Cambridge Secondary (7-9). Stage 8. Science. Learner's Book - Unit 4: Ecosystems - Question 28

Buffelgrass is native to Africa, Asia and the Middle East. It was planted in Arizona in the 1930s, as food for cattle. Now, it is spreading rapidly through the Sonoran Desert.
What is the name for a plant, such as buffelgrass, that is growing in an ecosystem where it does not belong?