Purple Loosestrife
Lythrum salicariaLythraceae
Whole Plant
Whole PlantFlowerStemStem
Photos (c) Cheryl Comeau Beaton unless otherwise noted


  • Purple lythrum, Rainbow weed, Spiked loosestrife

The Plant:

  • An erect perennial herb, branching at the top, 1.5-8 feet tall.

The Leaves:

  • opposite
  • sometimes whorled
  • entire
  • lance-shaped
  • smooth
  • somewhat clasping the stem

The Stem:

  • short, soft hairs
  • or without hairs
  • stiff
  • square or six-sided

The Flowers:

  • Purple-magenta flowers, .5 to .75 inches wide, typically with five petals, sometimes six or seven. Flowers have long petals and a greenish calyx, and grow in circles around the stem in a dense, clustered spike.

The Fruits:

  • dry capsule
  • green-brown

The Habitat:

  • wetlands, swamps, wet meadows
  • roadside ditches
  • shores of streams, rivers, lakes


  • fruits fall to the ground when ripe, or are dispersed by water or animals

Key ID Features:

  • opposite or whorled
  • lance-like leaves
  • 5 or 6 petals
  • purple-magenta
  • square stem

Similar Species:

  • Winged loosestrife (Lythrum alatum) is a rare native plant that resembles Purple Loosestrife, but is usually shorter (1-2.5 feet tall), has alternately arranged leaves except near the base of the plant, and has solitary flowers found in the upper leaf axils.


  • Purple Loosestrife is a very problematic plant that can take over wetland areas, dramatically reducing biodiversity. It also causes commercial, recreational and economic problems by clogging waterways. Manual removal is difficult due to the thick, almost woody rhizome, but can be effective. Removing blooms will help reduce the spread of seed to other areas.

Growth Form: Herb

Origin: Central Europe, Southern Europe, Great Britain, Russia

Level of Invasiveness for Nantucket: Invasive

Level of Invasiveness for Massachusetts: Invasive

Massachusetts Cultivation Restrictions: importation ban, propagation ban

Credits: The Electronic Field Guide to the Invasive Plants of Nantucket (c) 2005-2006 Maria Mitchell Association, EFG Project, UMass Boston