Natural History
Geographical Origin and History
Purple loosestrife is a perennial plant native to Europe and some parts of Asia. It was first reported in North America along the eastern seaboard in 1814. The original introductions occurred in the early 1800's via plants brought by settlers and seeds carried within livestock and soil used for ship ballast. Once in North America, purple loosestrife quickly spread westward displacing native wetland plant communities. Purple loosestrife can now be found growing throughout most of North America. Due to its attractive flowerheads, purple loosestrife is often used as a garden flower. Several states now ban the sale and possession of this plant.
Characteristics
Purple loosestrife can germinate in moist, exposed soils at wide range of pH, nutrient, and light levels. Once established, seedlings can survive shallow flooding. The plant develops an impressive rootcrown and dense shoots that out-compete adjacent plant life. The stalks are square and commonly attain heights up to 2m on mature plants. The leaves are opposite each other and alternate at 90 degree angles along the stem. The distinctive flowering spike of purple loosestrife blooms from mid July through early September in the upper Great Lakes region.
Reproduction and Dispersal
Mature plants can produce over 2 million seeds annually. The tiny seeds are lightweight and are easily dispersed by both wind and water currents. Wildlife can minimally spread seeds stuck to their feet and legs. Humans carry seeds and plant fragments from one site to the next on clothing and equipment. Seeds may lie dormant for years until conditions become suitable for germination. The most common vectors for the spread of purple loosestrife include roadside ditches, riparian shorelines, and boat landings where moist exposed soils and frequent traffic or disturbances create optimal germination conditions.
Habitat Preference and Tolerance
Although purple loosestrife prefers rich, organic soils, it will grow in most substrates, including clay, sand, muck, and silt. Plants can survive in partial shade, but full sunlight is preferred. Optimal habitat includes marshes, stream banks, flood plains, and wet meadows and prairies. Purple loosestrife can also thrive as a lawn and garden ornamental (a common method of introduction into nearby natural habitats). Populations flourish in wetlands that have been disturbed or degraded through both natural and man-made processes. Banks and mudflats exposed following a drawdown are highly susceptible if a seed source is present.