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  Purple loosestrife  

Department of Natural Resources

Illinois Exotic Species:
purple loosestrife Lythrum salicaria

Purple loosestrife is an herbaceous perennial that may attain a height of two to seven feet. Its leaves are arranged opposite each other along the stem. Leaves are sessile. The small, purple flowers are borne at the tip of a stiff, four-sided stem. Flowers contain five or six petals. Flowering in Illinois occurs from June through August. The fruit produced is a capsule. Purple loosestrife is a native of Europe and Asia. It was introduced to the east coast of North America in the early 1800s by immigrants as an ornamental and herb, and accidentally through seeds in the ballast of ships and the wool of sheep. Transport of seeds from these plants has allowed purple loosestrife to escape into other areas. It spread into the Midwest in the 1880s and reached Illinois in the 1940s or 1950s. Most Illinois populations are in Kane, Lake, McHenry, Cook, DuPage and Carroll counties, although it has been found in many other areas in Illinois. Purple loosestrife invades moist areas and shallow water, making conditions unfavorable for the growth of native wetland plants. The dense clusters of purple loosestrife plants form areas which are unsuitable for cover, food or nest sites for a variety of wetland species. Purple loosestrife often becomes invasive after a disturbance, such as construction or lowering the water level in a lake. Eradication of this species is difficult due to the tremendous numbers of its seeds. Each plant can produce thousands of seeds per year, and seeds may lay dormant in the soil for many years. It can also reproduce from roots and broken stems. Purple loosestrife has no native predators in North America. Attempts at slowing or stopping its spread by using herbicides, pulling and burning have been unsuccessful. A biological control method is now being attempted. Two beetle species have been imported from Europe, propagated and released in areas of heavy loosestrife infestation. These beetles feed only on purple loosestrife. Results have been promising, with the beetles able to consume large quantities of the loosestrife plants.

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