Lythrum salicaria is an herbaceous perennial plant, which can grow 1-1.5 m tall, forming clonally colonies 1.5 m or more in width with numerous erect stems growing from a single woody root mass.
The stems are reddish-purple or red to purple and square in cross-section. The flowers are reddish purple. Flowering lasts throughout the summer. Bright crimson leaves at the onset of autumn.
The flowers are pollinated by long-tongued insects, including bees and butterflies. A number of insects use Lythrum salicaria as a food resource.