DaisyI said:If they are pretty, who cares? I personally love pretty, invasive plants. My yard is being taken over by blue flax. I don't care. 
I care because I live in a state that has major problems with non-native invasive plants (both terrestrial and aquatic) which cause damage to the environment and can wreak havoc and destroy naturally balanced native communities. The wildlife dependent on the native plants in their area are unable to adapt to the non-native invasive plants which causes die out of the wildlife of that region.
We have major issues here in the state of Florida where introduced species of plants and animals not native to the area have multiplied and gotten out of hand. The invasive plants choke out and completely kill native plants to the area and the non-native introduced animals do the same. We have everything from invasive fish to birds to snakes and frogs that have gotten out of hand in this state.
Some non-natives are not of real concern but others are really noxious:
http://www.usna.usda.gov/Garde...
