Because the historical distributions of some species are unknown or unclear, research continues to attempt to unravel the tangle of human and natural influences responsible for their current ranges. Growth Habit - Invasiveness . The most important aspect of an alien plant is how it responds to a new environment. An invasive species is one that displays rapid growth and spread, allowing it to establish over large areas. Free from the vast and complex array of natural controls present in their native lands, including herbivores, parasites, and diseases, exotic plants may experience rapid and unrestricted growth in new environments.
Invasive plants reproduce rapidly, either vegetatively or by seed.
Their phenomenal growth allows them to overwhelm and displace existing vegetation and form dense one-species stands. Not all exotic species are considered harmful . However, each alien plant is one less native host plant for our native insects, vertebrates and other organisms that are dependent upon them. Weeds, Wildlands and Natural Areas . In other words, weeds can include native and non-native plants alike, growing wherever someone wishes they weren't.