Wild forms not known with certainty. The sweet potato is a true root. Also reproduced vegetatively using portions of the aerial stem. They are used there to prepare starch, wine and alcohol. They are also widely fed to animals.
China is easily the worlds leading producer.
Widely eaten in the southern U.S. Not eaten particularly in Europe. Sweet potatoes Cassava or Manioc. It is the major starchy food for more than 500 million people. Griddles for cooking it go back at least 2000 years. However, since the crop developed in the lowland tropics where preservation is poor, it may go back much farther.