In 1930, a British district officer named William Giliat Cragg travelled from New Zealand to Nigeria with eight sweet potatoes tucked into his luggage. The large red tubers, known as kūmara in the Māori language, were then incorporated into a six-year project of botanical research and agricultural trials centred around a colonial research post in Samaru. This research eventually resulted in ‘Cragg’s Red’, a strain that became popular across the territory. The records of these trials, now held at the Kaduna branch of the National Archives of Nigeria, are worth reading critically and closely. Together, they reveal a pattern that has never really gone away: scientific discoveries are usually attributed to those who write the reports, rendering other kinds of labour invisible. That is as true of today’s seed banks and genetic databases as it was in Cragg’s Nigeria.
Sweet potato reached West Africa long before Cragg was born, carried by Portuguese traders in the sixteenth century as part of the vast global shuffling of crops now known as the Columbian Exchange. By the twentieth century, sweet potato was so embedded in Nigerian farming that people treated it as a native crop. The kūmara had a different journey. It was first grown in the Andes, and spread through the Pacific along Polynesian voyaging routes, and was cultivated and named by Māori communities in Aotearoa before being absorbed into New Zealand’s settler colonial system. Cragg, who had previously lived in a settlement on the North Island, then carried the kūmara into a very different system: the Colony and Protectorate of Nigeria, where he worked as a member of the imperial administration.
Cragg was not acting alone. Moving plants between colonies was standard practice for British colonial officials, who helped to coordinate networks of plants, personnel and correspondence across the empire. In the late nineteenth century, institutions like the Royal Botanic Gardens at Kew had already moved rubber from Brazil to Malaya and cinchona from the Andes to India. Cragg’s project also belonged to a wider effort to ‘improve’ and commercialise African agriculture. By the early 1900s, Northern Nigeria had become a site of experimentation, from breeding cotton strains to farming ostriches so their feathers could be used for luxury hats. These campaigns were often carried out through the local emirs on whom the colonial administration relied. The correspondence in the National Archives in Kaduna gives little indication of how freely a farmer could refuse a crop an Emir had promoted.
When Cragg arrived in Nigeria, he reserved five of the kūmara tubers for his own garden and sent the other three to researchers in Samaru. From there, the real agricultural work began. Local station staff, whose names were not recorded, planted and tended seedlings through the rains, running trials against other sweet potato varieties. From that point on, Cragg’s role was almost entirely confined to writing letters: asking for updates and asking whether the crop was worth anything. He was still corresponding with the Samaru station in September 1935, three years after his retirement, to ask whether local people could be induced to grow them, claiming that he was promoting the strain ‘at a considerable personal expense’.
Nigerian station staff, meanwhile, were busy judging the crop for themselves. Trials found kūmara to be sweeter than local varieties, but lower yielding. When the strain that would eventually become ‘Cragg’s Red’ was transferred south to Ibadan, it proved popular because it matured earlier than local varieties, but it still produced less than the white and red varieties already grown there. Kūmara also had to compete with the American and West Indian varieties being tested at Moor Plantation in Ibadan, becoming one import within an imperial bureaucracy that was interested in testing and redistributing new crops across Nigeria.
Nigerian farmers were also conducting tests of their own. By 1935, kūmara had spread to farms near Samaru without displacing the higher-yielding dakata and maiyatsa strains, themselves relatively recent arrivals that had displaced older cultivars. Here, too, kūmara had to compete with a wide range of local crops. In 1936, a survey of agricultural officers across nine provinces mentions a wide variety of sweet potato varieties. Among the Tiv in Benue Province, farmers grew Atsaka, Tor Atsaka and Nyigha Nyigha. In Katsina, it was Dakata Uwardi, Lawan and Frain Dankali. Correspondence about the kūmara records, almost as an afterthought, a whole geography of crops that were being cultivated before Cragg had even left New Zealand. The cultivators of these strains, however, are generally unnamed. Tellingly, one of the only Nigerians mentioned in the files is Ibrahim ibn Muhammad Lawal Kwassau, the influential Emir of Zazzau, and he appears in the archive only because Cragg wanted his support in mobilising local farmers to embrace the kūmara.
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Cragg’s letters, with their claims of ‘considerable personal expense’, try to tell a story of his individual persistence winning out. Their prominence in the colonial archive, and the use of the name ‘Cragg’s Red’ for the strain that was produced, centres his initiative at the expense of the Nigerian labourers who made it possible. In reality, Nigerian farmers were running their own repeated trials against a rotating cast of new arrivals. The habit of naming a variety after administrators rather than the labourers who developed it continues to this day. It is part of the same pattern that international agreements like the Nagoya Protocol are now trying to correct by introducing rules about who gets credited and compensated when a crop bred by farmers over generations is commercialised by an outside institution. In 2019, for instance, South Africa’s rooibos industry signed a benefit-sharing agreement with Khoi and San representatives, acknowledging that a now-global crop rested on knowledge produced by people who had never been credited or paid. The FAO’s Plant Treaty, which covers staple crops including sweet potato, now provides a multilateral system that protects access to cultivars and shares benefits through a common fund. As seed banks like the Svalbard Global Seed Vault and the gene banks of the Consultative Group on International Agricultural Research continue to circulate and store crop varieties, however, it is still necessary to think critically about who gets credited and when.
Cragg wrote letters, so Cragg survives in the archive. The nursery workers at the experimental station in Samaru who kept his tubers alive, the botanists who ran years of trials, the farmers around Zaria who tested the results and made their own judgements, and the Emir Cragg hoped to enlist, all appear only as background detail, if they appear at all. The story of Cragg’s kūmara is, in this sense, a precise example of something much larger: five centuries of crops moving through colonial systems, their development credited mostly to whoever was literate and close enough to power to leave a letter behind. The same choices about credit, about whose evaluation counts and about what gets recorded, are still being made today, in the institutions deciding how the next seed banks or genetic databases get built.