The invasion of natural habitats by non-native or exotic plants poses a serious threat to Illinois natural ecosystems, second only to habitat destruction in importance. The harm these weeds inflict on landscapes ranges from being direct pests of forests, prairies, and wetlands to highly competitive invaders capable of displacing native species. 

WETLANDS
Eurasian Watermilfoil (Myriophyllum spicatum)
Purple Loosetrife (Lythrum salicaria)
Hydrilla (Hydrilla verticillata)
Alligator Weed (Alternanthera philoxeroides)
Watercress (Rorippa nasturtium-aquaticum, syn. Nasturtium officinale)
Water Hyacinth (Eichhornia crassipes)
Brazilian Elodea (Egeria densa)
Flowering Rush (Butomus umbellatus)
Reed Canary Grass (Phalaris arundinacea)
Curly Pondweed (Potamogeton crispis)

GRASSLANDS
Crown Vetch (Coronilla varia)
Multiflora Rose (Rosa multiflora
Teasel (Common Teasel: Dipsacus syvestris & Cut-leaved Teasal: Dipsacus laciniatus
Sweet Clover (Yellow Sweet Clover: Melilotus officinalis & White Sweet Clover: Melilotus alba
Spotted Knapweed (Centaurea stoebe ssp. Micranthos)
Common Reed Grass (Phragmites australis, syn. P. communis)
Leafy Spurge (Euphorbia esula)
Giant Hogweed (Heracleum mantegazzianum)
Bicolor Lespedeza (Lespedeza bicolor)
Chinese Lespedeza (Lespedeza cuneata)

WOODLANDS 
Amur Honeysuckle (Lonicera maackii)
Tatarian Honeysuckle (Lonicera tatarica)
Japanese Honeysuckle (Lonicera japonica)
Kudzu (Pueraria montana var. lobata)
Tree-of-Heaven (Ailanthus altissima)
Russian & Autumn Olive (Russian: Elaeagnus angustifolia & Autumn: Elaeagnus umbellata)
European Buckthorn (Rhamnus cathartica)
Garlic Mustard (Alliaria petiolata)
Japanese Knotweed (Polygonum cuspidatum syn. Fallopia japonica)
Wild Parsnip (Pastinaca sativa)
Oriental Bittersweet (Celastrus orbiculatus)
Chinese Yam/Cinnamon Vine (Dioscorea oppositifolia)
Chocolate Vine/Five Leaf Akebia (Akebia quinata)

AGRONOMIC 
Common Dayflower (Commelina communis)
Star of Bethlehem (Ornithogalum umbellatum)
Poison Hemlock (Conium maculatum)
Maiden Grass (Miscanthus sinensis)
White Campion (silene latifolia subsp. alba)
Bur Cucumber (Sicyos angulatus)
Mile-a-Minute Vine (Polygonum perfoliatum)
Japanese Hop (Humulus japonicus)