After spending some time in the New World, native plants were discovered that could serve the same purposes as the ones brought over from Europe. The transplanted species, however, thrived in America, escaping over fences and walls, venturing into the wide-open spaces of the New World. They were then considered to be weeds. Weed species generally grow very rapidly after germination from seed, and this gives them an immediate advantage. Weeds are also very vigorous.
Some weeds have special dispersal mechanisms, which contributes to their success.
Weeds and crops share many characteristics, which makes it likely that they would be found near each other. Weeds and crops both rely on human intervention for establishment and weeds thrive in disturbed habitats. Practices that tend to favor crops also tend to favor weeds, since they may be similarly adapted to the same habitat. Weeds impact the lives of humans by affecting the health, crops, and domesticated animals of the land. Weeds reduce crop yield by competing for resources and reducing food, feed, and fiber quality.