18 Common Invasive Plants in
New York State

The Invasive Plant Council of NYS has created the following list of the most invasive species in New York State. Plants are listed alphabetically - click on the pictures for fact sheets about each plant species [PDF files].

Autumn Olive (Elaeagnus umbellata) Autumn olive suppresses the growth of other plants by creating shade. It is a strong competitor because of its ability to fix nitrogen. If it is cut, it resprouts abundantly. Even burning does not rid the area of this plant, because it still resprouts from the stump.

Black Locust (Robinia pseudoacacia) Black locust rapidly spreads and crowds out native vegetation via root suckers.

Black and Pale Swallow-worts (Cynanchum nigrum and
C. rossicum)
Black and pale swallow-wort are vines that can grow rapidly—overgrowing native vegetation. They also have the ability to dominate the understory of a woodland. Wind-dispersed seeds allow it to disperse over long distances. When cut, plants resprout vigorously, making control difficult.

Common Reed (Phragmites australis)
Though some populations of this plant may well be native to parts of New York, common reed becomes problematic when it forms huge monocultures that spread for acres, excluding native species.

Common and Glossy Buckthorns (Rhamnus cathartica and R. frangula) Buckthorns have the ability to form dense thickets under which native vegetation cannot survive due to shading and crowding. Common buckthorn has a spine at the twig tips, the leaves are toothed, and the undersides of the leaves are smooth. Several native American buckthorns that occur in the eastern U.S. could be confused with the exotic species. If in doubt, consult with a knowledgeable botanist to get an accurate identification.

Curly-leaved Pondweed
(Potamogeton crispus)
Curly-leaved pondweed can form dense mats of vegetation on the surface of the water. These mats inhibit the growth of native aquatics, as well as interfere with boating and other water recreation.

Eurasian Water Milfoil
(Myriophyllum spicatum)
Eurasian water milfoil forms extremely dense mats of vegetation that can crowd out native aquatic plants. Mosquitoes find good breeding ground among the mats of vegetation. These dense mats of plants decompose, reducing the oxygen levels in the water body. These dense mats can also alter the temperature profile of a pond or lake. These plants have a negative effect on bird and fish habitat because of the reduction of oxygen, change in temperature, and change in pH that they cause. The roots overwinter—allowing their persistence in northern climates. New plants can grow from fragments, allowing the plant to be dispersed easily, by boats and waterfowl. The plant impedes recreational activities, such as swimming, fishing and boating.

Garlic Mustard (Alliaria petiolata)

Japanese Barberry (Berberis thunbergii) Japanese barberry forms dense stands in a variety of habitats ranging from closed canopy forests to woodlands, wetlands, pastures, meadows and wasteland. It is readily dispersed by birds, which can bring the seeds many meters away from the parent plants. Though the exact effect on native flora is not determined, Japanese barberry could prove a great threat to native species.

Japanese Honeysuckle
(Lonicera japonica)
Japanese honeysuckle is an extremely vigorous grower and can cover trees and understory shrubs. The weight of the vines can help to bring down trees. This plant not only competes aboveground, but below as well. Due to the Japanese honeysuckle's dominance of the understory, native tree seedlings and herbaceous plants are unable to grow.

Japanese Knotweed
(Polygonum cuspidatum)
The threat of this plant was first recognized in Britain where it has been present for a longer period of time. There, it is a great threat to riparian areas and wetlands.

Japanese Stilt Grass
(Microstegium vimineum)
Japanese stilt grass forms monotypic stands that can completely dominate the understory of a forest. These dense stands crowd out native species of vegetation.

Norway Maple (Acer platanoides)
Norway maple is able to shade out native understory vegetation, for example, spring ephemerals, and eventually out-compete native tree species in the forest canopy. Thus, it can reduce native species diversity and change the structure of forest habitats.

Oriental Bittersweet
(Celastrus orbiculatus)
Oriental bittersweet destroys native plants by overgrowing them. Shading by the vigorous growth of the vine, and girdling of plants causes major damage. The native climbing bittersweet vine (Celastrus scandens) can easily be confused with this invasive. Climbing bittersweet has flowers at the tips of the stems rather than along the stems.

Purple Loosestrife (Lythrum salicaria) This plant has the ability to completely dominate a wetland setting, forming a vast, monotypic stand. These stands prevent the establishment of native wetland plants. Purple loosestrife also affects native wildlife that may not be able to use the plants as effectively for food or cover. By forming these dense stands, purple loosestrife can clog waterways causing problems for both commercial and recreational uses of these areas.

Spotted or Bush Knapweed
(Centaurea maculosa)
Once established in a disturbed site, spotted knapweed can invade nearby undisturbed sites with a slow frontal expansion. It competes with native vegetation and can decrease local species diversity. It gives off an allelopathic compound called cnicin that is capable of retarding the root growth of neighboring plants. Its roots have poor soil holding capabilities; therefore, spotted knapweed tends to promote soil erosion.

Water Chestnut (Trapa natans) Threats from water chestnut are a result of the surface mats it forms, causing competition for nutrients and space. This plant has little nutritional value for wildlife. Its blooms and decomposition could also contribute to lower levels of dissolved oxygen in shallow water, and its spiny fruit can founder horses or dogs. Furthermore, the spread of the water chestnut can have economic impacts resulting from the plant’s ability to impede fishing, hunting, swimming, boating and commercial navigation.

Sources:

Invasive species information is from the Invasive Plant Council of New York State, the National Park Service and US Fish and Wildlife Service publication Plant Invaders of Mid-Atlantic Natural Areas, and the Invasive Plant Atlas of New England.

Multiflora rose image credit: Jil M. Swearingen, USDI National Park Service, www.forestryimages.org.