This pure Vitamin C is ascorbic acid in unbuffered form, and may be preferred by sensitive individuals who tolerate its mild acidity. Cassava, or Manihot esculenta, is a bushy South American shrub with long tuberous roots, which are traditionally eaten like potatoes. Cassava root starch serves as the starting material for a multi-step chemical process of manufacturing ascorbic acid. It is well tolerated by individuals unable to tolerate other sources of vitamin C.