American Bistort, Snakeweed, Mountain Meadow Knotweed, Western Bistort: Bistorta bistortoides (Synonyms: Persicaria bistortoides, Polygonum bistortoides, Polygonum bistortoides var. linearifolium, Polygonum bistortoides var. oblongifolium, Polygonum cephalophorum, Polygonum glastifolium, Polygonum vulcanicum) -
Alpine Bistort, Serpent-grass, Viviparous Bistort: Bistorta vivipara (Synonyms: Persicaria vivipara, Polygonum viviparum, Polygonum viviparum var. macounii) -
Bohemian Knotweed, Hybrid Knotweed: Fallopia xbohemica (Synonyms: Polygonum xbohemicum, Reynoutria xbohemica) -
Black Bindwed, Climbing Bindweed, Climbing Knotweed, Cornbind, Ivy Bindweed: Fallopia convolvulus (Synonyms: Bilderdykia convolvulus, Fallopia convolvulus var. subulata, Polygonum convolvulus, Polygonum convolvulus var. convolvulus, Reynoutria convolvulus, Tinaria convolvulus) -
Japanese Knotweed: Fallopia japonica var. japonica (Synonym: Polygonum cuspidatum) -
Giant Knotweed: Fallopia sachalinensis (Synonym: Polygonum sachalinense) -
Davis' Knotweed, Newberry's Fleeceflower, Newberry's Knotweed: Koenigia davisiae var. davisiae (Synonyms: Aconogonon davisiae, Aconogonon davisiae var. davisiae, Aconogonum davisiae, Aconogonum davisiae var. glabrum, Polygonum davisiae, Polygonum newberryi, Polygonum newberryi var. glabrum, Polygonum newberryi var. newberryi) -
Alpine Knotweed, Jimson Knotweed, Pokeweed Fleeceflower, Poke Knotweed: Koenigia phytolaccifolia (Synonyms: Aconogonum phytolaccifolium, Aconogonon phytolaccifolium var. glabrum, Aconogonon phytolaccifolium var. phytolaccifolium, Polygonum phytolaccaefolium, Polygonum phytolaccifolium) -
Water Smartweed, Water Knotweed: Persicaria amphibia (Synonyms: Polygonum amphibium, Polygonum amphibium var. coccineum, Polygonum amphibium var. emersum, Polygonum amphibium var. natans, Polygonum amphibium var. stipulaceum, Polygonum coccineum, Polygonum coccineum var. coccineum, Polygonum coccineum var. hartwrightii, Polygonum natans) -
Smartweed, Marshpepper Smartweed, Mild Water-pepper: Persicaria hydropiper (Synonyms: Polygonum hydropiper, Polygonum hydropiper var. projectum) -
Swamp Smartweed, Waterpepper, Water Pepper: Persicaria hydropiperoides (Synonyms: Persicaria opelousana, Persicaria paluldicola, Polygonum hydropiperoides, Polygonum hydropiperoides var. asperifolium, Polygonum hydropiperoides var. breviciliatum, Polygonum hydropiperoides var. buschianum, Polygonum hydropiperoides var. digitatum, Polygonum hydropiperoides var. hydropiperoides, Polygonum hydropiperoides var. opelousanum, Polygonum hydropiperoides var. psilotachyum, Polygonum opelousanum, Polygonum opelousnum var. adenocalyx, Polygonum persicarioides) -
Curltop Ladysthumb, Curlytop Knotweed, Dock-leaf Smartweed, Pale Smartweed, Willow Weed: Persicaria lapathifolia (Synonyms: Polygonum incanum, Polygonum incarnatum, Polygonum lapathifolilum, Polygonum lapathifolium var. lapathifolium, Polygonum lapathifolium var. salicifolium, Polygonum linicola, Polygonum nodosum, Polygonum scabrum, Polygonum tomentosum) -
Heartweed, Lady's-thumb, Redshank, Spotted Ladysthumb: Persicaria maculosa (Synonym: Polygonum persicaria) -
Pinkweed: Persicaria pensylvanica (Synonym: Polygonum pensylvanicum) -
Dotted Knotweed, Dotted Smartweed, Water Smartweed: Persicaria punctata (Synonyms: Polygonum acre, Polygonum acre var. leptostachyum, Polygonum punctatum, Polygonum punctatum var. confertiflorum, Polygonum punctatum var. ellipticum, Polygonum punctatum var punctatum) -
Himalayan Knotweed: Persicaria wallichii (Synonym: Persicaria wallichii var. wallichii, Polygonum polystachyum) -
Blake's Knotweed, Leathery Knotweed: Polygonum achoreum (Synonym: Polygonum erectum ssp. achoreum) -
Austin's Knotweed: Polygonum austiniae (Synonyms: Polygonum douglasii ssp. austiniae, Polygonum douglasii var. austiniae) - Threatened in Washington.
American Knotweed, Prairie Knotweed, Renouee Faux-buis: Polygonum aviculare ssp. buxiforme (Synonyms: Polygonum aviculare var. littorale, Polygonum buxiforme, Polygonum littorale) -
Common Knotweed, Oval-leaf Knotweed: Polygonum aviculare ssp. depressum (Synonyms: Polygonum aequale, Polygonum arenastrum, Polygonum aviculare ssp. aequale, Polygonum aviculare ssp. calculatum, Polygonum aviculare ssp. microspermum, Polygonum aviculare var. depressum, Polygonum calcatum, Polygonum microspermum, Polygonum montereyense) -
Narrow-lef Knotweed: Polygonum aviculare ssp. neglectum (Synonyms: Polygonum aequale ssp. oedocarpum, Polygonum aviculare var. angustissimum, Polygonum aviculare ssp. rectum, Polygonum neglectum) -
California Knotweed: Polygonum californicum -
Cascade Knotweed, Cascades Polygonum: Polgonum cascadense -
Douglas Knotweed, Douglas' Knotweed, Douglas's Knotweed, Austin's Knotweed: Polygonum douglasii (Synonyms: Polygonum douglasii ssp. douglasii, Polygonum douglasii var. douglasii, Polygonum douglasii var. latifolium, Polygonum emaciatum) -
Erect Knotweed: Polygonum erectum (Synonym: Polygonum aviculare var. erectum) -
Wiry Knotweed, Palouse Knotweed: Polygonum majus (Synonyms: Polygonum coarctatum, Polygonum douglasii ssp. majus) -
Broad-leaved Knotweed, Broadleaf Knotweed, Leafy Dwarf Knotweed, Redstem Knotweed, Zigzag Knotweed: Polygonum minimum (Synonym: Polygonum torreyi) -
Nuttall's Knotweed: Polygonum nuttallii (Synonyms: Polygonum douglasii ssp. nuttallii, Polygonum intermedium) -
Parry's Knotweed: Polygonum parryi -
Closeflowered Knotweed, Close-flowered Knotweed: Polygonum polygaloides ssp. confertiflorum (Synonyms: Polygonum confertiflorum, Polygonum kelloggii var. confertiflorum, Polygonum watsonii) -
Kellogg's Knotweed, White-margined Knotweed : Polygonum polygaloides ssp. kelloggii (Synonyms: Polygonum kelloggii, Polygonum minutissimum, Polygonum unifolium) -
Pokeweed Fleeceflower, Polygala Knotweed: Polygonum polygaloides ssp. polygaloides (Synonym: Polygonum polygaloides var. montanum) -
Sawatch Knotweed: Polygonum sawatchense ssp. oblivium - Rare in Washington.
Sawatch Knotweed: Polygonum swatchense ssp. sawatchense (Synonyms: Polygonum douglasii ssp. johnstonii, Polygonum douglasii var. johnstonii, Polygonum exile, Polygonum triandrum) -
Shasta Knotweed: Polygonum shastense -
Fall Knotweed, Spurry Knotweed: Polygonum spergulariaeforme (Synonyms: Polygonum douglasii ssp. spergulariiforme, Polygonum spergulariaeforme) -