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Purple loosestrife

Quick facts

Purple loosestrife is a prohibited invasive species. It is illegal to possess, import, purchase, transport, or introduce these species (including hybrids or cultivars) except under a permit or statutory exemption. Transport directly to the Minnesota Department of Natural Resources in a sealed container for identification or reporting purposes is permitted.

  • Purple loosestrife can invade many wetland types including wet meadows, stream banks, pond or lake edges and ditches. 

  • Populations can expand quickly and form dense stands that crowd out native vegetation.

  • Purple loosestrife should be reported. 

See the Minnesota Department of Natural Resources recommendations for reporting invasive species.

How to identify purple loosestrife

  • Perennial herbaceous plant with bushy appearance.

  • Can grow three to seven feet tall and will have multiple stems growing from a single rootstock.

Stem

  • Stiff, typically square shaped.

  • Can have up to six sides, often branching.

Leaves

  • Opposite or whorled.

  • Lance shaped with smooth edges

  • Stalkless.

  • Can be downy.

Flowers

  • Purple-pink flowers bloom in tall spikes for most of the summer months.

  • Multiple rings of flowers bloom at once from the bottom of the spike to the top.

  • Flowers typically have six petals.

Seeds

  • Tiny, with up to 300,000 seeds produced per stem each year.

  • Seeds are viable for up to 20 years.

Roots

  • Large, woody taproot with rapidly extending, fibrous rhizomes.  

Purple loosestrife stem
Purple loosestrife flower

 

Angela Gupta, Extension educator; Amy Rager, Extension educator; Megan M. Weber, Extension educator

Reviewed in 2019

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