An additional factor that slowed the spread of crops in the Americas was that the two major crops that were domesticated have their origins in highland species.
Zea mays was the only one of the two that spread widely and even that took a long time. It's domestication was a fortunate chance arising from a single hybridization of two teosinte species around 7,000 B.C. somewhere in the Balsas river valley in Mexico. It took another millenia or so for varietals capable of growing in tropical lowlands to arise and spread as far as Central America. In South America there were two waves of maize entry, first a higland wave 4000 B.C. and a later tropical lowland one around around 2000 years ago.
As for Solanum tuberosum (Potatoes) it's domestication in the Andes predates that of Maize by at least a millenia. It did not spread beyond its highland home till the Spanish conquest of the Incas.
There were some later abortive domestications of grains in eastern North America which were abandoned with the arrival of Maize. A possible point of divergence would be an earlier domestication of these or their not being abandoned as was the case with knotweed (Polygonum erectum), little Barley (Hordeum pusillum) and Maygrass (Phalaris caroliliana).
There is evidence of a potatoe relative (Solanum jamesii) in western North America being consumed as early 10,900 years ago. It may have been domesticated but not to the degree of it's South American cousin.
Zea mays was the only one of the two that spread widely and even that took a long time. It's domestication was a fortunate chance arising from a single hybridization of two teosinte species around 7,000 B.C. somewhere in the Balsas river valley in Mexico. It took another millenia or so for varietals capable of growing in tropical lowlands to arise and spread as far as Central America. In South America there were two waves of maize entry, first a higland wave 4000 B.C. and a later tropical lowland one around around 2000 years ago.
As for Solanum tuberosum (Potatoes) it's domestication in the Andes predates that of Maize by at least a millenia. It did not spread beyond its highland home till the Spanish conquest of the Incas.
There were some later abortive domestications of grains in eastern North America which were abandoned with the arrival of Maize. A possible point of divergence would be an earlier domestication of these or their not being abandoned as was the case with knotweed (Polygonum erectum), little Barley (Hordeum pusillum) and Maygrass (Phalaris caroliliana).
There is evidence of a potatoe relative (Solanum jamesii) in western North America being consumed as early 10,900 years ago. It may have been domesticated but not to the degree of it's South American cousin.