The sweet potato was officially designated the State Vegetable by the General Assembly of 1995. (Session Laws, 1995, c. 521 ).
Students at a Wilson County  school petitioned the North Carolina General Assembly for the establishment of the sweet potato (Ipomoea batatas) as the Official State Vegetable. Their assignment led to the creation of this state symbol. The sweet potato is high in vitamins A and C and low in fat and was grown in North Carolina before the European colonization of North America.
References and additional resources:
"Sweet potatoes." 2010. NC Department of Agriculture & Consumer Services. Online at http://www.ncagr.gov/markets/commodit/horticul/sweetpot/ 
North Carolina Sweet Potato Commission. Online at http://www.ncsweetpotatoes.com/ 
NASS QuickStats search page (Statistics from the USDA/National Agricultural Statistics Service)
Resources in Worldcat 
1 June 2007 | Case, Steven