Invasive Plants of Washington

This is a list of the non-native invasive plants that are present in Washington. It was derived from Non-native Invasive and Potentially Invasive Vascular Plants in Connecticut by Mehrhoff, L.J., K.J. Metzler and E.E. Corrigan (available as a PDF download from the Connecticut Invasive Plant Working Group website).

What makes a plant invasive? Refer to criteria here.

Please note that the terms Widespread and Invasive, Restricted and Invasive, and Potentially Invasive refer to plant status in Connecticut; status of certain plants in Washington, if different, is noted. For definitions of terms, please refer to the above website.

Widespread and Invasive

Scientific NameCommon NameLifeformHabitat
Ailanthus altissimaTree-of-heavenTU
Alliaria petiolataGarlic MustardHU
Berberis thunbergiiJapanese BarberrySU
Cardamine impatiensNo common nameHU
Celastrus orbiculatusAsiatic BittersweetVU
Centaurea maculosa
(also called Centaurea biebersteinii)
Spotted KnapweedHO
Cynancum louiseaeBlack SwallowortH,VU
Elaeagnus umbellataAutumn OliveSO
Euonymus alatusBurning BushSU
Fallopia japonica
(also called Polygonum cuspidatum)
Japanese KnotweedHU,W
Frangula alnus
(also called Rhamnus frangula)
European BuckthornSU
Hesperis matronalisDame's RocketHU
Iris pseudacorusYellow IrisHU
Lonicera x bellaBella HoneysuckleSU,W
Lonicera japonicaJapanese HoneysuckleVU,W
Lonicera morrowiiMorrow's HoneysuckleSU,W
Lythrum salicariaPurple LoosestrifeHW
Microstegium vimineumJapanese StiltgrassGU
Myosotis scorpiodesForget-me-notHW
Nasturtium officinale (1)WatercressHW
Phragmites australisCommon ReedGU,W
Rhamnus catharticaBuckthornSU
Robinia pseudoacaciaBlack LocustTU
Rosa multifloraMultiflora RoseSU

Restricted and Invasive

Scientific NameCommon NameLifeformHabitat
Lonicera maakii (2)Amur HoneysuckleSU
Tussilago farfaraColtsfootHU,W

Potentially Invasive

Scientific NameCommon NameLifeformHabitat
Acer ginnalaAmur MapleTU
Acer pseudoplatanusSycamore MapleTU
Aegopodium podagrariaGoutweedHW
Datura stramoniumJimson-weedHC
Elaeagnus angustifoliaRussian OliveSU
Elsholtzia ciliataElsholtziaHU
Fallopia sachalinensis (3)Giant KnotweedHU
Glechoma hederaceaGill-over-the-groundHW
Ligustrum (4)PrivetSU
Lychnis flos-cuculiRagged RobinHO
Lysimachia nummulariaMoneyHW
Phalaris arudinaceaReed Canary GrassGW
Poa compressaCanada BluegrassGW
Polygonum caespitosumNo common nameHU
Rumex acetosellaSheep SorrelHU
Solanum dulcamaraClimbing NightshadeH,VU,W



  • T = tree
  • H = herbaceous plant
  • S = shrub
  • G = grass
  • V = vine
  • A = aquatic


  • U = uplands (all upland habitats including closed-canopy forests, second-growth woods, fields, grasslands, ridge tops, sand barrens, pitch pine scrub lands, etc.)
  • O = open areas (fields, grasslands, sand barrens, dry meadows, etc.)
  • W = wetlands (swamps, marshes, wet meadows fens, bogs, flood plains, flood plain forests, pond and stream shores)
  • L = lakes (ponds, impounded water)
  • R = rivers (streams, in running water)
  • C = coast (sand dunes, rocky headlands, upper edges of salt water tidal marshes)


1,3 Restricted and Invasive in Washington
2 Widespread and Invasive in Washington
4 Species present in Washington not yet determined

Please note that Giant Hogweed (Heracleum mantegazzianum) is not included in the above list as it has not yet been observed growing outside of cultivation in Washington (refer to criteria here).

Compiled and edited by E. Corrigan, 
Conservation Commission 
Co-chair Connecticut Invasive Plant Working Group 
December, 2004