This list is retained for historical interest only. Please refer to the list of Non-native Invasive and Potentially Invasive Vascular Plants in Connecticut maintained by the Connecticut Invasive Plant Working Group for current information.

Non-native Invasive Plant Species

Occurring in Connecticut

Revised Edition

Leslie J. Mehrhoff

George Safford Torrey Herbarium

October 1997


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This is a list of vascular plant species which are invasive into "natural areas". Many of the species on this list also occur in disturbed areas and have the potential of invading nearby natural habitats. Most species included in the Main List are not native to Connecticut. The list does not include many of the long established non-native species that have been used as ornamentals or as crops or forage plants and can dominate small or large tracts of anthropogenic landscapes such as lawns and abandoned agricultural lands.

A "natural area", as it is used here, is hard to define. I do not mean sites officially designated as natural areas. Rather, I mean sites where recent human impacts are either minimal or if humans have managed the site it has been done for conservation reasons. I include in my loose definition sites for rare or imperiled species, conservation lands managed to preserve biological diversity, small or large undisturbed parcels that, for the most part, are natural or have not recently been impacted by humans. Natural disturbance is frequently a component of the system. I do not mean agricultural lands, gardens, roadsides, or other human-controlled landscapes. I have not listed agricultural or garden weeds or other so-called noxious weeds.

Appendix 1 includes species which, although locally abundant and spreading, do not usually disperse far from the original site of intentional introduction. Appendix 2 includes species that are native to some part of Connecticut but have either extralimital occurrences that are probably anthropogenic or non-indigenous genotypes. Appendix 3 and Appendix 4 are Watch Lists. Appendix 3 includes taxa about which there are questions. Some species included in Appendix 3 are present in the State but, in spite of their aggressively invasive nature elsewhere, do not seem to be invasive here at this point in time. Others are widespread in Connecticut but appear not to be invasive into natural habitats. Appendix 4 includes invasive taxa that are not yet documented from Connecticut but are reported from nearby states. These can be anticipated in Connecticut.

Taxa are arranged alphabetically by family, and within a family by Genus and species. Annotations with each entry may include the area to which the taxon is thought to be native, comments on its distribution, abundance, and dispersal in Connecticut, and year of earliest Connecticut specimen. The number following the "G&C-" refers to the page in Gleason and Cronquist's 2d edition (Gleason, H.A. and A. Cronquist. 1991. Manual of the Vascular Plants of Northeastern United States and Adjacent Canada 2d edition. New York Botanical Garden, Bronx, NY) where a description of the taxon can be found. Dates of earliest record from Connecticut are based on herbarium specimens. * = native to Connecticut.

This list is meant to be dynamic. Species will be added, deleted, or moved based upon additional data and comments from reviewers. Records for all species included here are from herbarium specimens. Additional records and specimens should be sent to the George Safford Torrey Herbarium. Reports of species included in Appendix 3 that are aggressively invading undisturbed habitats are needed to improve the list. Likewise, reports are sought of species included in Appendix 1 aggressively invading natural habitats that are well removed from and discontinuous with the site of original intentional introduction. Occurrences of species from Appendix 4 should be reported immediately.

This list will be reissued semiannually, in October and April.


I want to thank the following people for their helpful comments: Margaret Ardwin, Joe Dowhan, Glenn Dryer, Donna Ellis, Elizabeth Farnsworth, Dick Goodwin, Joyce Hemingson, Don Les, Chris Mangels, Mark McDonnell, Noble Proctor, and other field botanists who have answered questions over many years or commented on previous iterations of this list. The final choices, good or bad, have been mine. No one else should be held accountable.

Summary of Main List and Appendices

Category Species
Main List 51
Appendix 1 12
Appendix 2 5
Appendix 3 38
Appendix 4 8
Total Species 114

Please send comments, questions, and specimens to:

Leslie J. Mehrhoff, Curator

George Safford Torrey Herbarium

Department of Ecology and Evolutionary Biology

Box U-42, 75 North Eagleville Road

University of Connecticut

Storrs, CT 06269-3042

telephone: 860-486-1889 fax: 860-486-6364


Main List


Froelichia gracilis (Hook.) Moq. Cottonweed
Southwestern U.S.; sporadic along major highways; 1973; G&C-109.


Aegopodium podagraria L. Goutweed
Eurasia; invasive along streams; commonly planted and escaping from cultivation; G&C-371.


Vincetoxicum nigrum (L.) Moench. Black Swallow-wort
Europe; widespread and and increasingly common; wind dispersed; 1901; G&C-399.
Vincetoxicum rossicum (Kleo.) Barb. Swallow-wort
Europe; overlooked until recently, this species is common along coast and sporadic inland; wind dispersed; 1881; not in G&C.


Centaurea maculosa Lam. Spotted Knapweed
Europe; widespread along roadsides and disturbed areas, potentially a problem in early succussional habitats; G&C-615.


Berberis thunbergiiDC. Japanese Barberry
Japan; widespread and common, can form large monotypic stands in forest understory; bird dispersed; G&C-64.


Paulownia tomentosa (Thunb.) Steudel Empress-tree
China; commonly planted near coast, especially around old ports, seedlings and saplings common, especially in coastal New London and Fairfield Counties; G&C-493.


Alliaria petiolata (Bieb.) Cavara & Grande Garlic Mustard
Eurasia; widespread and extensive in central and western Connecticut, becoming more so east of the Connecticut River; G&C-197.
Cardamine impatiens L.
Europe; common in western Connecticut and in the Connecticut River Valley, sporadic in eastern Connecticut; often overlooked; G&C-190.
Hesperis matronalis L. Dame's Rocket
Eurasia; increasingly common in rich soils across Connecticut; garden escape; G&C-196.
Lepidium latifolium L. Tall Pepperwort
Southern Europe and western Asia; dense stands occur along the coast and on coastal islands in Fairfield County, it has recently been found along the Mass. Turnpike near I-84 and northeastern Connecticut; G&C-181.
Nasturtium officinale R. Br. Watercress
Syn. Rorippa nasturtium-aquaticum (L.) Hayck.
Eurasia; sporadic across Connecticut in clear, quiet watercourses; possibly intentionally introduced and escaped from cultivation; G&C-193.


Cabomba caroliniana A. Gray Fanwort
Midwestern USA, probably not native here; common in eastern Connecticut; often dispersed by boats and boat trailers or aquarium enthusiasts; 1937; G&C-46.


Callitriche stagnalis Scop.
Europe; not known in Connecticut until recently; it appears to be invasive in streams and slow-moving rivers in western Connecticut, its current distribution and status elsewhere in Connecticut are unclear; 1993. G&C-459.


Lonicera japonica Thunb. Japanese Honeysuckle
Eastern Asia; widespread and common in Connecticut, especially near the coast; escaped from cultivation; dispersed by birds; G&C-509.
Lonicera maackii (Rupr.) Maxim. Amur Honeysuckle
Asia; sporadic in Connecticut; escaped from cultivation; dispersed by birds; G&C-509.
Lonicera morrowii A. Gray Morrow's Honeysuckle
Japan; probably widespread but sproradic; escaped from cultivation; dispersed birds; G&C-509.
Lonicera tatarica L. Tatarian Honeysuckle
Eurasia; commonly planted and probably sproradic as an escape from cultivation; dispersed by birds; G&C-509.
Lonicera xylosteum L. European Fly-honeysuckle
Europe; Connecticut status in the wild unclear, probably sporadic; escaped from cultivation; dispersed by birds; G&C-509.
Lonicera x bellaZabel Bella Honeysuckle
Hybrid of L. tatarica and L. morrowii; well established and widespread; escaped from cultivation; dispersed by birds; G&C-509.
Viburnum sieboldii Miq.
Japan; sporadic in woodlands and apparently increasing; probably dispersed by birds; G&C-512.


Celastrus orbiculatus Thunb. Asiatic Bittersweet
Eastern Asia; widespread and very common, probably in every town in Connecticut; escaped from cultivation; dispersed by birds; G&C-328.
Euonymus alatus (Thunb.) Sieb. Winged Euonymus
Eastern Asia; widespread and becoming increasingly common; escaped from cultivation; dispersed by birds; G&C-329.


Kochia scoparia (L.) Schrader Summer Cypress
Europe; common along the coast at the upper edges of salt marshes; maybe dispersed inland in bird seed mixes; G&C-99.


Elaeagnus umbellata Thunb. Autumn Olive
Eastern Asia; widespread and very common, probably in every town in Connecticut; escaped from cultivation as wildlife food and for rapid establishment against erosion; dispersed by birds; G&C-307.


Amorpha fruticosa
Southern and midwestern USA; common along major rivers in Connecticut. G&C-300.
Pueraria lobata (Willd.) Owhi Kudzu-vine
Japan; uncommon along coast, currently unknown inland in Connecticut; climbing on and over nearby vegetation, first Connecticut record 1928; at least one current population appears to be vegetative. C&G-305.


Geranium nepalense Sweet Nepalese Crane's-bill
Eastern Asia; local in Litchfield County; amazingly aggressive, highly competitive even with lawn grasses; 1981; G&C-360.


Myriophyllum spicatum L. European Water-milfoil
Europe; apparently increasing across the state as it is moved about by boats and boat trailers; 1979; G&C-308.


Egeria densa Planchon Brazilian Water-weed
Southeastern Brazil to northern Argentina; apparently increasing in ponds in southern Connecticut; it is commonly encountered as a plant used in aquaria and aquatic gardens and has probably accidentally escaped and become established; 1992; G&C-637.
Hydrilla verticillata (L. f.) Royle Hydrilla
"Old World"; currently known from only two ponds in the state, both in southeastern Connecticut, where it is amazingly aggressive; potentially a serious problem in any body of freshwater; dispersed by birds and boats; First Connecticut record - 1989; G&C-637.


Iris pseudacorus L. Yellow Iris
Europe; widespead and becoming increasingly common; escaped from cultivation; G&C-848.


Elsholtzia ciliata (Thunb.) Hylander Elsholtzia
Asia; sporadic, first Connecticut record - 1990; G&C-447.


Allium vineale L. Wild Garlic
Europe; widespread and common, especially in open fields and meadows, increasingly common in rich woodlands; dispersed by vegetative propagules; G&C-832.


Lythrum salicaria L. Purple Loosestrife
;Eurasia; widespread and common, one of our most visible invasive species when it dominates large parts of entire wetland systems; reproduces by seeds and vegetative propagules; a serious problem; G&C-311.


Ligustrum vulgare L. European Privet
Europe; widespread and sporadic, becoming increasingly common in natural areas, other Ligustrum species may be involved and worthy of consideration: primarily dispersed by birds; G&C-463.


Bromus tectorum L. Drooping Brome-grass
Europe; widespread in Connecticut but mostly in disturbed sites, sporadic in sand plain communities; G&C-773.
Microstegium vimineum (Trin.) A. Camus Japanese Stilt Grass
Tropical Asia; occasional and sporadic, mostly in southern parts of state, very likely to increase aggressively; first Connecticut report 1990 reported in 1980s; a serious problem in New Jersey and Pennsylvania; G&C-815.
Phragmites australis (Cav.) Trin. Common Reed
Cosmopolitan; widespread, very common, and very aggressive; G&C-781.
Poa compressa L. Canada Bluegrass
Europe; widespread and very common in open dry sandy soils and rocky woods and ledges; G&C-754.


Polygonum cuspidatum Sieb. & Zucc. Japanese Knotweed
Japan; widespread and very common, often occurs in areas of natural disturbance such as river or pond shores; escaped from cultivation; G&C-139.
Rumex acetosella L. Red sorrel
Eurasia; widespread and very common; frequently occurs on balds and rocky outcrops; G&C-130.


Potamogeton crispus L.
Europe; increasingly common in Connecticut, probably primarily dispersed by boats and boat trailers; 1908; G&C-642.


Ranunculus ficaria L. Lesser Celandine
;Eurasia; sporadic in southern Connecticut in rich woodlands and flood plain forests; G&C-59.


Frangula alnus Mill. European Buckthorn
Syn. Rhamnus frangula L.
Eurasia; widespread and very common, its wide ecological amplitude has allowed it to become established in a variety of habitats from wetland to upland woods and fields; escaped from cultivation, dispersed by birds; G&C-341.
Rhamnus cathartica L. Buckthorn
Eurasia; widespread but sporadic, frequent in northwestern Connecticut; escaped from cultivation; G&C-342.


Rosa multiflora Thunb. Multiflora Rose
Eastern Asia; widespread, very common, and aggressively spreading, usually encountered in open areas, it can be found in woodlands where it tenaciously persists; escaped from cultivation where it was used as a bank stabilizer and as a wildlife food; G&C-257.
Rubus phoenicolasias Maxim. Wineberry
Eastern Asia; widespread and common along the coast, sporadic but increasing inland; escaped from cultivation, its berries are attractive and delicious; G&C-251.


Ailanthus altissima (Mill.) Swingle Tree-of-heaven
Eastern Asia; widespread and common, especially near urban areas and along coast; escaped from cultivation; G&C-354.


Solanum dulcamara L. Climbing Nightshade
Eurasia; widespread and very common in a wide variety of habitats; probably bird dispersed but there is a paucity of reports of birds feeding on fruits; G&C-404.


Ampelopsis brevipedunculata (Maxim.) Chinaberry, Heartleaf Ampelopsis
Northeast Asia; widespread but sporadic, more commonly encountered near the coast; escaped from cultivation; G&C-343.

Appendix 1

Seemingly invasive non-native species that usually do not disperse far from site of original intentional introduction. Many grasses used as forage crops might be included here.


Vinca minorL. Common Periwinkle
Southern Europe; G&C-393.


Hedera helix L. English Ivy
Europe; G&C-364.


Pachysandra terminalis Siebold & Zucc. Pachysandra
Japan; G&C-332.


Euonymus fortunei Hand.-Mazz. Climbing Euonymus
China; not in G&C.


Coronilla varia L. Crown-vetch
Europe; G&C-286.
Cytisus scoparius (L.) Link Scotch Broom
Europe; G&C-277.
Lespedeza cuneata (Dum. Cours.) G. Don Chinese Lespedeza
Eastern Asia; G&C-298.


Akebia quinata Dcne. Akebia
Eastern Asia; G&C-65.


Hemerocallis fulva L. Orange Day-lily
Eurasia; G&C-830.


Clematis terniflora DC. Yam-leaved Clematis
Japan; G&C-54.


Rosa rugosa Thunb. Japanese Rose
Eastern Asia; G&C-257.
Sorbaria sorbifolia
Eastern Asia; G&C-241.

Appendix 2

Native or potentially native species that may have some populations that are non-indigenous and invasive.


Acer negundo L. Box-elder


Xanthium strumarium L. Common Cocklebur


Podophyllum peltatum L. May-apple


Myriophyllum heterophyllum Michx.


Phalaris arundinacea L. Reed Canary-grass

Appendix 3 -- Watch List; Questionable Problems

Taxa reported from Connecticut but that do not appear to be invasive at this time, however, these taxa are acknowledged problems as invasive aliens in nearby states or similar habitats. Aggressive invasiveness into "natural" habitats may be questionable. Please report any sites where these species appear to be aggressively invading natural habitats.


Acer platanoides L. Norway Maple
Europe; G&C-352.
Acer pseudoplatanus L. Sycamore Maple
Europe; G&C-352.


Aralia elata
Northeastern Asia; not in G&C.
Aralia spinosa
Southeastern USA; G&C-363.


Carduus nutans L.

Europe; G&C-610.

Cirsium arvense (L.) Scop.

Eurasia; G&C-613.
Cirsium vulgare(Savi) Tenore Bull-thistle
Eurasia; G&C-613.
Tussalago farfara
Eurasia; G&C-560.


Berberis vulgaris L. Barberry
Europe; G&C-64.


Alnus glutinosa (L.) Gaertner Black Alder
Eurasia and North Africa; not in G&C.


Myosotis scorpioides L. Forget-me-not.
Europe; G&C-422.


Butomus umbellatus L. Flowering Rush
Eurasia; G&C-632.


Humulus japonicusSieb. & Zucc. Japanese Hops
Eastern Asia; G&C-73.


Viburnum plicatum Thunb.
Eastern Asia; G&C-514.


Cycloloma atriplicifolium (Spreng.) Coult. Winged Pigweed
Midwestern USA; G&C-99.


Elaeagnus angustifolia L. Russian Olive
Eurasia; G&C-307.


Euphorbia cyparissias L. Cypress Spurge
Eurasia; G&C-338.
Euphorbia esula L. Leafy Spurge
Eurasia; G&C-338.


Robinia pseudoacacia L. Black Locust
Southeastern USA; G&C-280.


Fumaria officinalis L. Fumitory
Europe; G&C-70.


Ribes sativum Syme Garden Red Currant
Eurasia; G&C-228.


Myriophyllum aquaticum (Vell.) Verdc. Parrotfeather
South America; G&C-308.


Ajuga reptans L. Carpet-bugle
Eurasia; C&G-434


Ornithogalum umbellatum L. Star of Bethlehem
Europe; G&C-829.


Marsilea quadrifolia L. Water Shamrock
Europe; G&C-30.


Morus alba L. White Mulberry
Eastern Asia; G&C-75.


Najas minor Allioni European Water-nymph, Spiny Naiad
Old World; G&C-646.


Mirabilis nyctaginea (Michx.) MacM. Heart-leaved Umbrella-wort
Western USA; G&C-93.


Epilobium hirsutum L. Hairy Willow-herb
Eurasia and northern Africa; G&C-316.


Aira caryophyllea L. Silver Hairgrass
Europe; G&C-764.


Polygonum cespitosum Blume
Eastern Asia; G&C-137.


Lysimachia vulgaris L. Garden Loosestrife
Eurasia; G&C-222.


Galium mollugo L. Wild Madder
Eurasia; G&C-505.


Phellodendron japonicum Maxim. Cork-tree
Japan; G&C-356.


Populus alba L. White Poplar
Eurasia; G&C-167.


Datura stramonium L. Jimsonweed
Asia; C&G-406.


Taxus cuspidata Sieb. & Zucc. Japanese Yew
Japan, eastern Asia; G&C-32.


Valeriana officinalis L. Garden Heliotrope
Eurasia; G&C-516.

Appendix 4 -- Watch List; Anticipated Problems

Taxa not currently known to exist in Connecticut but might be anticipated because of populations nearby in adjacent states. In addition, any taxon included here is known to be invasive in similar habitats in other states.


Cirsium palustre (L.) Scop. Marsh-thistle
Invasive in upper Midwest, known from New Hampshire. Eurasia; G&C-613.


Impatiens glandulifera Royle
Invasive in parts of Maine and Maritime Provinces. Himalyan region; G&C-362.


Carex kobomugi Ohwi
Invasive on coastal dunes in New Jersey and New York, currently at on site along Rhode Island coast; eastern Asia; G&C-709.


Hydrocharis morsus-ranae L. European Frog's bit
Known to occur in Lake Champlain, Vermont. Europe; G&C-638.


Nymphoides peltata (Gmelin) Kuntze Yellow Floating-heart
Listed as an invasive in Massachusetts. Europe; G&C-413.


Glyceria maxima (Hartman) Holmburg Tall Mannagrass
Invasive in parts of the Midwest and Canada, currently known in New England from Massachusetts. Eurasia; not in G&C; see Anderson, J.E. &A.A. Reznicek. 1994. Glyceria maxima (Poaceae) in New England. Rhodora 96:97-101.


Polygonum perfoliatum L. Mile-a-minute Vine
Known to occur in Westchester County, New York, little more than 1 mile from the Connecticut line. First reported there in 1995 by which time it was well established. Eastern Asia; G&C-138.


Trapa natans L. Water Chestnut
Known to be invasive in eastern Massachusetts and along the Hudson River in New York. It has been reported near the Connecticut River in Massachusetts. Eurasia; G&C-313.
Last modified: Fri May 12 11:59:44 Eastern Daylight Time 2000