Invasive Plants of Washington

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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 Name Common Name Lifeform Habitat
Ailanthus altissima Tree-of-heaven T U
Alliaria petiolata Garlic Mustard H U
Berberis thunbergii Japanese Barberry S U
Cardamine impatiens No common name H U
Celastrus orbiculatus Asiatic Bittersweet V U
Centaurea maculosa
(also called Centaurea biebersteinii)
Spotted Knapweed H O
Cynancum louiseae Black Swallowort H,V U
Elaeagnus umbellata Autumn Olive S O
Euonymus alatus Burning Bush S U
Fallopia japonica
(also called Polygonum cuspidatum)
Japanese Knotweed H U,W
Frangula alnus
(also called Rhamnus frangula)
European Buckthorn S U
Hesperis matronalis Dame's Rocket H U
Iris pseudacorus Yellow Iris H U
Lonicera x bella Bella Honeysuckle S U,W
Lonicera japonica Japanese Honeysuckle V U,W
Lonicera morrowii Morrow's Honeysuckle S U,W
Lythrum salicaria Purple Loosestrife H W
Microstegium vimineum Japanese Stiltgrass G U
Myosotis scorpiodes Forget-me-not H W
Nasturtium officinale (1) Watercress H W
Phragmites australis Common Reed G U,W
Rhamnus cathartica Buckthorn S U
Robinia pseudoacacia Black Locust T U
Rosa multiflora Multiflora Rose S U

Restricted and Invasive

Scientific Name Common Name Lifeform Habitat
Lonicera maakii (2) Amur Honeysuckle S U
Tussilago farfara Coltsfoot H U,W

Potentially Invasive

Scientific Name Common Name Lifeform Habitat
Acer ginnala Amur Maple T U
Acer pseudoplatanus Sycamore Maple T U
Aegopodium podagraria Goutweed H W
Datura stramonium Jimson-weed H C
Elaeagnus angustifolia Russian Olive S U
Elsholtzia ciliata Elsholtzia H U
Fallopia sachalinensis (3) Giant Knotweed H U
Glechoma hederacea Gill-over-the-ground H W
Ligustrum (4) Privet S U
Lychnis flos-cuculi Ragged Robin H O
Lysimachia nummularia Money H W
Phalaris arudinacea Reed Canary Grass G W
Poa compressa Canada Bluegrass G W
Polygonum caespitosum No common name H U
Rumex acetosella Sheep Sorrel H U
Solanum dulcamara Climbing Nightshade H,V U,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