The seeds are carried by birds and can survive in a dormant state for years.
Lots of stuff like trees washed away by rivers end up floating in the ocean.
But it's also perfectly feasible that a limited trade happened far in the past.
Polynesians showed that you can reliably cross even the pacific on boats made using stone tools and fire.

[–] ZombiFrancis@sh.itjust.works 1 points 2 weeks ago (1 children)

Humans before the Ice Age were fishing for tuna in the deep sea and were coastal hopping everywhere there are coasts to hop.

[–] baldingpudenda@lemmy.world 1 points 2 weeks ago

Most of human history:

[–] theneverfox@pawb.social 1 points 2 weeks ago

Limited trade... There were full on global trade networks through most of human history. Ironically, not as much across the Atlantic, because civilization in the Americas was centered on the West coast

But you find all sorts of stuff turning up everywhere. Not much of it, and most of it is lost to history, but enough to establish that global trade networks were the norm and not the exception