Yam Discussion
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A tuber of African origin, allied to the sweet potato, but with moist
texture and high sugar content, and a whitish to reddish color skin and
greenish-yellow to reddish or orange tint flesh. There is a wide variation
in shape. The yam closely resembles the sweet potato, but grows much
larger; it is the tuberous root of a different plant.

From The Wise Encyclopedia of Cookery.