Purple Loosestrife
Lythrum salicaria

Origin: Europe and Asia

Background: Purple loosestrife was introduced to the northeastern United States and Canada in the early 1800s for medicinal and ornamental uses.  Since then, it has spread rapidly and is now found in every U.S. state except Florida .  Residents often plant loosestrife and its cultivars in flower gardens, promoting the spread of the species.

Purple loosestrife is classified by New York State as one of three wetland plants that is a non-native aquatic invasive species.  Unfortunately, purple loosestrife remains a popular perennial for sale at Long Island nurseries.  The sale of purple loosestrife is banned in twenty states, including Massachusetts, Illinois, Minnesota,Wisconsin, Missouri, Iowa and Nebraska.

Habitat: Purple loosestrife has one major requirement for growth—moisture.  It is capable of invading many different types of wetlands, including wet freshwater meadows, tidal and non-tidal marshes, riverbanks, pond edges, reservoirs, and ditches.  It is particularly common invading road sides; its purple flowers are pervasive along upstate New York roadways.  Purple loosestrife can grow in water up to 18 inches deep. 

Ecological Threat: Purple loosestrife and its cultivars out-compete native marsh plant communities, replacing these vibrant areas with dense, homogenous stands.  Dense stands of purple loosestrife provide little in the way of food and habitat for native wetland wildlife including waterfowl, mink, muskrats, and amphibians.  This plant likely negatively affects our native fauna in other ways too - scientists recently found that purple loosestrife exudes chemicals that are toxic to American toad tadpoles.

The wild success of L. salicaria as a worldwide invasive is the result of a combination of qualities that allow it to thrive and expand its territory.  Purple loosestrife has an elaborate means of reproduction, copious seed production (a single plant can produce an estimated two to three million seeds per year), and a wide variety of dispersal mechanisms.  In addition to these advantages, loosestrife can adapt to changes in its immediate environment.  For example, it can change leaf morphology according to light levels.  This ability to adjust to a wide range of seasonal variations gives loosestrife a competitive advantage over other plants growing in the same area.

Peconic Estuary Distribution:  Several stands of purple loosestrife have been confirmed in Eastern Long Island , but limited information is available on the extent of invasions in the Peconics.

Description and Biology:

Identification: Purple loosestrife is most easily identified during the summer, its season of bloom.  Although there are several look-a-like species, purple loosestrife can be positively identified through differences in color and flower structure.  Loosestrife is the only reddish-purple flowered plant that develops monotypic stands over large wetland tracts, which often makes it easy to identify.  In early autumn, loosestrife leaves dehydrate and turn bright red—this color may last for up to ten days.  Dead stalks remain in place throughout the winter and are characterized by a unique brown tone as well as spire-shaped capsule clusters.

Prevention: Avoiding the purchase and planting of purple loosestrife is the best step to staving off potential invasions of this plant. Even purple loosestrife touted as “infertile” should not be planted since it can spread through underground stems as mentioned above at a rate of one foot per year.

Control:

Native Alternatives: Blazing star or gayfeather (Liatris spicata)