Invasive Species

What are invasive plants? Invasive plants are non-native species that have been introduced, either intentionally or accidentally, from another geographic area. They are one of the top three causes of species extinctions world-wide. They out-compete native plants that are important to wildlife and decrease biodiversity in natural areas. Invasives can quickly dominate a landscape – just a few plants can spread rapidly, if not located, identified and dealt with immediately. They cost the US economy billions of dollars in impacts to recreation, agriculture and control. Early detection and rapid removal is the most efficient approach to control. Removal methods vary according to type of plant, extent of infestation, and habitat type.
For information on identification and removal methods for the species featured, log on to the following websites:
     The Connecticut Invasive Plant Working Group
     The Invasive Plant Atlas of New England

To View Larger Photos, Simply Click on the Thumbnail Version.

Black Locust (Robinia pseudo-acacia)

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Black Locust
Tree. Native to some parts of eastern North America but introduced to New England for erosion control and for its highly rot-resistant wood which was extensively used for fence posts.
  • Mature trees have deeply furrowed bark.
  • Branches have short spines and produce flat, brown pods 2-4 in. long that often remain on tree into winter.
  • Leaves are compound and comprised of 7-19 oval leaflets that drop in early fall.
  • Flowers hang in showy clusters and are fragrant.
The Problem:
Spreads fast by root suckers, quickly out-competing native vegetation, especially in floodplains; prefers well-drained sandy soils. Nitrogen-fixing nodules on roots alter soil chemistry of natural sand-plain communities, a rare habitat type in CT.

Burning Bush (Euonymus alata)

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Burning Bush
Large, ornamental bush, up to 10’ in height. Prevalent along riverbanks and in rich forest soils; also found in open areas.

  • “Winged” ridges on stems are characteristic.
  • Leaves are opposite.
  • Leaf color in fall: bright red (full sun); pale pink (shade).
  • Oval berries ripen from green to red in late summer.
The Problem:
Escapes from planted landscapes into natural areas, rapidly developing into dense colonies; displaces native understory shrubs important to songbirds. Infestations can be many acres in size.
Remains popular in nursery trade due to ease of propagation (high profit margin), fast growth rate, and brilliant red fall color.

Coltsfoot (Tussilago farfara)

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Perennial. Medicinal herb. Most likely introduced by European settlers.

  • Dandelion-like flowers emerge in early spring (sometimes through snow) before its leaves.
  • Leaves range from heart-like to roundish in shape with coarsely toothed edges.
  • Forms dense stands in moist soils of watercourses, forests and meadows.
  • Thrives in partial shade, but tolerates full sun.
The Problem:
Forms large colonies that spread quickly by rhizomes. These underground stems can grow 10 ft. deep, making digging out difficult. Small seeds have tuft of hairs, aiding wind dispersal over long distances.

Common Buckthorn (Rhamnus cathartica) & Glossy Buckthorn (Frangula alnus)

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Common Buckthorn
Both species are shrubs and were introduced before 1800. Both are native to Europe, Asia and
northern Africa.

  • Buckthorn species are difficult to separate when not in fruit.
  • Consult referenced websites for distinguishing features.
The Problem:
Non-native buckthorns are highly invasive and are easily overlooked due to their similarity to native cherry species (Prunus sp.) and native buckthorns. Both species spread rapidly due to prolific fruit production, forming impenetrable stands. Birds are the primary dispersal agents.

Common Reed (Phragmites australis)

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Common Reed
Grass, 6-13’ in height. History of introduction unclear.

  • Tall grass with plume-like flowers.
  • Leaves are gray-green in color.
  • Dry flower stems remain standing throughout winter.
  • There is also a rare, native genotype.
Know how to separate the two before eradicating!
The Problem:
Spreads rapidly, especially in floodplains and wetlands where it forms huge stands, excluding other plants. Releases chemicals toxic to other plants thereby preventing their establishment (allelopathic).

Garlic Mustard (Alliaria petiolata)

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Garlic Mustard
Biennial herb. Introduced by settlers for food and medicinal purposes. Tolerates both sun and shade.

  • First year plants are a rosette of leaves; second year plants produce a central stem with tiny white flowers.
  • Leaves are coarsely toothed and emit characteristic garlicky odor when crushed.
  • Plants remain green in winter.
The Problem:
Spreads rapidly, especially in floodplains where seeds are dispersed by water. Out-competes native early spring wildflowers (important to pollinators), like bloodroot and Dutchman’s breeches, by releasing chemicals preventing their growth (allelopathy).

Goutweed (Aegopodium podagraria)

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Herbaceous perennial. Most likely introduced as an ornamental ground cover; first reported in the 1860’s from Rhode Island.

  • Inflorescence similar to that of Queen Anne’s lace and composed of tiny white flowers.
  • Leaves have long stems but variable in shape; lower leaves can have 9 leaflets.
  • Leaves can be green or variegated (white edges).
  • Some native plants have similar leaves and flowers. Know the difference!
The Problem:
Escapes from planted landscapes into natural areas, rapidly developing into dense colonies. Displaces native spring ephemerals in floodplain areas. Difficult to eradicate due to prolific root system; digging can exacerbate infestations as it can trigger root fragments to sprout. Fragments easily transported by water.

Japanese Barberry (Berberis thunbergii)

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Japanese Barberry
Shrub; 2-8’ tall. Common in floodplain forests and in open areas. Introduced as an ornamental for hedgerows.
Blooms mid-spring.

  • Branches are grooved and have spines.
  • Pale yellow flowers are small and run along entire length of stem.
  • Produces bright red, oval berries that remain on stem through winter.
  • Shrubs are usually very dense.
The Problem:
Plants are highly shade tolerant, capable of forming dense, impenetrable stands in closed-canopy riverine forests. Spreads primarily by birds, especially turkeys.

Japanese Knotweed (Polygonum cuspidatum)

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Japanese Knotweed
Woody perennial, up to 10’ tall. Common along streams and moist soils along roadsides.

  • Stems are bamboo-like.
  • Flowers are small and white, in plume-like clusters.
  • Blooms in late summer, from August into fall.
The Problem:
Plants spread primarily by underground stems (rhizomes) 20+ ft. in length from which new colonies emerge. Out-competes riparian vegetation that supports insects important to native brook trout and other species; reduces nesting areas of stream-dependent birds. Extremely difficult to eradicate due to extensive root system.

Japanese Stilt Grass (Microstegium vimineum)

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Japanese Stilt Grass
Low-growing, annual grass. Introduced to US as packing material in porcelain imports. First documented from environment in early part of last century but relative newcomer to Litchfield County.

  • Silvery stripe in center of leaf is diagnostic.
  • Joints on stems produce roots which grow into new plants.
  • In fall changes from green to straw color, tinged with burgundy red.
  • Often grows w/native white grass (perennial) with which it is often confused. (White grass lacks silvery stripe on leaf and stems are encircled by ring of small hairs.)
The Problem:
Impedes forest regeneration due to sheer density of growth, by preventing native plant seedling development. Can also cause soil erosion, especially on stream banks as its roots, which would otherwise help stabilize soil, die in winter. Spreads rapidly due to prolific seed production; large colonies take time to eradicate due to vast number of seeds present in soil.

Mile-A-Minute Vine or Devil’s Tearthumb (Persicaria perfoliata)

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MAM Vine - Photo by Todd L. Mervosh, Ph.D.
Annual vine with elongated, branched stems that can climb into trees and reach lengths of more than 20 feet. Native to Japan, Korea, China, Taiwan and India.

  • Branches and stems are covered with small barbs and can have a reddish color.
  • Leaves are simple, alternate, triangular and 1”-3” wide.
  • The mid-vein of the leaf also has barbs.
  • A very distinct saucer-shaped bract encircles the stems at each node.
  • New plants can be seen in late April or early May.
  • Metallic-blue colored fruits ripen from September to November.

The Problem:
Extremely rapid growth of up to 6” per day, enabling it to form dense mats that smother seedlings and/or native plants. Mile-a-Minute (MAM) fruits are clusters of several small berries, each containing one spherical seed that turns black when mature. In sunny sites, some fruits begin to ripen from green to blue by mid July (much earlier than Sept.-Nov.). Of course, the goal is to control MAM before its seeds are viable, and that can happen even before the fruits have fully ripened.

Management: Mowing, cutting or hand removal can be used to manage this weed. To avoid the barbs, remember to wear gloves for hand removal of this plant. Action should be taken before
large, dense areas form and before seed set. All plant debris should be removed from the site to
ensure that no viable seeds are left behind. In agricultural settings, there are registered herbicides that will kill Mile-A-Minute.

Multiflora Rose (Rosa multiflora)

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Multiflora Rose
Shrub, up to 15’ in height. Prevalent along riverbanks and in rich forest soils; also found
in open areas.

  • Flowers can be white or pink; fragrant.
  • Stems are red or green in color and have prickers.
  • Leaves are elliptical and smooth with serrated margins.
  • Fruit are red and nearly spherical.
The Problem:
Escapes from planted landscapes into natural areas, rapidly developing into dense colonies; displaces native understory shrubs important to songbirds. Infestations can be many acres in size.
Remains popular in nursery trade due to easy propagation (high profit margin), fast growth rate, and brilliant red fall color.

Norway Maple (Acer platanoides)

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Norway Maple
Tree. Introduced in 1756; extensively planted as an ornamental.

  • Bark is grayish and smooth with a network of low ridges.
  • Leaf stems exude a white sap when broken off twig.
  • Flowers, which appear very early in spring (April) are yellow-green in color.
  • Paired, papery fruit are divergent, nearly 180º apart.
  • Retains leaves into late fall which often have round, black, fungal spots this time of year.
The Problem:
Escapes from planted landscapes into natural areas where it out-competes native vegetation, reducing forest diversity.

Oriental Bittersweet (Celastrus orbiculatus)

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Oriental Bittersweet
Woody vine, up to 60’. in height. Introduced as an ornamental; used in wreath-making and in floral displays for its showy, orange “berries”.

  • Stems have brown striated bark.
  • Profusion of orange, berry-like fruit produced in fall.
  • Leaves vary in shape from elliptical to nearly round.
  • Flowers are small and insignificant (greenish in color).
  • Often seen wrapped around tree trunks.
  • Similar to our rare, native bittersweet which has fruit only at ends of branches!
The Problem:
Kills trees and shrubs by girdling and blocking out sunlight; sometimes trees collapse due to sheer weight of vines.

Porcelainberry (Ampelopsis brevipedunculata)

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Perennial vine; grows up to 20 ft. high. Introduced from Asia as an ornamental and for screening.

  • Leaves highly variable in shape but most are similar to those of grape.
  • Fruit are small and grow in clusters; color ranges from yellow to green, turning to light blue.
  • Its small green flowers are inconspicuous.
  • Like grapes, stems have tendrils.
The Problem:
Often overlooked due to its similarity to grape. Out-competes grape species, an important wildlife food, and other native plants. Weight of vine makes underlying plants more susceptible to wind and ice damage. Fruit dispersed long distances by water and birds. Very difficult to eradicate!

Purple Loosestrife (Lythrum salicaria)

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Purple Loosestrife
Herbaceous perennial, up to 6’ tall. Familiar invaders of wetlands but can also be found along streams and rivers; requires full sun.

  • Purple flowers, from mid-summer into fall.
  • Found in wet soil.
  • Leaves are opposite or in whorls of three.
The Problem:
Releases chemicals that prevent growth of other plant species (allelopathy) and stunt amphibian development. Produces huge stands that clogs waterways, impeding recreational activities and reducing wetland biodiversity.

Shrub Honeysuckle (Lonicera sp.)

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Shrub Honeysuckle
Shrub; up to 8’ tall. Common in forests along rivers and streams and along edges. Introduced as an ornamental.

  • Flowers are pink, or white and fading to yellow.
  • Flowers May-early June.
  • Fruit are red and round in shape.
  • Stems are hollow.
The Problem:
Fruit eaten and dispersed primarily by birds. Plants create extensive, dense colonies, displacing native understory shrubs.