Purple loosestrife (Lythrum salicaria)isan aggressive wetland plant species first introduced into the United States from Europe. It is a showy, attractive plant that grows up to 4 feet (1.2 m) in height with pink and purple flowers arranged on a spike, and it is common in shallow marshes and lakeshores all across the northern half of the United States.

Loosestrife is a perennial plant species that spreads rapidly because of the high quantity of seeds it produces (sometimes up to 300,000 seeds per plant) and the efficient dispersal of seeds by wind and water. The plant has a well-developed root system and is able to tolerate a variety of soil moisture conditions. This has made it an effective colonizer of disturbed ground as well as areas with fluctuating hydrological regimes. Because of its attractive flowers, it has also been planted as an ornamental species.

Purple loosestrife (Lythrum salicaria...