A plant is considered native if it has occurred naturally in a particular region, ecosystem, or habitat without human introduction. Exotic plants that evolved in other parts of the world or were cultivated by humans into forms that don't exist in nature do not support wildlife as well as native plants.
Native plants help the environment the most when planted in places that match their growing requirements. They will thrive in the soils, moisture and weather of your region. That means less supplemental watering, which can be wasteful, and pest problems that require toxic chemicals. Native plants also assist in managing rain water runoff and maintain healthy soil as their root systems are deep and keep soil from being compacted.