The Ancient Dispersal Of Useful Plants
George F. Carter, a noted geographer, summarizes the botanical evidence for early transoceanic voyages.
Domestic cotton. Thousands of years old in the Americas; believed to be a hybrid between New World wild cotton and species from southwest Africa.
Bottle gourds. Of African origin but known in Peru about 11,000 years ago; dispersible by ocean currents but appeared in Peru only after humans learned how to navigate on the oceans.
Sweet potatoes. A New World plant that has been known in Polynesia for at least 500 years; but the South American name for the sweet potato (kumara) turns out to be a Sanskrit word from India, which is most perplexing.
Coconuts. Arrived in the Americas from the Indian Ocean region via Polynesia; can be dispersed by ocean currents, but this long eastward voyage would have been counter to many currents.
Peanuts. Well-established on the Peruvian coast thousands of years ago, but the same variety was known in preShang China before 1500 BC.
(Carter, George F.; "Kilmer's Law: Plant Evidence of Early Voyages," Oceans, 12:8, 1979.)
Reference. Our Handbook Ancient Man contains much more evidence for Precolumbian contacts with the New World. Information on this large volume is located at: here.