Stem: The erect stem is usually square in cross-section, 0.5-2 m tall, and often branched. May be covered with fine whitish hairs.

Flower: Showy purple-pink flowers occur in erect spikes at the stem tops. The stalkless flowers have 5 sepals and 5-7 delicate wrinkled petals (7-14 mm long).

Fruit: Egg-shaped capsule (3-4 mm) has many tiny seeds. A single plant may produce up to 2.7 million seeds in a year.

Root: Strong rhizomes.

Propagation: Tiny, lightweight seeds are readily spread by waterfowl and other animals. Vegetative reproduction by shoots and rhizomes.

Importance of plant: A European species introduced to North America in the early 1800s. It was distributed as an ornamental, but has become a serious pest plant. It is known as the "purple plague" because it displaces native wetland species. Provides minimal wildlife habitat. Has some medicinal uses in its native range.

Distribution: Native to Eurasia, but introduced nearly worldwide. Patches located throughout Washington and spreading to new locations.

Habitat: Marshes, lake shores, ponds, stream banks, ditches. Occasionally grows in upland areas.

May be confused with: Fireweed (Epilobium angustifolium) a perennial herb that inhabits dry, often disturbed sites such as clearcuts and roadsides. Fireweed flowers have 4 rounded petals. Also confused with hardhack (Spiraea douglasii) which is a native woody shrub rather than a perennial herb. Neither of these species have square stems. The related native plant hyssop loosestrife (Lythrum hyssopifolium) is smaller (to 40 cm) and has smaller, lighter-colored flowers.

Photographs: Lythrum salicaria, Lythrum salicaria closeup

Line Drawings: Lythrum salicaria