Sweet potato is a vine plant, although it is not the same as the edible sweet potato. The sweet potato tubers that are used for cooking and eating come from a different plant that is in the same family as the sweet potato vine. Sweet potato vines are primarily ornamental.
Sweet potato vines are bred more as an aesthetic complement to gardens rather than as a food source. They were developed for the beauty of their leaves rather than their roots or tubers. They sometimes also produce edible tubers, but those tubers are usually very bitter or lacking in taste. The young leaves of the vine, however, are harvested as a delicacy.