Aggressively invading Ontario’s wetland regions, purple loosestrife’s damage is beautiful, yet devastating. Although admittedly an aesthetically pleasing plant, its destructive and dominant nature has earned it a spot on Canada’s top-five invasive species list, making the flower a significant biological priority. This one- to two-metre tall “marsh monster” leaves a trail of destruction with serious consequences for the local environment—and we may already be unknowing accomplices.

Native to Eurasia, purple loosestrife (Lythrum salicaria, from the family Lythraceae) was introduced to North America from European ships in the 1800s as a medicinal herb, used to treat bleeding, ulcers, diarrhea, and dysentery.

Upon arrival, the plants spread quickly across Canada, populating their preferred habitat: freshwater lakes, river shores, and marshlands. As a result, dramatic growth of these purple-pink pests is causing water flow disruptions and drastic declines in biodiversity in many of Ontario’s wetlands.

Identified by its uniquely-shaped square stem, each purple loosestrife plant can produce as many as 30 rigid stalks from a central, woody root mass that grows 8.5 inches each year. Surrounded by clusters of leaves and ravishing pink and purple flowers, this weedy species makes for an attractive ornamental garden plant. Garden strains of purple loosestrife—commonly known as Morden Pink, Morden Gleam or Dropmore Purple—are usually sold in packets of wildflower seeds. Unwitting gardeners may grow this invasive species in backyards and contribute to its survival and spread.

Strains originally thought to be sterile may not be, according to recent scientific research. An experiment in Manitoba showed that after six months of cultivating the strain known as Morden Pink, each plant produced an abundance of “garden escape” seeds in ideal condition for germination.

Purple loosestrife has the remarkable ability to produce approximately three million small, light seeds that can be easily dispersed long distances by wind, rainfall, and wildlife. Both rural and urban settings also provide pollination by bees and butterflies.

Growth of purple loosestrife has caused far-reaching ecological damage in the wetlands of southern Ontario. The loss of native flora and fauna through competition, and the reduction of natural food and protective habitats for wildlife results in the disappearance of a variety of rare animal and plant species, many of which play critical roles in maintaining wetland ecosystems.

Many researchers are looking into control and preventive measures to eradicate the growth of this obnoxious weed. Some suggest that hand-removal and proper disposal of purple loosestrife from gardens is a helpful strategy. The approved release of four natural purple loosestrife predators may help. Two beetles (Galerucella calmariensis and Galerucella pusilla), a seed weevil, (Nanophyes marmoratus) and a root weevil, (Hylobius transversovittatus) feed on the purple loosestrife plant while posing no known threat to other species.

Despite these measures, purple loosestrife continues to remain a number-one threat to Ontario’s wetland habitats.