The "origin" of a range plant is the area where it evolved. It is important to know the origin of a plant because it can affect the way that a plant responds to the environment.
Native plants are those that originated and evolved in North America.
Introduced plants were brought to North America from another continent. Several of these plants were intentionally introduced to rangeland because they have good forage value. Other plants were accidentally introduced to North America, usually as contaminants in crop seeds. Weedy introduced plants were accidentally introduced or brought in for their ornamental value but then "escaped" into rangelands.