Purple Loosestrife, Lythrum salicaria

Purple loosestrife is a pretty, purple-flowered plant that was brought to the United States from wetlands areas in Europe in the early 1800's, most likely because of its ornamental value. Although it is very attractive, this plant is deadly to American wetlands because it crowds out the native plants that support bird and animal populations in marshy areas. Purple loosestrife, also known as the purple plague, got its American start in New England. From there, it spread rapidly north into Canada, south into Virginia, and west through the States bordering the Great Lakes. Currently, it can be found throughout the United States and is menacing the wetlands in the Northeast and upper Midwest.

Purple loosestrife is a big, long-lived perennial (life cycle lasting longer than 2 years) that can grow almost 6 feet (2 m) tall. Its square, tough stems grow in a cluster and support lance-shaped leaves about 3 inches (8 cm) long. At the top of the stems are flowers ranging in color from deep purple to bright magenta.

Each mature plant produces more than a million seeds that can be carried by wind and water. Adult plants can also regrow from just roots or pieces of stems. These qualities make purple loosestrife a terrific reproducer.

This plant is used for landscaping in some States because of the beauty of its flowers. Purple loosestrife is also used by beekeepers because of its sweet nectar. Currently, purple loosestrife is listed as a noxious weed by about 2 dozen States. This means that the plant cannot be brought into those States or sold in nurseries there.

Unfortunately, researchers have not found any species of wildlife that can make use of loosestrife. Once it starts to grow in the wild, it displaces native plants that are useful to wildlife. The fact that purple loosestrife is a long-lasting perennial and can produce so many seeds makes it a serious threat to wetlands in the United States. It can take over areas such as lakeshores, streambanks, and marshes and then outpace most native plants, including some species of endangered orchids. After only a few summers, fields of the purple plague can grow to thousands of acres, virtually eliminating marsh and wetland habitats with its dense clusters of stems.