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
Leslie J. Mehrhoff
George Safford Torrey Herbarium
!! THIS LIST HAS NO LEGAL STATUS !!
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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
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
|Froelichia gracilis (Hook.) Moq.
- Southwestern U.S.; sporadic along major highways; 1973;
|Aegopodium podagraria L.
- Eurasia; invasive along streams; commonly planted and escaping
from cultivation; G&C-371.
|Vincetoxicum nigrum (L.)
- Europe; widespread and and increasingly common; wind dispersed;
|Vincetoxicum rossicum (Kleo.)
- Europe; overlooked until recently, this species is common along
coast and sporadic inland; wind dispersed; 1881; not in
- Europe; widespread along roadsides and disturbed areas,
potentially a problem in early succussional habitats;
- Japan; widespread and common, can form large monotypic stands in
forest understory; bird dispersed; G&C-64.
- 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
- Eurasia; widespread and extensive in central and western
Connecticut, becoming more so east of the Connecticut River;
- Europe; common in western Connecticut and in the Connecticut
River Valley, sporadic in eastern Connecticut; often
|Hesperis matronalis L.
- Eurasia; increasingly common in rich soils across Connecticut;
garden escape; G&C-196.
|Lepidium latifolium L.
- 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.
- Syn. Rorippa nasturtium-aquaticum (L.) Hayck.
- Eurasia; sporadic across Connecticut in clear, quiet
watercourses; possibly intentionally introduced and escaped from
- Midwestern USA, probably not native here; common in eastern
Connecticut; often dispersed by boats and boat trailers or
aquarium enthusiasts; 1937; G&C-46.
- 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.
- Eastern Asia; widespread and common in Connecticut, especially
near the coast; escaped from cultivation; dispersed by birds;
|Lonicera maackii (Rupr.)
- Asia; sporadic in Connecticut; escaped from cultivation;
dispersed by birds; G&C-509.
- Japan; probably widespread but sproradic; escaped from
cultivation; dispersed birds; G&C-509.
|Lonicera tatarica L.
- Eurasia; commonly planted and probably sproradic as an escape
from cultivation; dispersed by birds; G&C-509.
|Lonicera xylosteum L.
- Europe; Connecticut status in the wild unclear, probably
sporadic; escaped from cultivation; dispersed by birds;
|Lonicera x bellaZabel
- Hybrid of L. tatarica and L. morrowii; well
established and widespread; escaped from cultivation; dispersed
by birds; G&C-509.
- Japan; sporadic in woodlands and apparently increasing; probably
dispersed by birds; G&C-512.
- Eastern Asia; widespread and very common, probably in every town
in Connecticut; escaped from cultivation; dispersed by birds;
|Euonymus alatus (Thunb.)
- Eastern Asia; widespread and becoming increasingly common;
escaped from cultivation; dispersed by birds; G&C-329.
|Kochia scoparia (L.)
- Europe; common along the coast at the upper edges of salt
marshes; maybe dispersed inland in bird seed mixes;
- 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;
- Southern and midwestern USA; common along major rivers in
|Pueraria lobata (Willd.)
- 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.
- Eastern Asia; local in Litchfield County; amazingly aggressive,
highly competitive even with lawn grasses; 1981;
- Europe; apparently increasing across the state as it is moved
about by boats and boat trailers; 1979; G&C-308.
|Egeria densa Planchon
- 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;
(L. f.) Royle
- "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.
- Europe; widespead and becoming increasingly common; escaped from
|Elsholtzia ciliata (Thunb.)
- Asia; sporadic, first Connecticut record - 1990;
|Allium vineale L.
- 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.
- ;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.
- Europe; widespread and sporadic, becoming increasingly common in
natural areas, other Ligustrum species may be involved
and worthy of consideration: primarily dispersed by birds;
|Bromus tectorum L.
- Europe; widespread in Connecticut but mostly in disturbed sites,
sporadic in sand plain communities; G&C-773.
|Microstegium vimineum (Trin.)
||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.)
- Cosmopolitan; widespread, very common, and very aggressive;
|Poa compressa L.
- Europe; widespread and very common in open dry sandy soils and
rocky woods and ledges; G&C-754.
Sieb. & Zucc.
- Japan; widespread and very common, often occurs in areas of
natural disturbance such as river or pond shores; escaped from
|Rumex acetosella L.
- Eurasia; widespread and very common; frequently occurs on balds
and rocky outcrops; G&C-130.
- Europe; increasingly common in Connecticut, probably primarily
dispersed by boats and boat trailers; 1908; G&C-642.
|Ranunculus ficaria L.
- ;Eurasia; sporadic in southern Connecticut in rich woodlands and
flood plain forests; G&C-59.
|Frangula alnus Mill.
- 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.
- Eurasia; widespread but sporadic, frequent in northwestern
Connecticut; escaped from cultivation; G&C-342.
- 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.
- 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.)
- Eastern Asia; widespread and common, especially near urban areas
and along coast; escaped from cultivation; G&C-354.
|Solanum dulcamara L.
- 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.
||Chinaberry, Heartleaf Ampelopsis
- Northeast Asia; widespread but sporadic, more commonly
encountered near the coast; escaped from cultivation;
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.
- Southern Europe; G&C-393.
|Hedera helix L.
- Europe; G&C-364.
|Pachysandra terminalis Siebold
- Japan; G&C-332.
- China; not in G&C.
|Coronilla varia L.
- Europe; G&C-286.
|Cytisus scoparius (L.)
- Europe; G&C-277.
(Dum. Cours.) G. Don
- Eastern Asia; G&C-298.
|Akebia quinata Dcne.
- Eastern Asia; G&C-65.
|Hemerocallis fulva L.
- Eurasia; G&C-830.
- Japan; G&C-54.
|Rosa rugosa Thunb.
- Eastern Asia; G&C-257.
- Eastern Asia; G&C-241.
Native or potentially native species that may have some
populations that are non-indigenous and invasive.
|Acer negundo L.
|Xanthium strumarium L.
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.
- Europe; G&C-352.
|Acer pseudoplatanus L.
- Europe; G&C-352.
- Northeastern Asia; not in G&C.
- Southeastern USA; G&C-363.
Carduus nutans L.
- Europe; G&C-610.
Cirsium arvense (L.)
- Eurasia; G&C-613.
- Eurasia; G&C-613.
- Eurasia; G&C-560.
|Berberis vulgaris L.
- Europe; G&C-64.
|Alnus glutinosa (L.)
- Eurasia and North Africa; not in G&C.
- Europe; G&C-422.
|Butomus umbellatus L.
- Eurasia; G&C-632.
japonicusSieb. & Zucc.
- Eastern Asia; G&C-73.
- Eastern Asia; G&C-514.
- Midwestern USA; G&C-99.
- Eurasia; G&C-307.
- Eurasia; G&C-338.
|Euphorbia esula L.
- Eurasia; G&C-338.
- Southeastern USA; G&C-280.
|Fumaria officinalis L.
- Europe; G&C-70.
|Ribes sativum Syme
||Garden Red Currant
- Eurasia; G&C-228.
- South America; G&C-308.
|Ajuga reptans L.
- Eurasia; C&G-434
||Star of Bethlehem
- Europe; G&C-829.
- Europe; G&C-30.
|Morus alba L.
- Eastern Asia; G&C-75.
|Najas minor Allioni
||European Water-nymph, Spiny Naiad
- Old World; G&C-646.
- Western USA; G&C-93.
|Epilobium hirsutum L.
- Eurasia and northern Africa; G&C-316.
|Aira caryophyllea L.
- Europe; G&C-764.
- Eastern Asia; G&C-137.
- Eurasia; G&C-222.
|Galium mollugo L.
- Eurasia; G&C-505.
- Japan; G&C-356.
|Populus alba L.
- Eurasia; G&C-167.
|Datura stramonium L.
- Asia; C&G-406.
|Taxus cuspidata Sieb. &
- Japan, eastern Asia; G&C-32.
- 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.)
- Invasive in upper Midwest, known from New Hampshire. Eurasia;
- Invasive in parts of Maine and Maritime Provinces. Himalyan
- Invasive on coastal dunes in New Jersey and New York, currently
at on site along Rhode Island coast; eastern Asia;
||European Frog's bit
- Known to occur in Lake Champlain, Vermont. Europe;
|Nymphoides peltata (Gmelin)
- Listed as an invasive in Massachusetts. Europe;
|Glyceria maxima (Hartman)
- 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.
- 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;
|Trapa natans L.
- 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