• Some foreign plants have become invasive in the state of Oregon.Nathan Blaney/Photodisc/Getty Images
  
  When plants move from one country to another, they sometimes do not have the same natural predators and competition as they do back home. Without natural enemies to keep their growth in check, some plants from outside of Oregon have become invasive. They affect the state by taking over land once inhabited by native plants and changing the ecosystem in potentially harmful ways.
  
  

African Rue

• The Oregon Invasive Species Council lists African rue as one of the 100 most dangerous invaders to keep out of Oregon. According to the Oregon Department of Agriculture, this plant has shown up in Central Oregon counties of Harney and Crook. The plant originally comes from African and Asian deserts, and affects native Oregon plants by germinating earlier in the spring than them and taking over their growing space. African rue also produces toxins that can kill livestock if they eat the plant. It is a bushy succulent with white flowers from spring to early fall. The State of Oregon is currently trying to eliminate all African rue to protect cattle and native Oregonian plants.
  
  

Giant Hogweed

• Giant hogweed is another plant on the Oregon Invasive Species Council's 100 most dangerous invaders list. It reaches 10 to 15 feet tall and has 3- to 5-feet wide leaves. Giant hogweed originally comes from Asia. It negatively impacts Oregon because of its invasive nature, which displaces native plants. According to the Oregon Department of Agriculture, it also poses a serious health risk to humans, because its sap makes the skin hypersensitive to the sun's rays and leads to severe burns. People originally brought the plant to North America to grow in gardens and arboretums, but it eventually escaped into the wild. In Oregon, the plant mostly grows in the Northwestern part of the state, where environmentalists are trying to eradicate the plant.
  
  

English Ivy

• English ivy easily grows up vertical surfaces.Ivy image by Tomasz Pawlowski from Fotolia.com
  
  English ivy spreads rapidly, covering the ground and growing up vertical surfaces. This plant originally came from Asia and Europe, according to the National Park Service. Oregon has had problems with the ivy spreading out of the areas where gardeners planted it and subsequently harming trees and other plants. Ivy can cover the foliage on tree branches, causing the branches to die. It also makes them heavier and more prone to damage during storms. When gardeners physically remove the ivy, it often grows back. It creates an ideal habitat for bacterial diseases that can infect other nearby plants. English ivy also causes health problems in humans if ingested.