People who spend time in wetlands in Wisconsin are used to encountering invasive plants like reed canary grass, hybrid cattails and purple loosestrife. And phragmites is popping up in more wetlands each year. However, compared to forest and grassland habitats, the number of invasive plants spreading in Wisconsin’s wetlands is relatively small. Yet there is a growing number of potential wetland invaders that may pose future threats to our wetlands, especially to riverine and lacustrine wetlands (wetlands associated with rivers and lakes, respectively).
Fortunately, there are no known populations in Wisconsin of other potential wetland invaders like mile-a-minute, Chinese yam, kudzu, Japanese stilt grass, spreading hedge parsley, pale swallow-wort, European frog-bit, Brazilian waterweed, fanwort, parrot feather, hydrilla, or water chestnut. Keep watching for these species - the key to preventing the establishment and spread of these species is to spot and remove them early. With diligent identification, reporting, control and monitoring, we can keep them from dominating our remaining high quality wetlands.
Below you can read about and view photos of new invasive plants to watch for in your local wetlands and learn how you can be a part of the effort to stop their spread.
FLOODPLAIN & SHORELINE INVADERS
Japanese hops (Humulus japonicus)
Unlike the native hops and the beer hops, this Asian species consistently has 5 lobed leaves. Stiff hooked climbing hairs help it to climb over and blanket other vegetation. The weed-watcher program has resulted in three populations of this hops being found in the state, one of which covers several acres along a stream shore. Floodplains and open disturbed areas can also be invaded.
> Photos and more info for this species.
Mile-a-minute (Polygonum perfoliatum)
Mile-a-minute is an herbaceous, annual, trailing vine similar in appearance to tear-thumb. The leaves are alternate, light green, shaped like an equilateral triangle, and have barbs on the underside. The delicate, narrow, reddish stems can grow to 20 feet, have curved downward pointing barbs and are surrounded at intervals by circular, cup shaped leafy structures, known as ocreas. Small, inconspicuous white flowers, and segmented, metallic blue fruits emerge from within the ocreas. The barbed stem and rapid rate of growth (up to six inches a day) allows this plant to climb over natives. Mile-a-minute generally colonizes moist open or disturbed areas such as edges of woods and streams. Currently it is found from OH to NY and WV, but it isn’t known if it is limited by cold weather.
> Photos and more info for this species.
Chinese yam or Cinnamon vine (Dioscorea oppositifolia)
Chinese yam, native to Asia, is an herbaceous, perennial vine. Highly invasive, it forms mat-like colonies that blanket and shade-out nearby vegetation. It is spreading rapidly in southern Illinois, primarily along forested streamsides, where it spreads by aerial bulbils floating downstream. These bulbils can germinate within two weeks of reaching open soil and will grow into vertical tubers up to 3 feet long.
> Photos and more info for this species.
Japanese knotweed (Polygonum cuspidatum syn. Fallopia japonica)
Often mistakenly called "Mexican bamboo", this semi-woody perennial is commonly found in upland urban areas where it was planted years ago. It spreads rapidly by rhizomes forming large, dense thickets that eliminate native vegetation and wildlife habitat. Although it is already somewhat widespread in much of the state, it is generally not yet in the habitats where it is likely to become extremely invasive. Once it gets into the shore of a river, stream or lake, knotweed can spread by root fragments, forming thickets lining the shores for miles and causing extensive shoreline erosion. Once established, large dense stands are difficult to eradicate.
> Photos and more info for this species.
Japanese stilt grass (Microstegium vimineum)
This annual grass has the capacity to very rapidly invade forests, especially in floodplains where the seeds are readily dispersed. In one season it germinates, grows 3-5 feet in height, and produces seed by fall. It looks like a small bamboo, with three inch alternate leaves with a white stripe down the middle. The dense tangled mat of stems completely covers the forest floor, preventing the growth of other plants. The dead stems are very flammable, increasing the danger of any fires.
> Photos and more info for this species.
Additional plants that may become invasive in floodplains, but are also found in uplands:
Tree of heaven (Ailanthus altissima)
Ironically named, tree-of-heaven, is a very fast growing weedy tree, growing a meter a year and reaching up to 80’. Currently it is primarily found in urban areas in souther Wisconsin. However, this tree is rapidly spreading in forests in the states to our south and east. In forests it quickly reaches the canopy and shades out mature trees. It also produces toxins that can prevent the establishment of other plant species. The most distinctive characteristics of this deciduous tree are its foul odor, four foot long compound leaves and inch diameter stems on new growth.
> Photos and more info for this species.
Oriental bittersweet (Celastrus orbiculata)
Easily confused with the native American bittersweet, the Oriental bittersweet is a serious threat to grasslands, woodland edges, forests, and beaches. This woody climbing vine is capable of over-topping tall trees, shading, girdling, and eventually pulling them down. Oriental bittersweet vines grow up to 60 feet high and 4 inches in diameter. American bittersweet has leaves with a more tapered tip and larger fruit clusters at the ends of stem and the fruits are produced in small clusters at the leaf axils. There are a number of scattered infestations known in Wisconsin, but it is not yet widespread.
> Photos and more info for this species.
Porcelain-berry* (Ampelopsis brevipedunculata)
Sometimes planted as an ornamental, this is a deciduous, woody vine related to grapes. It can be extremely aggressive, shading out native vegetation by blanketing the ground and climbing trees and shrubs using its tendrils. In forests in the Mid-Atlantic States it grows rapidly along forest edges, trails, roadsides, riparian and open areas. Wildlife eat the distinctive pink, blue and lavender fruits, then inadvertently disperse the seeds. We currently know of only a few infestations in WI, although it is much more abundant to the south and east. It is reported that only the green-leaved variety is invasive and that the variegated cultivar appears to be benign.
> Photos and more info for this species.
Kudzu (Pueraria lobata)
In southern states, kudzu is well-known for its ability to cover large trees, forest edges, utility lines, billboards, abandoned houses, and anything in its path. Nearby vegetation dies for lack of sunlight. A single kudzu root can produce up to 30 vines that can grow up to a foot a day and 60 feet per summer. It quickly girdles and blankets shrubs and trees, breaking branches and uprooting entire trees under its weight. Kudzu reproduces via runners, rhizomes, vines that root at the nodes, and hard-coated seeds dispersed by wind, water, and animals. This perennial legume has large three parted leaves and reddish purple flowers that produce flat brown pea-like pods. Although no populations have been found in Wisconsin yet, recent research found that the northern-most population has been producing viable seeds. Those plants were found in Evanston, IL, about 30 miles south of the border.
> Photos and more info for this species.
Japanese honeysuckle (Lonicera japonica)
This semi-evergreen woody vine resembles native honeysuckle vines, but it has pairs of white, cream, or pink flowers, hairy opposite leaves, and produces purplish black berries. Japanese honeysuckle spreads in woodland edges, floodplains, fields and roadsides. The vines typically grow six to ten feet in height, but can reach up to 30 feet, forming dense inter-twining mats that out-compete native vegetation for light, water and nutrients, and topple shrubs and trees. Japanese honeysuckle reproduces via underground stems (rhizomes) and seed that are dispersed by birds. Toxins from the vine may inhibit the regeneration of some trees. It is abundant in central IL and seems to be expanding northward. There may be ornamental cultivars that are not invasive.
> Photos and more info for this species.
Black and pale swallow-wort (Vincetoxicum nigrum, V. rossicum)
These vining milkweeds have tough stems that wind around and smother adjacent vegetation and can climb over ten feet into trees. They can thrive in full sun or shade and in moist to dry soils. Unlike most of our native milkweeds, their glossy dark leaves do not have milky sap. Small dark flowers develop into milkweed type pods with wind-borne seeds. Where found in Wisconsin, black swallow-wort has spread widely, creating rapidly growing mats of tangled vines. Photos and more info for
> black swallow-wort and pale swallow-wort.
Japanese and spreading hedge parsley (Torilis japonica, T. arvensis)
Although property managers have only been aware of this invader in the last 5-10 years, it has become very abundant in some areas, completely displacing native plants in forests, fields and wetlands. The hedge parsleys are biennials in the carrot family with small umbels of white flowers and dark fern-like compound leaves. The seeds have small barbs, aiding them in being dispersed rapidly to new sites. This plant may have the capacity to spread even more rapidly than garlic mustard. Photos and more info for
> Japanese hedge parsley and spreading hedge parsley.
SHALLOW WATER INVADERS
Flowering rush (Butomus umbellatus)
This perennial aquatic plant can be entirely submerged in deep water, or emergent in shallow waters, shorelines and marshes with standing water. Emergent leaves stand about three feet high and resemble bur-reeds. The spray of white, pink to purple three-petaled flowers is very distinctive. Spreading by rhizomes, flowering rush can form dense colonies.
> Photos and more info for this species.
European frog-bit (Hydrocharis morsus-ranae)
These free-floating aquatic plants look like miniature white water lilies. Thick mats are formed from long horizontal submerged stems. Shallow ponds, shores and marshes can become blanketed with the floating plants.
> Photos and more info for this species.
Pond water-starwort (Callitriche stagnalis)
Native to both Europe and North Africa, this plant has been found in the states in the northeast, northwest, and a few sites in Wisconsin. Pond water-starwort is found in ponds, marshes and streams. It is capable of creating locally dense mats of vegetation that may crowd out native aquatic vegetation. The floating stems have small, densely packed oval leaves that form overlaid crosses and tiny inconspicuous flowers.
> Photos and more info for this species.
Yellow floating heart (Nymphoides peltata)
Yellow Floating Heart, native to Eurasia and the Mediterranean, is a perennial, water-lily like plant. This plant has frequently been planted as an ornamental in water gardens. It can form large floating mats in slow moving rivers, lakes, reservoirs, ponds, and swamps. Infestations occur in northern Indiana and northern Illinois, but have not yet been found in WI. It looks like a small yellow water lily, with floating leaves just over an inch across and flowers held above the water.
> Photos and more info for this species.
Additional plants that are invasive primarily in lakes and streams:
Brazilian waterweed (Egeria densa)
Brazilian waterweed is a submersed, freshwater, perennial herb, usually rooted in the substrate but in some cases, drifting. Its stems are cylindrical and simple or branched, and typically grow one to two feet, but can reach lengths of 20 feet. Leaves grow in whorls of 3 to 8 with short internodes making the plant look very leafy. It is most prevalent on the west coast and is known in southern Illinois, but is not yet in Wisconsin. It grows in still and flowing waters such as lakes, ponds, pools, ditches, quiet streams and seems to grow best in mildly acidic, nutrient-rich lakes. Reproducing via fragmentation allows it to spread from a single plant and tends to choke out slower-growing native plants. It can also outcompete Eurasian water milfoil.
> Photos and more info for this species.
Carolina fanwort (Cabomba caroliniana)
Fanwort is a freshwater, submersed, perennial plant with short, fragile rhizomes. It is usually rooted in the substrate, but sometimes found drifting. Its stems are green to reddish brown. It has two types of leaves: submersed and floating. The submersed leaves are arranged in pairs or in whorls along the stem and the floating leaves are diamond shaped and are arranged in an alternating pattern. It has small white, pink or purple flowers that float on the surface and grow from the tips of the stems. Considered weedy even in its native range, it has created severe nuisance conditions as far north as New York, Michigan, and Oregon.
> Photos and more info for this species.
Parrot feather (Myriophyllum aquaticum)
Parrot feather is an herbaceous aquatic plant that grows to a length of 6.5 to 16 feet. Its stems are greenish blue with numerous small leaves that resemble feathers. Emergent stems are bright green in color and can reach up to a foot above the water surface. Parrot feather provides ideal mosquito larvae habitat and shades out algae that serve as the basis for the aquatic food chain. Infestations can also hinder water movement in lakes, ponds and streams. It has naturalized throughout southern states and northward as far as Idaho, Washington and New York. It grows best in still waters such as lakes, ponds, quiet streams and drainage ditches, but is able to survive in rivers. Vegetative reproduction is the only dispersal agent because female plants are not found in the United States.
> Photos and more info for this species.
Hydrilla (Hydrilla verticillata)
This submerged plant can spread prolifically, completely dominating the water from shorelines to twenty feet deep. Looking similar to our native Elodeas, it has small leaves in whorls of 4-8. This tenacious plant can reproduce by stem or root fragments, tubers and turions (compact buds that overwinter). Recently found spreading in northern Indiana, lakes managers are concerned that this plant will be very troublesome if introduced to Wisconsin waters.
> Photos and more info for this species.
Water chesnut (Trapa natans)
This very distinctive floating rooted aquatic plant has a floating rosette of kite-shaped toothed leaves. Bladder-like swellings on their stems aid their floating. Submersed leaves are feathery and up to six inches long. Small white flowers give rise to large woody fruits with stout barbs, capable of impaling the feet of unsuspecting swimmers. Plants can also divide, quickly forming dense mats. Nutrient rich lakes and streams are most at risk.
> Photos and more info for this species.
HOW YOU CAN HELP: MONITORING & REPORTING
Wisconsin is a big place, with lots of places for weeds to grow... and hide. There are 54,300 square miles of forests, fields, wetlands, lakes, suburbs and cities. Of the state's 5 million residents, very few are familiar with local native trees, wildflowers and grasses -- or the invasive species that threaten them. Plus, seeds and plant parts are often small and easily dispersed by muddy shoes, tires treads, ATVs and boat trailers, or by birds, flowing water and even gardeners whose ornamentals escape into the wild. With so many potential routes and places of introduction for invasive plants, WDNR needs the help of citizens like you to prevent the spread of new invaders in wetlands and other natural habitats of the state.
> Read about how to become a Wisconsin Weed Watcher
> Read guidelines for collecting and reporting these invasive species
> Download Invasive Plant Reporting Form
REPORT THE FOLLOWING PLANTS IF FOUND ANYWHERE IN WISCONSIN
mile-a-minute
kudzu
Chinese yam
Japanese hops
giant hogweed
Japanese stilt grass
black or pale swallow-wort
European frog-bit
hydrilla
water chestnut
Brazilian waterweed
fanwort
parrot feather
REPORT THE FOLLOWING PLANTS IF FOUND IN THESE HABITATS
Japanese knotweed - shorelines
tree of heaven - forests and woodland edges
Japanese or spreading hedge parsley - Forests and woodland edges
flowering rush - wetlands, lakes, streams or shorelines
Voucher specimens or photos and location information for any of these plants should be sent to:
Invasive Plant Reporting
Endangered Resources Program, WDNR
101 S. Webster St.
Madison, WI 53707-7921
Or email information and photos to: kearns@dnr.state.wi.us
