Information on East Africa is the most speculative, and there are no concrete details on the date of cassava's introduction. We must assume that, as in West and Central Africa, it was introduced at the Portuguese trading stations: Mozambique, Benguela, Sofala, Kilwa, Zanzibar, Pemba and Mombassa, during the 17th or 18th centuries. In Figure 1 we have assumed the latter period.

Pasch (1980) reports that cassava was brought to the country of South Africa as early as the 16th century, probably from Mozambique, suggesting a long presence in the area, but this is not commonly accepted by inlanders.

Alpers (1975) claims that the first introduction in Mozambique was from Moçambique Island in 1768, although the crop could have been introduced from other areas in mainland Mozambique.

Cassava was probably introduced to Madagascar during the 18th century, prior to 1750, according to Kent (1969). This author even proposed a 16th century introduction to the island. It appears to have spread inland rapidly, being reported at Imerina near Fianarantsoa in 1785.

In Mozambique, Portuguese colonists and their African descendants were probably responsible for diffusion in the lower Zambezi Valley, but we know from Wood (1985) that cassava reached the upper Zambezi from Angola rather than Mozambique. Similarly, cassava reached Lake Tanganyika from the west, rather than the east.

Jones (1959) underlines the importance of the environmental and cultural barriers presented by the East African plains and their warlike and nomadic peoples in preventing cassava's diffusion.

In view of the successful introduction in Central Africa, it seems therefore less likely that cassava diffused along the eastern shores of Lakes Malawi and Tanganyika to the highlands of Rwanda and Burundi.

Rather, the crop may have come from the west or may, simultaneously, have spread to the highlands after being introduced in the Lake Victoria region by Arab traders, as Jones (1959) and Langlands (1966) believe. In any case, cassava was reported widely throughout the Great Lakes Region by numerous travelers in the mid-19th century. In 1883, cassava was introduced to southern Sudan by the Iddis peoples.

The most detailed information on diffusion in East Africa is that of Langlands for Uganda. It was first recorded in Buganda, north of Lake Victoria, in 1862. After its initial introduction, cassava spread only slowly. It seems that bananas were preferred as a staple.

In the first half of the 20th century, the role of the colonial administrators was central to the spread of cassava in western and northern Uganda, particularly as a famine reserve crop.

In Rwanda, Kamanzi (1983) attributes the introduction of cassava in the 1930s to the colonial administration. However, it is difficult to believe that it did not arrive from the west, if not the south, during the 19th century.

Meyer (1984) described cassava cultivation in Burundi in his journeys around 1911. He noted that sweet varieties were important, and that it was consumed in a number of different forms. This suggests considerable familiarity-inconsistent with Kamanzi's hypothesis of more recent introduction.

Similarly, we cannot exclude the possibility that cassava was already known in some parts of East Africa prior to the 20th century, without becoming an important staple crop. The reasons have to be explored, but the need for another staple may have been less pressing, or processing techniques may have been unknown. One example is among the southern Kikuyu in Kenya. Cassava was present before 1903, but was only used for medicinal or magical purposes.

In coastal Kenya, in 1911, it was reported that the primary local diet consisted of 'palm wine, cassava and mangoes, either alone or in combination', during a drought. In this latter case, whilst it is not clear whether cassava was a staple under normal conditions, its usefulness as a famine reserve was clearly recognized by local people.

From Mozambique, cassava was taken southward to its climatic limit along the eastern coast of southern Africa, also during the 19th century. Whilst relatively unimportant, it is today found in north-east Transvaal and northern Zululand.