Okinawan sweet potatoes, sometimes called Japanese purple potatoes, or Japanese sweet potatoes, are a unique variety of sweet potato which is actually native to the Americas, not Japan, let alone Okinawa. These sweet potatoes have become famous and very distinctive because of their richly colored flesh, which happens to be a vibrant purple, in a marked contrast to the dull tan skins of this produce item. Okinawan sweet potatoes can be used in a wide assortment of dishes, and they are especially popular in Japan and Hawaii.
Before we delve into the specifics of the Okinawan sweet potato, we should briefly discuss the great sweet potato vs yam debate, which has been raging ever since potatoes were first brought to Europe. Yams are tubers from the genus Dioscorea, and they are native to Africa. Sweet potatoes are in the genus Ipomoea, and they are native to the New World. They are also not related to potatoes, which are in a separate plant genus, Solanum.
Confused yet? The issue with yams, sweet potatoes, and potatoes began when sweet potatoes were first brought to Europe, and called potatoes. When true potatoes entered Europe, Europeans realized that they were entirely different plants, and they created a retronym, “sweet potato” to describe the plants they previously called potatoes. The trend of referring to some sweet potatoes as “yams” emerged in the American South, where growers started referring to soft-fleshed sweet potatoes as yams to differentiate them from the firmer, less sweet varieties grown in the North.
Now that we've dealt with that problem, let's talk about Okinawan sweet potatoes, which made their way to China from the New World at some point between 1492 and 1605, when they were first brought over to Japan. The Japanese realized that this tuber could make a very useful crop, as it is extremely hardy and well equipped to deal with the sometimes mercurial weather in Japan. The Okinawan sweet potato quickly entered popular Japanese cuisine, where it is used in tempura, mashed and served with a variety of foods, and even integrated into pastries. You may see them called tamai kuru or beni imo in Japan.
Like many other aspects of Japanese cuisine, Okinawan sweet potatoes came to Hawaii, where they are a cornerstone of Hawaiian cuisine. Food historians claim that this is not because of the astounding purple color, but rather because these tubers are flavorful, creamy, and high in fiber, vitamin C, and antioxidants. From Hawaii, they have entered the mainland United States, where they are primarily consumed as a novelty food, especially in the case of sweet potato pie, which looks quite lurid when prepared with Okinawan sweet potatoes.