in the word for sweet potato is proof of either incidental contact or sporadic contact between the Central Andes and Polynesia.
Natural dispersal theory
Some researchers suggest that sweet potatoes might have been present in Polynesia thousands of years before humans arrived there, arriving through avian dispersal or natural rafts. A 2018 genetic analysis of sweet potato collected from the Society Islands by Joseph Banks during the first voyage of James Cook in 1769 found this lineage diverged from South American varieties at least 111,500 years ago. The paper's authors also argued a natural dispersal was likely due to the presence of Ipomoea littoralis and Ipomoea tuboides in the Pacific and Asia — species which are related to American Ipomoea species that have similar seed morphology to sweet potatoes.
Regional introductions Introduction to Hawaii
On the Hawaiian Islands, the earliest archaeological record of sweet potatoes () is circa 1300 AD, where traces were found on traditional farmlands of Kohala, Hawaii. Sweet potato was likely introduced to the islands at a later point, after initial Polynesian settlers had arrived. Sweet potato was considered to be less superior or valuable compared to another crop on the islands, taro, but it was commonly grown as it could flourish in less favourable growing conditions, and only took between three and six months to mature.
Introduction to Easter Island
Sweet potato () was introduced to Easter Island (Rapa Nui) around 1200–1300 AD. The crop, due to its drought-resistant nature, replaced yam and taro, becoming the staple food on the island and grown on 1/10th of the total land on the island. A traditional Rapa Nui legend involves Hotu Matuꞌa, the legendary first settler of Rapa Nui, travelling to the island and planting sweet potato, yam and bottle gourds near Orongo.
It has been hypothesised that the introduction of sweet potato to the island directly led to the construction of platforms and moai statues, as the large harvests would have meant the island's inhabitants were able to dedicate more time to activities other than subsistence farming. The introduction of sweet potato to the island may have also led to the deforestation of Easter Island, as burnt palm forest was a source of nutrients necessary for the growth of sweet potatoes in nutrient-poor soil.
Introduction to New Zealand
Sweet potato (standard Māori: , Southern Māori dialects: ) is a traditional crop for Māori. Archaeological evidence suggests that kūmara arrived in New Zealand after the original Polynesian voyagers had settled in New Zealand, likely sometime between 1300 and 1400. Lack of archaeological evidence on the abandoned Māori settlements on Raoul Island and Norfolk Island implies kūmara was not available in the early 1300s. Oral histories tell of a return voyage to central Polynesia to collect the plant for use in New Zealand, but oral histories do not agree on a single voyage or source: the introduction of kūmara is associated with the Aotea, Arawa, Horouta, Kurahaupō, Māhuhu, Māmari, Mātaatua, Tainui and Tokomaru canoes, possibly due to the associated with having brought kūmara to New Zealand. One history involves Tūhoe ancestor Toi-kai-rākau, who, after he sailed the Horouta to New Zealand, introduced local Māori to dried kūmara (). The locals, having loved the vegetable, sailed on the Horouta back to central Polynesia to collect the plant to grow in New Zealand. Ngāti Awa have a similar stories about the Mātaatua , that it was sent to bring kūmara supplies to Whakatāne. In Tainui and Te Arawa traditions, kūmara was brought to New Zealand by Whakaotirangi, a woman who carried seeds of important plants on the journey to New Zealand after being kidnapped by the chief Tama-te-kapua, around 1350 AD. Whakaotirangi experimented with ways to adapt growing kūmara in the colder climate, where they would develop an unpleasant sour taste when exposed to frost. Another history involves Marama, the junior wife of Hoturoa aboard the Tainui . She brought kūmara plants with her on her journey, but, when she arrived in Aotearoa, she was unfaithful to Hoturoa with a slave. As punishment, her kūmara plants turned into (Calystegia sepium)a traditional weed of kūmara farms.
In 1880, botanist and missionary William Colenso listed 48 varieties grown in Northland, Hawke's Bay and the East Coast. These traditional varieties came in a variety of colours (red, purple and white), shapes (some cylindrical) and differing rough/smooth textures. Northland Māori described a red-fleshed, red-skinned variety called as the oldest variety of kūmara to Colenso, while Te Arawa sources in the 1940s called and the oldest varieties. Kūmara does not seed in New Zealand due to the climate, meaning mutations in buds and careful cultivation of these plants likely led to the new varieties. A 1955–1959 survey of Māori farmers identified four cultivars considered to be pre-European: and (grown in Northland), and two closely related varieties grown across the North Island: and ( and were commonly grown in Māori home gardens until the 1940s). A 1997 DNA analysis of these varieties confirmed that , and are all pre-European ( was not tested in the study). Other traditional cultivars outside of this list still exist, such as (a variety used for medicinal reasons to feed the elderly, babies and the unwell), (used to make ), , and .
Cultivation and use Hawaii
Sweet potato on the Hawaiian islands was typically grown in (stony alluvial soils), and in arid/coastal areas. Many (cultivations) were planted as a mix of sugarcane () and sweet potato, with sugarcane planted in rows alongside the stone field walls to act as a windbreak for the sweet potato crop planted in between these rows. Often sweet potato was planted in mounds, with the soil mulched with a mix of rocks and plants. Rats preyed on the sweet potato crops during the Hawaiian rainy season (November to March), while periodic outbreaks of Sphingidae moth caterpillars, cutworms and weevils would greatly damage crops. Sweet potato is associated with the new year festival of , where the first fruits of the harvest () were offered to the gods, typically sweet potatoes and taro.
By the mid-1800s, traditional rain-fed sweet potato cultivation in Hawaii ceased due to depopulation and damage caused by introduced Western grazing animals. Since the early 1900s, pests were introduced to the islands which impacted farmers' abilities to grow sweet potato in Hawaii, such as Cylas formicarius (the sweet potato weevil) and Omphisa anastomosalis (the sweet potato vine borer). This is to the degree that farmers often refrain from planting sweet potato in the same location for two successive seasons. Sweet potato became a major export crop for Hawaii in the 20th century, although since the 1990s the number of plantations has decreased.
There are over 300 different names for traditional sweet potato varieties, with many names likely being synonyms for the same varieties. Some of the most commonly cited in ethnographies and traditional sources include apo, huamoa, kawelo, likolehua and uahi-a-pele. Huamoa is a variety described as egg-like, being round, with a white skin and a yellow flesh. Most sweet potatoes produced in Hawaii are modern imported varieties, such as the Okinawa purple variety, however several heritage cultivars that are still grown are likely pre-European cultivars, including , and purple .
Easter Island
Sweet potato planting typically occurs twice a year, from January to April and August to September. Lithic mulching (mixing rocks into fertile soil) was used by traditional Rapa Nui gardeners in order to retain moisture in sweet potato plantations. Plants are typically grown from grafts taken from mature plants, and take from between 120 and 180 days to mature. The end of the initial stage involves piling earth on top of the plants. Sweet potato was not often stored on Rapa Nui, instead typically eaten directly after harvesting. Occasionally sweet potatoes were stored for festivals or ceremonies, by drying large tubers in the sun, then burying them in soil for up to one month. Sweet potatoes were eaten raw or cooked. The young leaves of the sweet potato are also eaten.
New Zealand