U.S. DEPARTMENT OF THE INTERIORBUREAU OF LAND MANAGEMENT
Noxious Weed Definitions
California Food and Agriculture Code: "Any species of plant which is, or is liable to be, detrimental or destructive and difficult to control or eradicate, which the director, by regulation, designates to be a noxious weed."
Bureau of Land Management Partners Against Weeds Action Plan: "A plant that interferes with management objectives for a given area of land at a given point in time."
U.S. Forest Service: "Those plant species designated as noxious by the Secretary of Agriculture or by the responsible State official. Noxious weeds generally possess one or more of the following characteristics: aggressive and difficult to manage, poisonous, toxic, parasitic, a carrier or host of serious insects or disease and being native or new to or not common to the United States or parts thereof."
Undesirable Plant Species
Federal Noxious Weed Act of 1974, as amended: "Plant species that are classified as undesirable, noxious, harmful, exotic, injurious, or poisonous, pursuant to State or Federal law. Species listed as endangered by the Endangered Species Act of 1973 shall not be designated as undesirable plants under this section and shall not include plants indigenous to an area
Weed Science Society of America: "A plant growing where it is not desired."
Bazzaz, F.A. 1986. Life History of Colonizing Plants: "Species that are introduced intentionally or unintentionally into ecosystems where they have never been before, and cause changes in the structure and function of these ecosystems. Such species often spread relatively quickly. They may modify the resident community, and in some cases may usurp much of the resources of the habitat."
Western Society of Weed Science, Weeds of the West: "A plant that interferes with management objectives for a given area
Webster's: "A plant that is not valued where it is growing and is usually of rank growth, especially one that tends to overgrow or choke out more desirable plants."
USDA Animal & Plant Health Protection Service: "Recognized harmful non-indigenous species that pose a threat to agricultural and managed ecosystems, or threaten the biodiversity of natural ecosystems."