<P> Plants that arrived by land, sea, or air in the times before 1492 are called archaeophytes, and plants introduced to Europe after those times are called neophytes . Invasive species of plants and pathogens also were introduced by chance, including such weeds as tumbleweeds (Salsola spp .) and wild oats (Avena fatua). Some plants introduced intentionally, such as the kudzu vine introduced in 1894 from Japan to the United States to help control soil erosion, have since been found to be invasive pests in the new environment . </P> <P> Fungi have also been transported, such as the one responsible for Dutch elm disease, killing American elms in North American forests and cities, where many had been planted as street trees . Some of the invasive species have become serious ecosystem and economic problems after establishing in the New World environments . A beneficial, although probably unintentional, introduction is Saccharomyces eubayanus, the yeast responsible for lager beer now thought to have originated in Patagonia . </P> <P> In addition to these, many animals were introduced to new habitats on the other side of the world either accidentally or incidentally . These include such animals as brown rats, earthworms (apparently absent from parts of the pre-Columbian New World), and zebra mussels, which arrived on ships . Escaped and feral populations of non-indigenous animals have thrived in both the Old and New Worlds, often negatively impacting or displacing native species . In the New World, populations of feral European cats, pigs, horses and cattle are common, and Burmese pythons are considered problematic . In the Old World, Eastern gray squirrel have been particularly successful in colonising Great Britain and populations of raccoons can now be found in some regions of Germany, the Caucasus and Japan . Fur farm escapees such as coypu and American mink have extensive populations . Canada geese are also common . </P>

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