Introduction

Purple loosestrife (Lythrum salicaria) is a wetland plant from Europe and Asia.  It was introduced into the east coast of North America in the 1800s. First spreading along roads, canals, and drainage ditches, then later distributed as an ornamental garden plant, this exotic plant species is in 40 states, Iowa included, and in all Canadian border providences.

Purple loosestrife invades marshes and lakeshores, replacing cattails and other wetland plants. In some locations, natural cattail marshes have been completely overtaken by loosestrife. The plant forms dense, impenetrable stands that are unsuitable as cover, food, or nesting sites for a wide range of native wetland animals including ducks, geese, rails, bitterns, muskrats, frogs, toads, and turtles. Many rare and endangered wetlands plants and animals are also at risk.

Purple loosestrife thrives on disturbed, moist soils, often invading after some type of construction activity. Eradicating an established stand is difficult because of the enormous number of seeds the plant produces, often over 2 million seeds from a single adult plant annually. The plant is also able to resprout from its extensive underground root network, and from broken stems that fall onto the ground or in the water.

A major reason for purple loosestrife's expansion is a lack of effective predators in North America. Several European insects that attack only purple loosestrife are being tested as a possible long-term biological control of the plant in North America.

In Iowa, the plant has spread along the Mississippi River, but it has been controled fairly effectively in inland marshes and waterways. The Iowa Department of Natural Resources has spent a lot of time and money to keep purple loosestrife out of wildlife and waterfowl habitat areas.

Description

Purple loosestrife is an herbaceous perennial characterized by long showy spikes of magenta flowers. Usually under 4 feet in height, the plant may reach up to 10 feet tall in nutrient-rich habitats. Purple loosestrife has flowers with 5 to 7 petals which occur in dense clusters on terminal spikes and which bloom from June to September. The leaves are usually opposite or in whorls of 3, lance-shaped, and without teeth. The plant is a member of the loosestrife family (Lythraceae) and may be confused with other members of that family, particularly with the native winged loosestrife (Lythrum alatum), which is rare in Virginia. Winged loosestrife, however, is generally smaller in height, averaging about 2 feet, has alternate leaves on the upper portion of the stem, and has fewer, more widely-spaced flowers. Purple loosestrife is virtually indistinguishable from another Eurasian species, Lythrum virgatum, and its cultivars.

Habitat requirements:

Loosestrife tolerates a wide range of environmental conditions. It favors fluctuating water levels and other conditions often associated with disturbed sites. It is shade intolerant and is apparently unable to invade saline wetlands. Reed canary grass and Japanese millet will compete with loosestrife.

Likely means of spread:

Seeds escape from gardens and nurseries into wetlands, lakes, and rivers. Once in aquatic systems, seeds are easily spread by moving water and wetland animals.