Invasive Plants

A common misconception is that Alaska is largely free of invasive species. In fact, more than 340 invasive plant species have been reported in Alaska. These plants vary in their level of invasiveness, which is quantified using the invasive plant ranking system. The rankings, scaled from 0 to 100, are based on species' ecological impacts, biological attributes, distributions, and responses to control measures; higher rankings correspond to greater potential harm to natural ecosystems in Alaska. The University of Alaska Anchorage Center for Conservation Science maintains the Non-native Plant Species List for Alaska, with valuable summary information on 410 invasive plants that have or may become established, invasiveness ranking scores, and links to species' biographies. In the table below, we include 30 plants with the highest invasiveness scores. The ranking system and species' biographies were developed in collaboration with the USDA-FS and the Cooperative Extension Service.

See our Invasive Plant Publications page for more resources related to invasive plant management in Alaska, the Cooperative Extension Service Invasive Plant Partnership page, and the homepage for the UAA Center for Conservation Science.

The new Alaska Invasive Species Partnership logo.

Links & Resources

Non-Native Plant Species List – Alaska Center for Conservation Science

* visit the ACCS page to access the full list

Common Name	Scientific Name	Species Biography	Rank	Family	Est.	Occurrence
Eurasian watermilfoil	Myriophyllum spicatum L.	b i o.	90	Halagoraceae		Alaska Watchlist
Japanese knotweed	Fallopia japonica (Houtt.) Ronse Decr.	bio.	87	Polygonaceae	1981	Alaska
giant knotweed	Fallopia sachalinensis (F. Schmidt ex Maxim.) Ronse Decr.	bio.	87	Polygonaceae	2006	Alaska
Bohemian knotweed	Fallopia ×bohemica (J. Chrtek & Chrtkov) J.P. Bailey	bio.	87	Polygonaceae	2004	Alaska
spotted knapweed	Centaurea stoebe L.	bio.	86	Asteraceae	2004	Alaska
smooth cordgrass	Spartina alterniflora Loisel.	bio.	86	Poaceae		Alaska Watchlist
common cordgrass	Spartina anglica C.E. Hubbard	bio.	86	Poaceae		Adjacent Canada only
denseflower cordgrass	Spartina densiflora Brongn.	bio.	86	Poaceae		Adjacent Canada only
saltmeadow cordgrass	Spartina patens (Aiton) Muhl.	bio.	86	Poaceae		Adjacent Canada only
leafy spurge	Euphorbia esula L.	---	84	Euphorbiaceae	2012	Alaska
purple loosestrife	Lythrum salicaria L.	bio.	84	Lythraceae	2006	Alaska
European wand loosestrife	Lythrum virgatum L.	bio.	84	Lythraceae		Alaska Watchlist
reed canarygrass	Phalaris arundinacea L. (cultivar)	bio.	83	Poaceae	1905	Alaska
common reed	Phragmites australis (Cav.) Trin. ex Steud.	bio.	83	Poaceae		Adjacent Canada only
ornamental jewelweed	Impatiens glandulifera Royle	bio.	82	Balsaminaceae	2004	Alaska
giant hogweed	Heracleum mantegazzianum Sommier & Levier	bio.	81	Apiaceae	2010	Alaska
white sweetclover	Melilotus albus Medik.	bio.	81	Fabaceae	1913	Alaska
waterthyme	Hydrilla verticillata (L. f.) Royle	bio.	80	Hydrocharitaceae		Alaska Watchlist
American white waterlily	Nymphaea odorata Aiton ssp. odorata	bio.	80	Nymphaeaceae	1997	Alaska
Himalayan knotweed	Persicaria wallichii Greuter & Burdet, Willd.	bio.	80	Polygonaceae	2006	Alaska
Canadian waterweed	Elodea canadensis Michx.	bio.	79	Hydrocharitaceae	1982	Alaska
western waterweed	Elodea nuttallii (Planch.) H. St. John	bio.	79	Hydrocharitaceae	1982	Alaska
orange hawkweed	Hieracium aurantiacum L.	bio.	79	Asteraceae	1969	Alaska
meadow hawkweed	Hieracium caespitosum Dumort.	bio.	79	Asteraceae	2004	Alaska
cheatgrass	Bromus tectorum L.	bio.	78	Poaceae	1923	Alaska
Himalayan blackberry	Rubus discolor Weihe & Nees	bio.	77	Rosaceae	2006	Alaska
Canada thistle	Cirsium arvense (L.) Scop.	bio.	76	Asteraceae	1925	Alaska
Siberian peashrub	Caragana arborescens Lam.	bio.	74	Fabaceae	1995	Alaska
European bird cherry	Prunus padus L.	bio.	74	Rosaceae	1980	Alaska
chokecherry	Prunus virginiana L.	bio.	74	Rosaceae	2009	Alaska

Contact Invasive Species Coordinator Joni Johnson at joni.m.johnson@usda.gov.

https://www.fs.usda.gov/detailfull/r10/forest-grasslandhealth/?cid=FSEPRD695230