Purple loosestrife is a wetland perennial in the Lythraceae which was introduced to North America from Europe and Asia during the early 1800s as a contaminant of ship ballast. For about a century it existed as a pioneer species along the northeastern seaboard. Its range expanded inland in the 1880s with the construction of inland canals and waterways and further increased as the plant was developed as an ornamental and for bee forage. Purple loosestrife was found in the upper Midwest by the 1930s and now occurs from southern Canada throughout most of the temperate United States. Populations are heaviest in the glacial wetlands of the northeast, where it forms dense, monoculture stands which crowd out native vegetation, degrades wildlife habitat, and obstructs waterways. Numerous populations have been found in the midsouth area, including several in North Carolina.

Purple loosestrife grows up to 10 ft. tall and has a vigorous rootstock that stores carbohydrates for growth each spring and regrowth, if the plant has been cut. Plants grow best in moist soil in full sun, but they can survive in up to 50% shade. Older plants may have 30 to 50 stems, which form large tops and dominate the herbaceous canopy. The stems are pubescent, square in cross section, and woody at their bases. Stems die in the fall but remain standing through the winter. New stems grow from the root and rhizome system and produce dense stands within a few years of the initial invasion. The leaves are smooth, lance-shaped, and opposite (occasionally in whorls of three), up to 4 in. long, and are expanded at the base. Plants reproduce largely by seeds, but also may propagate from vegetative cuttings. Purple loosestrife has showy, attractive flowers with 5 to 7 purple petals occurring in dense, terminal spikes 6 to 8 in. long. The flowers bloom from June to September and are insect pollinated. One mature plant may produce as many as 3,000 flowers and 2.5 million minute, orange seeds, which are dispersed by largely wind from late summer through the winter. Seeds can survive periods of flooding as long as 20 months and may remain dormant in the soil for several years. Seedling densities can reach 12,000-24,000 plants/sq. yard.