Purple loosestrife invades and destroys habitat along rivers, streams, and wetlands. It grows in dense patches that choke out native plants and deter wildlife. Purple loosestrife is a prolific seed producer and its light seeds are carried by wind and often take hold in nearby wetlands.
Purple loosestrife was first reported in North America in the early 1800s. The mode of introduction is not certain, but it is possible that it was introduced via ballast water or as an ornamental. Since the initial introductions this plant is often shared by gardeners or spread in waterways. Purple loosestrife is a prolific seed producer and seeds may be disbursed long distance by waterfowl. Seeds may also "hitchhike" on imported sheep or raw wool.
Lythrum salicaria is an herbaceous wetland perennial that can grow 0.5-1.5 m tall. The leaves are normally opposite and in pairs, however they can be alternate and they can be found in whorls of three. Leaves are lance-shaped and 3-10 cm long. The flowers are purple to pink. They are numerous and borne on spikes that are between 10 and 40 cm long. Each flower has 5-7 petals. The flowers are in bloom from July to September. The fruits are capsules, each containing numerous reddish-brown seeds.