Habitat, Spread and Impacts

Habitat

Purple loosestrife grows in a wide range of soil textures and in both calcareous and slightly acidic soils. Outside of gardens, purple loosestrife grows in freshwater marshes, open stream margins, irrigation ditches, and alluvial flood plains. It has also been found in moist borrow pits along roads and in swamps along railroad tracks. In North America, it is invasive in habitats that support cattails (Typha spp.), reed canarygrass (Phalaris arundinacea), sedges (Carex spp.), rushes (Juncus spp.), willows (Salix spp.), common reed (Phragmites australis), and bulrushes (Scirpus spp.). Its growth and distribution are limited by cold temperatures and altitude.

Spread

Purple loosestrife is found throughout the Northern Hemisphere as far north as the 65th parallel and as far south as Italy in Europe. Immigrants to North America and across North America carried seeds for medicinal herb gardens and horticultural plantings. Seeds were carried in soil, often moist sand from tidal flats where purple loosestrife grew in Europe, used for ballast to balance loads in cargo ships. Seeds may have been intentionally introduced by beekeepers. Seeds are also believed to be transported by attaching to wool on sheep.

The seed containing capsules burst upon maturity facilitating short distance dispersal of seeds. In natural systems, seeds disperse long distances by floating in water currents and can be carried by waterfowl and wetland animals. The light seeds are also carried by wind. Adhesion to vehicles, boats, and boots may also disperse seeds. After mechanical disturbance, stems, root crowns, and root fragments can disperse by moving in water currents and initiate new populations. Draining of wetlands for agriculture and nutrient loading of waters is believed to have contributed to its colonization and spread.

Impacts

Studies indicate large-scale infestations can affect plant, animal, and water resources, and riparian/wetland community function. Purple loosestrife reduces wetland plant species richness and diversity. In competition experiments, purple loosestrife replaced cattail in shaded and full-sun conditions regardless of initial densities of each species. It similarly out-competed over 20 wetland plant species under variable nutrient levels and seasonal flooding within a few years. Forage production in wetland pastures is reduced by purple loosestrife infestations where livestock and wildlife only utilize young loosestrife plants prior to mid-June. The stems and roots are unpalatable to muskrats.

Many waterfowl species do not nest in dense stands of purple loosestrife including black terns, rails, grebes, and the least bittern. At the Montezuma National Wildlife Refuge in upstate New York, the disappearance of a population of 1,000 breeding pairs of black terns coincided with a population explosion of purple loosestrife. Purple loosestrife also affects water quality and wetland function. Its leaves have twice the phosphorous concentration of cattail leaves and decompose more rapidly resulting in a nutrient flush in the fall. Cattail and sedge leaves decompose in the winter and spring. The change in timing of phosphorous release may accelerate eutrophication downstream of infestations, and may jeopardize detritivore communities adapted to decomposition of plant tissues in spring. This could have negative affects on some fish populations.

Along with being valued as an ornamental plant, purple loosestrife has a long history of medicinal uses. The first century Greeks juiced the leaves to relieve mouth infections, used stems and flowers as a wound dressing, and believed it was affective against sleepwalking. The Romans used it as a red dye, as a dressing for foot sores, and thought it kept away snakes. More recently, the tannin-rich leaves were used to remedy diarrhea, dysentery, bleeding, wounds, ulcers, and sores. Bees use the nectar and pollen, and beekeepers have been implicated in its spread.

< Back to Ecology and Management of Purple Loosestrife (Lythrum salicaria L.)

Last Modified: 08/12/2008