How would America look different if there had been no Columbian exchange?
America would look tremendously different without the Columbian Exchange. There would be huge differences in the people, the plants, and the animals.
In terms of human populations, there would be many more Native Americans. A major aspect of the Columbian Exchange was the germs that the Europeans brought. These germs wiped out the vast majority of Native Americans.
In terms of flora and fauna, things would be much different as well. There would be no wheat in North America. There would be no citrus growing in California and Florida. There would not even be dandelions. There would be no large domesticated animals. There would be no cattle, no horses, no sheep and no pigs.
In all these ways, America would look very different without the Columbian Exchange.