[Wikipedia] Invasiveness & distribution: The plant is most invasive in wetland habitats, including riparian zones; from there it easily spreads to other ecosystems, such as sagebrush.[3] It is perceived as a threat to salt marshes in southern New Hampshire, United States, prompting the Department of Environmental Services and the U.S. Fish and Wildlife Service to look for it in the Hampton?Seabrook Estuary in 2008, where it is thought to have spread. The agencies were recruiting volunteers to help look for and properly remove it from this area.[4] It is also a pest in the Monte Vista and Alamosa National Wildlife Refuges in Colorado and Malheur National Wildlife Refuge in Oregon, and many other sites. This plant is native to southern Europe, Mediterranean countries and Asia as far east as the Himalayas. It is an introduced species in North America, where it grows throughout the United States and Mexico, and Australia. It may have been introduced to the United States when its seed got into a shipment of sugar beet seeds. (contributed by Mary Ann Machi)