Washington State county boundaries from Washington Department of Natural Resources. Acres of distribution calculated from following maps published by the Washington State Department of Agriculture in 2011: Knotweed, Bohemian, “Polygonum bohemicum” Distribution 2011. Giant, “Polygonum sachalinense” Distribution 2011. Himalayan, “Polygonum polystachyum” Distribution 2011. Knotweed, Japanese, “Polygonum cuspidatum” Distribution 2011. PRISM projects extracted from PRISM website Project Search @ https://secure.rco.wa.gov/PRISM/search/ProjectSearch.aspx in 2015.