Exotic Plants of Illinois

Exotic Plants of Illinois Hong Qian, ISM Associate Curator of Botany and Ben L. Dolbeare, Natural Heritage, Illinois Department of Natural Recources, Springfield

Exotic species are those introduced through human activities to geographical regions where they were historically absent. Once established, many exotic species expand their geographical ranges within the region of introduction, and become invasive species. Such biological invasions have received increasing attention because biological invasions are among the most significant threats to biodiversity; they pose a significant threat to individual species as well as being responsible for major changes to ecosystem structure and functioning. Over 4000 exotic vascular plant species from around the world have been naturalized in the US, several hundreds of which are invasive species. They often get started in areas disturbed by human activities. Increasing concerns have been recently expressed that exotic species are invading natural areas. Invasive species cost the US more than $137 billion each year in biological control programs and lost agricultural revenues. Invasive plants usually reproduce rapidly. They can form stands that exclude almost all other plants, and thus change basic ecosystem processes. Invasive trees such as Norway maple (Acer platanoides) and vines like Japanese honeysuckle (Lonicera japonica) grow

into the canopy of a forest and shade out trees. Invasive shrubs such as bush honeysuckles (Lonicera maackii, Lonicera morrowii, and Lonicera tatarica) and buckthorns (such as Rhamnus cathartica, Rhamnus alnus, and Rhamnus davurica) take over the shrub storey while invasive herbs such as garlic mustard (Alliaria petiolata) dominate the herb layer of a forest. Within the US, Illinois is one of the states which hosts the largest numbers of exotic plant species. Of approximately 3250 species of vascular plants known within the state, approximately 1000 are exotic. In other words, approximately 27% of Illinois plant species are exotic. These exotic species are widely distributed across Illinois, and they are often invasive, quickly spreading through the countryside and causing both environmental and economic damage. Every county in Illinois has been invaded by exotic plant species (see Map). Hotspots of exotic species in Illinois, those counties indicated by red dots in the map, are often located in areas with a high human population and major universities. Some invasive species appear in all 102 counties of Illinois (see Table). The spreading of invasive species, largely due to human activity, causes the

biological homogenization of the Earth’s biota. This homogenization is recognized as a major factor in global change. Because globalization is progressing rapidly, threats to global biodiversity and economy posed by biological invasions will likely continue or accelerate.

WINTERCREEPER (EUONYMUS FORTUNEI) Wintercreeper, a vining shrub with opposite, leathery leaves, was introduced in 1907 from Asia as an ornamental ground cover plant. Tolerant of heavy shade, wintercreeper climbs trees and grows across the ground, smothering out native wildflowers and trees in forests and forest gaps. Flowers and fruits tend to be produced by the climbing vines with the seeds being dispersed by birds and other wildlife. Wintercreeper invades forests throughout the eastern United States; it is a serious invader in a number of Illinois woodlands where it has covered the ground and eliminated the native wildflowers of the area. It appears to be aggressive enough, if it is not eradicated, to also kill some of the trees.

THE LIVING MUSEUM › VOLUME 70 › NUMBER 1 › 2008

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COMMON TEASEL AND CUT-LEAVED TEASEL (DIPSACUS SYLVESTRIS) AND (DIPSACUS LACINIATUS)

SAWTOOTH OAK (QUERCUS ACUTISSIMA) This native of Asia was first introduced into the United States in 1862; however, it only recently has become widespread as wildlife biologists have recommended it for restoration projects and more recently it has been used as a landscaping tree throughout Illinois. Viable acorns are produced around 5 years after sprouting and its wide tolerance of environmental conditions gives it great potential to replace native trees such as native oaks in Illinois’ woodlands.

The teasels were introduced to North America from Eurasia and northern Africa in the 1700s, at which time the fruiting heads were used to comb wool. Now, teasels are popular in dried flower arrangements and horticultural plantings. Teasel will quickly form monocultures in disturbed parts of natural areas; along the interstates of Illinois, they are very damaging to roadside mowers. In fact, they and Phragmites are the major weed pests IDOT faces along much of Illinois’ interstates.

PHRAGMITES (PHRAGMITES AUSTRALIS) Phragmites, or common reed, is a tall perennial grass that can grow to heights of 15 feet or more. It grows abundantly in wet areas throughout Illinois and can persist for years after the area has dried up. The native and the exotic strains have hybridized to the extent that it is often very difficult to distinguish between the two. The native strains are generally more scattered, while the exotic strains form dome-shaped, dense masses. Growth in waterways is often so abundant as to clog the waterway and increase the chances of flooding. The exotic strains easily tolerate brackish water, giving them a competitive advantage for growth along interstates where salt is used to clear the roadways of snow and ice. 4


CROWN VETCH (CORONILLA VARIA) Crown vetch, native to Europe, Asia, and Africa, has been widely planted as a ground cover for erosion control, particularly along overpasses of interstate highways throughout Illinois, where it produces eye-catching white and pink to lavender cloverlike flowers. Crown vetch spreads prolifically, as it seeds easily and has creeping roots; it will grow over native vegetation, shading it out and thereby killing it. One of the problems with crown vetch is that it does not help in erosion control as originally thought as the soil is totally barren beneath the spread out plants, thereby increasing the odds of soil erosion.

LEAFY SPURGE (EUPHORBIA ESULA)

JAPANESE HOP (HUMULUS JAPONICUS) Japanese hop was introduced from eastern Asia as an ornamental in the mid 1800s and has since become established in disturbed areas, old fields, along roadsides, and in most floodplains throughout the eastern half of the United States. It grows over and smothers many native plants with its rapid growth. The pollen causes allergies in many people even though it is used medicinally in Asia. It does not contain compounds valued by brewers.

Native to Europe, leafy spurge was first found in the United States in 1827 and is thought to have been introduced several times accidentally in shipments of seeds and in ship ballast. Gardeners may have spread the plant for the beauty of its yellow ornamental bracts. Leafy spurge is an erect, perennial herbaceous plant that grows from 2 to 3.5 feet tall. It displaces native plants and reduces community diversity in natural areas throughout the northern half of Illinois; the roots exude chemicals that prevent the growth of other plants. It also invades pastures; unfortunately, cattle and horses can be poisoned from consuming these plants with their milky sap. Control of leafy spurge is the main concern of the Lake/McHenry Counties Cooperative Weed Management Area (CWMA).


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MUSK THISTLE (CARDUUS NUTANS) Musk thistle, a noxious weed in Illinois and native to Europe, Asia, and Africa, was accidentally introduced into the United States in the early 1900s. A rare plant in Illinois as recently as the 1960s, this spiny plant invades a variety of disturbed areas. Once established, it can spread rapidly due to high seed production (up to 11,000 seeds per plant) and form very dense stands, up to 60,000 plants per acre, reducing the available forage for stock in pastures and rangelands as it is far too spiny for consumption by cattle or horses. It also inhibits the growth of competing plants by releasing chemicals into the surrounding soil.

JAPANESE STILT GRASS (MICROSTEGIUM VININEUM)

Japanese stilt grass is native to Asia and was accidentally introduced into North America about 1920. It can monopolize the ground level plant community within 5 years of invading a natural area, at the expense of native grasses and wildflowers. It is a prolific seed producer and also spreads by rooting at the stem nodes. Few animals, including deer, actually browse this grass; however, overgrazing of native grasses by large populations of deer provides Japanese stilt grass with a great opportunity for invasion. It does provide excellent habitat for rats, which in turn prey upon ground nesting birds’ eggs. This grass has traditionally been used in the packing of oriental porcelain, possibly explaining its accidental introduction. Japanese stilt grass has since spread into the southern third of Illinois and is a new emerging invasive plant problem in natural areas.

GIANT HOGWEED (HERACLEUM MANTEGAZZIANUM)

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Giant hogweed with its small white flowers clustered in a broad head resembles a giant carrot in flower; however, this biennial, herbaceous plant reaches heights of around 15 feet. Unlike carrot, giant hogweed is of serious concern for human health. When its sap gets on the skin and is exposed to sunlight, humans experience painful burning and blistering; such blistering often gives way to purple or black scars, which may last for several years. Either temporary or permanent loss of vision with humans can also occur if the sap is permitted to enter into the eyes. Giant hogweed, native to Europe and Asia, was first introduced into the United States in 1917 for ornamental purposes. It was discovered in Illinois during the summer of 2007, and all four populations were eradicated. THE LIVING MUSEUM › VOLUME 70 › NUMBER 1 › 2008

MULTIFLORA ROSE (ROSA MULTIFLORA) BIRD’S-FOOT TREFOIL (LOTUS CORNICULATUS) This legume with its pretty and showy yellow flowers is a highly nutritious and delicious forage plant for cattle. It was introduced from Europe into the United States in the early 1800s for cultivation in pastures for hay and it easily escapes cultivation. It is also used for erosion control along highways, but its value for this purpose is questionable. Birds-foot trefoil forms dense mats, shading out all other plants. This is of concern where prescribed burns are used to maintain prairies, as birds-foot trefoil will often move in and out-compete the native prairie plants.

Multiflora rose is a multi-stemmed, thorny shrub that grows up to 15 feet tall. It was introduced into eastern United States from Japan in 1866 as a rootstock for ornamental roses. Its use for erosion control, as a plant for living fences and wildlife cover, was promoted in the mid 1900s throughout the Midwest by both state and federal agencies. It is still planted by the highway departments in several states as a snow fence and a soft but effective crash barrier in highway medians. The arching canes with their stout thorns form thickets impenetrable to humans and most animals. A single plant can produce over a million seeds per year, which are often eaten and spread by various birds and other wildlife. In Illinois, multiflora rose invades prairies, old fields, pasture lands, forest edges, and open areas in woodlands.

AUTUMN OLIVE AND RUSSIAN OLIVE (ELAEAGNUS UMBELLATA) AND (ELAEAGNUS ANGUSTIFOLIA) Autumn olive, native to China, Korea and Japan, was introduced to the United States in 1830; Russian olive, native to southeastern Europe and western Asia, was introduced into the United States in the late 1800s . Both species have been widely planted for strip mine reclamation, windbreaks, and for screening and bank stabilization along roadways because of their tolerance to salt. Once established, these two highly invasive and aggressive species can eliminate almost all other plants from the area. Thickets of either of these two species are nearly impenetrable by humans and other animals.


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HUNNYSUCKLES: AMUR HONEYSUCKLE (LONICERA MAACKII), MORROW’S HONEYSUCKLE (LONICERA MORROWII), AND TARTARIAN HONEYSUCKLE (LONICERA TATARICA) These honeysuckles are multi-stemmed, upright deciduous shrubs up to 30 feet tall. The first bush honeysuckle introduction from Eurasia into the United States was in 1752 and most of these exotic honeysuckles are now well established in the woodlands of Illinois. Early on, the US Department of Agriculture promoted honeysuckle for wildlife, and commercial nurseries sold it as an ornamental because of its attractive flowers and brightly colored fruit. These exotic honeysuckles leaf out earlier in the spring and hold their leaves later in the fall than most native shrubs, giving them greater competitive ability than their native counterparts. Many of the birds using these exotic honeysuckles for nesting habitat experience greater nest predation, as the birds build their nests closer to the ground in honeysuckle thickets than they would if they used native shrubs. These aggressive shrubs will totally replace the native shrubs and wildflowers if not properly managed in Illinois woodlands.

JAPANESE HONEYSUCKLE (LONICERA JAPONICA) Japanese honeysuckle, native to eastern Asia, is an evergreen to semievergreen vine that can be found either trailing or climbing to heights of over 80 feet. It was introduced into the United States in 1806 as a landscape plant. It forms dense blankets over trees, shrubs and wildflowers throughout the southern third of Illinois where it is widely established. Excessive vining in trees and shrubs makes them vulnerable to wind and ice damage; in some cases, it has girdled and killed mature trees. The value to wildlife is minimal since Japanese honeysuckle usually forms a monoculture.

BURNING BUSH OR WINGED EUONYMUS (EUONYMUS ALATUS) Burning bush, so named for its brilliant red fall foliage, is a deciduous shrub that grows up to 20 feet tall. It was introduced into the United States in the 1860s as an ornamental plant from Asia. Many cultivars have been developed and are used in landscaping. Once established, it can form dense thickets that displace native vegetation. This plant has become invasive in the eastern United States, including southern Illinois. Birds readily eat the fruits and spread the seeds. 8


BUCKTHORNS: COMMON BUCKTHORN (RHAMNUS CATHARTICA), GLOSSY BUCKTHORN (RHAMNUS FRANGULA), AND DAHURIAN BUCKTHORN (RHAMNUS DAVURICA) Buckthorns were introduced into North America for use in landscaping in the early 1800s. Buckthorns in northeast Illinois form dense thickets under which very few other plants receive enough light for healthy growth. They change the chemistry of the soil so as to encourage their growth and discourage the growth of native species. They also have an additional competitive advantage as, like the exotic honeysuckles, they leaf out earlier than native plants and hold their leaves later than native plants.

CALLERY PEAR (PYRUS CALLERYANA) Callery pear, also called Bradford pear, is an ornamental deciduous tree with some non-sterile cultivars that have escaped and are invading natural areas throughout the eastern United States. Callery pear colonizes disturbed woodlands, roadsides, cloverleafs, and old fields, forming dense, often thorny thickets as they crowd out native species. The trees are quite vulnerable to storm and ice damage and are short-lived; therefore, they are no longer recommended for landscaping by most nurseries in Illinois. Many of the cultivars are self-sterile; however, viable seeds will be produced when crossed with other cultivars.

EURASIAN WATER-MILFOIL (MYRIOPHYLLUM SPICATUM) Native to Europe, Asia, and North Africa, Eurasian water-milfoil is a submersed aquatic plant that invades lakes, ponds, and other aquatic environments throughout the United States. It probably came to North America in ballast water or for use in aquariums, and is a serious pest in several lakes of Illinois. It was first identified in the early 1940s although it is thought to have been present in North America since the late 1800s. Eurasian water-milfoil roots in water, usually reaching 3 to 10 feet in length. However, they can grow as long as 30 feet. Once established, it can form dense mats of leaves that restrict light availability to the water environment, resulting in a decline in the diversity and abundance of native plants and animals. Milfoil spreads mainly by autofragmentation, and fragments often become caught up with boats and trailers to be deposited in another lake distant from the original source. Swimming, boating, and fishing are often made impossible from these very dense milfoil mats.

PHOTOGRAPH CREDITS: Euonymus fortunei (James H. Miller, USDA Forest Service, Bugwood.org), Quercus acutissima (Chuck Bargeron, University of Georgia, Bugwood. org), Dipsacus laciniatus (Chris Evans, River to River CWMA, Bugwood.org), Phragmites australis (Leslie J. Mehrhoff, University of Connecticut, Bugwood.org), Humulus japonicus (John Randall), Euphorbia esula (William M. Ciesla, Forest Health Management International, Bugwood.org), Carduus nutans (John Randall), Heracleum mantegazzianum (Donna R. Ellis, University of Connecticut, Bugwood.org), Microstegium vinineum (Sylvan R. Kaufman), Lotus corniculatus (David Cappaert, Michigan State University, Bugwood.org), Rosa multiflora (James H. Miller, USDA Forest Service, Bugwood.org), Elaeagnus umbellate (Pennsylvania Department of Conservation and Natural Resources —Forestry Archive, Bugwood. org), Elaeagnus angustifolia (John Randall), Lonicera maackii (Chuck Bargeron, University of Georgia, Bugwood.org), Lonicera morrowii (Chris Evans, River to River CWMA, Bugwood.org), Lonicera tatarica (Patrick Breen, Oregon State University, Bugwood.org), Lonicera japonica (Chuck Bargeron, University of Georgia, Bugwood.org), Euonymus alatus (James H. Miller, USDA Forest Service, Bugwood.org), Rhamnus cathartica (Sylvan R. Kaufman), Pyrus calleryana (Chuck Bargeron, University of Georgia, Bugwood.org), Myriophyllum spicatum (Barry Rice/sarracenia. com), Alliaria petiolata (Chris Evans, River to River CWMA, Bugwood.org), Coronilla varia (Dan Tenaglia, Missouriplants.org retrieved from invasive.org). THE LIVING MUSEUM › VOLUME 70 › NUMBER 1 › 2008

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Exotic Species Found in All or Nearly All Counties of Illinois

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Scientific Name

Common Name

Achillea millefolium

common yarrow

Alium vineale

wild garlic

Bromus inermis

smooth brome

Bromus tectorum

cheatgrass

Capsella bursa-pastoris

shepherd’s purse

Cerastium vulgatum

big chickweed

Dactylis glomerata

orchardgrass

Daucus carota

Queen Anne’s lace

Digitaria sanguinalis

hairy crabgrass

Eragrostis cilianensis

stinkgrass

Festuca pratensis

meadow fescue

Lactuca serriola

prickly lettuce

Medicago lupulina

black medic

Medicago sativa

alfalfa

Melilotus albus

white sweetclover

Mlilotus officinalis

yellow sweeclover

Pastinaca sativa

wild parsnip

Phleum pratense

timothy

Plantago lanceolata

narrowleafplantain

Poa compressa

Canadian bluegrass

Poa pratensis

Kentucky bluegrass

Plygonum arenastrum

oval-leaf knotweed

Portulaca oleracea

little hogweed

Rumex acetosella

common sheep sorrel

Setaria faberi

Japanese bristlegrass

Setaria glauca

yellow foxtail

Setaria viridis

green bristlegrass

Stellaria media

common chickweed

Taraxacum officinale

common dandelion

Trifolium hybridum

alsike clover

Trifolium pratense

red clover

Trifolium repens

white clover

Verbascum thapsus

common mullein

Veronica arvensis

corn speedwell


FURTHER READING Elizabeth J. Czarapata. 2005. Invasive Plants of the Upper Midwest: An Illustrated Guide to their Distribution and Control. The University of Wisconsin Press. Hill, R., and S. Williams. 2007. Maine Field Guide to Invasive Aquatic Plants and their Common Native Look Alikes. MCIAP. www. mainevolunteerlakemonitors.org Invasive and Exotic Species. http://www.invasive. org/weeds.cfm. Kaufman, S. R. & W. Kaufman. 2007. Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species. Stackpole Books, Mechanicsburg, PA. Nature Conservancy. The Invasive Species Initiative Web page. Available online: tncweeds. ucdavis.edu. Randall, J. M. and J. Marinelli (eds). 1996. Invasive Plants: Weeds of the Global Garden. Brooklyn Botanic Garden.