[jaratec]

It is the other way around. The sweet potato is natively from America, but it made it to Polynesia, unclear how.

[billfruit]

Is it the same "Tombez Potato" writers of the 19th century report as being commonly grown and consumed in the Pacific Islands like Marquesas?

[throwaway2048]

The fact that the leading theory of anthropologists for a long time was vegetation rafts is laughable in the face of the distances Polynesian people regularly traveled, it speaks to the parochial nature of much of the field.

[scq]

Sweet potatoes found in Polynesia diverged from their ancestors in the Americas 100,000 years ago, long before the islands were colonized by humans.

https://www.nature.com/articles/d41586-018-04488-4

[nkoren]

Also, the fact that many Polynesian languages used nearly the same word for "sweet potato" as some South American languages (kuumala -- Polynesian vs. kumara/cumal -- Quechua) is kind of a clue, yes?

The fact that the "vegetation raft" theory persisted for more than a few seconds in the face of this knowledge always astonished me.

[eythian]

Not just nearly the same. It's literally kūmara in Māori.