Is a yam a sweet potato?

This is a question which requires both a ‘yes’ and a ‘no’ answer. Starting with ‘no’, in strictly botanical terms, yams and sweet potatoes are completely different plants and vegetables.

The yam is the edible tuber of a climbing plant of the genus Dioscorea (family Dioscoreaceae), of which there are many species and varieties. Yams are of West African or Asian origin and have a rough brown, pink, or purple skin, while their flesh is typically white or yellowish in colour, with a rather dry texture. People chiefly eat yams for their carbohydrate content: they are starchy and filling, just like bread, potatoes, rice, and pasta.

The sweet potato is the tuber of a climbing plant from South or Central America, Ipomoea batatas: it belongs to the Convolvulaceae family, which includes the closely related morning glory, as well as bindweed. Sweet potatoes typically have a smooth orange, pinkish-red, or brown skin and yellow, beige, orange, or white flesh.  This flesh is also moist and fairly sweet, and can be prepared in many ways, from roasting to frying: in some countries (such as Spain and the USA), sweet potatoes also form the basis for some dessert pies and cakes.

Returning to the original question, if you live in North America, you would respond with a ‘yes’ when asked ‘Is a yam a sweet potato?’. According to the Library of Congress , some varieties of sweet potato stay firm when cooked, while others become soft and moist. In former times, African slaves in the US called the ‘soft’ sweet potatoes ‘yams’ because they reminded them of the ‘true’ African yams. It then became general usage in North America to refer to the soft varieties of sweet potatoes as ‘yams’ to distinguish them from the firmer varieties. 

In fact, ‘yam’ seems to be a multi-purpose term, cropping in different places as a name for a range of starchy vegetables. For instance, ‘yam’ is used to describe taro in Malaysia and Singapore, and according to the Oxford English Dictionary, the good old potato (Solanum tuberosum) was once called a‘yam’ in Scotland.


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