"there weren't a lot of opportunities for anyone to get American plants back to Europe prior to Columbus" Thinking about this myself a while ago, I wondered -

"there weren't a lot of opportunities for anyone to get American plants back to Europe prior to Columbus" Thinking about this myself a while ago, I wondered - even if someone went there and back, and even brought something along, how could we tell? That Norse saga had a mythical status at most, and even with that it isn't necessarily clear for a casual listener that it may be about reaching another previously unknown continent. Other groups along the history may have also pulled it off, but then their contemporaries, in order to consemnate the event, had to take their word for it? Even with some seeds as evidence, the world was less connected untill very recently and there were plenty of isolated places, yet relatively close, for strange seeds to be found. After thousand of years, it's hard to tell if an annual plant was brought at some point in time by intercontinental explorers, or migrated by some other non-human related way, or has been local since before continents went appart. Then it was hard to discern the magnitude of a discovery. Even the Norsemen, like the later Spaniard colonists, couldn't tell how big their found body of land was, if the Vinland they reached was an island they haven't yet circumnavigated yet or happened to be a continent spanning south down to well into southern hemisphere. No, for a discovery like this to stick, with clear compiled inventories of imported plants, it had to be done by a government-like entity, that could afford the high risks of loss that an exploration program on the limits of available technology pose, and with enough logistics and cultural development to pursue a wide range of interests (as opposed to small groups, for which keeping track of traffiked plants may be of lesser concern).