The oldest known archaeological race of maize is a pod-popcorn . The closest living wild relative of cultivated maize is teosinte . Although the morphological differences between maize and teosinte are spectacular in appearance they are conspecific genetically . The tripartite hypotheses proposes that the ancestor of domesticated maize was a now extinct wild pod-popcorn ; that teosinte originated from maize-Tripsacum hybridization ; and that introgression with either teosinte or Tripsacum gave rise to the tripsacoid syndrome characteristic of many modern races of maize . Maize and teosinte cross readily, and exchange genes wherever they are sympatric . Hybrids between maize and Tripsacum are not always easy to produce, but natural introgression between these taxa is possible . However, artificially induced introgression from Tripsacum into maize failed to produce either teosinte-like offspring or the combination of tripsacoid characteristics assumed to indicate such introgression during the evolution of several South American races of maize . The available archaeological data seem to exclude teosinte as a possible ancestor of domesticated maize . This will make maize the only cereal without a living direct ancestor . Biosystematic studies suggest that teosinte is so closely related to domesticated maize that it could be accepted as the progenitor of maize .