Purple Loosestrife

Fact SheetLythrum salicaria

Invader Images

    • Purple loosestrife
    • Purple loosestrife fruit
    • Purple loosestrife infestation
    • Purple loosestrife flower
    • Purple loosestrife

Common Look-alikes

    • narrow-leaved fireweed
      Narrow-leaved fireweed flowers have four petals and leaves are alternately arranged

Identification

Appearance

Lythrum salicaria is a tall, multistemmed (30-50 per plant), perennial forb that can grow up to 5 ft. in height.

Foliage

The opposite or whorled leaves are dark-green, lance-shaped, sessile, 1.5-4 in. (3.8-10.2 cm) long and round or heart-shaped at the base.

Flowers

Flowering occurs in July to October, when pink to purplish flowers develop in 4-16 in. (10.2-40.6 cm) long spikes at the tops of the stems. Flowers have 5-7 petals and twice as many stamens as petals.

Fruit

Fruits are capsules that are enclosed in the hairy sepals and contain several reddish brown seeds.

Biology

This species is Quarantined: Class B Noxious Weed

Origin 

Purple loosestrife is native to Europe and Asia. It was first introduced into North America in the early 1800s for ornamental and medicinal purposes.

Habitat 

Purple loosestrife grows in a variety of wet habitats, including wet meadows, marshes, river banks, and the edges of ponds and reservoirs. It tolerates a wide variety of moisture, nutrient, and pH conditions.

Threat 

Purple loosestrife can quickly form dense stands that completely dominate the area excluding native vegetation. This plant can spread very rapidly due to its prolific seed production; each plant can produce up to 2.5 million seeds per year. It can also hybridize with native loosestrife species, potentially depleting the native species gene pool.

Loosestrife invades both natural and disturbed wetlands and alters their ecological structure and function.

Life Cycle 

This aggressive plant spreads both vegetatively and by abundant seed dispersal.

With an extended flowering season, and an unusually high number of flowering stems, each purple loosestrife plant is capable of producing two to three million seeds per year. Research has shown that cultivars, advertised as sterile, are capable of producing viable seed. This plant can also reproduce vegetatively by underground stems at a rate of one foot per year.

Management Options

Mechanical

Hand-pulling is only effective for seedlings with small roots. Mowing is not recommended, but may reduce the production of seeds. Flooding kills seedlings; established plants must be inundated for weeks. Unfortunately, this also kills desirable vegetation. The site may need to be replanted with native, competitive vegetation.

Chemical

 Glyphosate is effective against purple loosestrife. Be sure to use an herbicide permitted for wetland use. Herbicides can be applied directly to cut stems to reduce collateral damage.

Biocontrol

Although they will not eradicate purple loosestrife, biocontrols can reduce the severity of an infestation. Four species of beetles from Europe, which are fairly host-specific on purple loosestrife, are currently available for control efforts.

**Be careful not to damage or kill nearby native plants when conducting management work. And when using herbicides, always follow the instructions on the label.**

Citations

photo credit

Purple loosestrife1, 5535247, Richard Gardner, UMES, Bugwood.org

Purple loosestrife2, 5479559, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Flower, 5530447, Becca MacDonald, Sault College, Bugwood.org

Fruit, 5479532, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Infestation, 5488974, Eric Coombs, Oregon Department of Agriculture, Bugwood.org

Narrow-leaved fireweed, 5356530, Terry L Spivey, Terry Spivey Photography, Bugwood.org

information credit

Adirondak Park Invasive Plant Program

Center for Invasive Species and Ecosystem Health

Go Botony 

Pennsylvania Department of Conservation and Natural Resources