what allows the plant to be categorised as an alien plant.

Question: what allows the plant to be categorised as an alien plant.
- Keywords:
  alien plant,
  categorise
Asked by shaz to Zarah on 7 Nov 2016. This question was also asked by oj.
- Zarah Pattison answered on 7 Nov 2016:
  
  Hi there!
  
  Plants that are brought by humans to other countries (for eg bringing American plants to the UK) are called alien or non-native plants.
  
  An alien plant would not have been able to colonise the new habitats without the help of humans.
  
  Z

Question: what allows the plant to be categorised as an alien plant.