Invasive non-native problem plants
Invasive plants are non-native plants which are well suited to their new environment. They grow particularly well and become "invasive", invading places where they are not welcome, becoming a pest, and strangling other plant and animal life.
As well as being non-native, invasive plants are usually fast growing (eg. fast growing shrubs planted to form hedges, or creeping plants), and lack local predators/consumers. They are often generalists that prosper in a wide range of conditions, although they may be more specialist and happen to suit the local conditions very well.
Most States have lists of invasive and 'obnoxious' plants. All responsible gardeners should refrain from planting these plants. Unfortunately many nurseries and big-box stores will continue to sell known invasive problem plants - so always do your own independent research.
Animals can also be invasive although introductions are more likely to be accidental. Notable exceptions are European House Sparrows and Starlings which were deliberately introduced into the US by a 'lover of Shakespeare'. Most of the introduced bird species died out, but these two generalist species have adapted and are now pests across much of North and Central America.
This tag will be used primarily for invasive plants, but can also be used for invasive animals.