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Invasive Species Identification Sheet - Purple Loosestrife

Purple Loosestrife (Lythrum salicaria L.)

  • herbaceous perennial with woody taproot that produces clusters of many stems 3'-10' tall
  • above-ground parts die back over Winter; dead stems may remain standing over Winter
  • stems stiff, square (or many-angled in mature plants); increasingly woody in late summer
  • stems end in a long, showy flower spike bearing many closely-attached flowers
  • flowers bright pink to dark purple, each with 5-7 petals
  • leaves opposite or whorled; without stalks; lance-shaped, with entire (untoothed) margins
  • leaves and stems sometimes have soft hairs
  • wetland invader; displaces open water and native plants of value to wildlife

Purple Loosestrife may be distinguished from other species of Lythrum by its stems that end in dense, showy flower spikes. The lance-shaped leaves are up to 4 inches long, and mostly opposite or in whorls of 3 (which may appear alternately arranged). Some leaf bases are heart-shaped and may clasp the main stem. On the main (angled) stem, young, new shoots bearing small leaves may angle out directly above mature leaves.

Purple Loosestrife grows in wet, open, sunny areas. Habitats include wet meadows or fields, stream and river banks, flood plains, ponds, lakes, tidal and non-tidal marshes and human-created habitat such as ditches. It can tolerate changing water depths. Purple Loosestrife spreads to new places from seeds carried by water, wind, animals, and people's shoes, boats, etc. It also can grow from transported stems or pieces of root.

Purple Loosestrife has been planted widely for its beauty. There are many horticultural varieties, all of which (contrary to popular opinion) are fertile and can spread seeds and/or pollen.