A species whether it is plants, diseases, fungi, parasites, feral animals, introduced marine pests, insects and other invertebrates can be defined as invasive when it is found beyond its accepted normal distribution range and which threatens valued environmental, agricultural or other social resources by the damage it causes.
Invasive species have a major impact on the environment, threatening the unique biodiversity and reducing overall species abundance and diversity. Different countries have their own list of what is considered to be invasive species.
BBC Earth News reports that non-native garden plants pose a threat to the countryside including National Parks. Invasive plants compete with native plants for light, space and nutrients. In addition, non-native plants do not tend to produce food appealing to native animals, reducing the space for local wildlife.