North Carolina designated the sweet potato (Ipomoea batatas) as the official state vegetable in 1995. Native Americans were growing sweet potatos in North Carolina long before European colonization.

Sweet potato fries - photo by Angela Boyko on Flickr -
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North Carolina is the largest producer of sweet potatos in the U.S., harvesting over four billion pounds of the vegetable in 1989. The sweet potato is high in vitamins A and C and low in fat.
There are about 50 genera and more than 1000 species of this family, but only Ipomoea batatas is a crop plant (grown as an important root vegetable). The genus Ipomoea also includes several garden flowers called morning glories (the blossom of the sweet potato looks very much like a morning glory):

Sweet potato plant in bloom - photo by Danielm on Wikipedia - published under terms of the GNU Free Documentation License Version 1.2 or later
The large, starchy, sweet-tasting tuberous roots of the sweet potato can be prepared in a variety of ways including baked, french-fried, and candied. The young leaves and shoots are sometimes eaten as greens.
The sweet potato is only distantly related to the potato (Solanum tuberosum). Sweet potatos are often called yams in parts of North America, although they are only very distantly related to the other plant that is widely known as yams (in the Dioscoreaceae family) which is native to Africa and Asia.