The theory of pre-Columbian contact across the South Pacific Ocean between South America and Polynesia has received support from several lines of evidence, although solid confirmation remains elusive. A diffusion by human agents has been put forward to explain the pre-Columbian presence in Oceania of several cultivated plant species native to South America, such as the bottle gourd ("Lagenaria siceraria") or sweet potato ("Ipomoea batatas"). Direct archaeological evidence for such pre-Columbian contacts and transport has not emerged. Similarities noted in names of edible roots in Maori and Ecuadorian languages ("kumari") and Melanesian and Chilean ("gaddu") have been inconclusive.