Lythrum salicaria is a pretty perennial with a clumping habit.
The upright spreading stems have low mid green lance shaped leaves in opposite pairs along the stem.
During late spring to mid summer the stems are topped with long showy spikes of densely packed pinky mauve to purple flowers.
These are very attractive and great addition to garden borders, being well suited to informal and cottage style gardens.
They also go well in the increasingly popular wildflower meadows.
Note: In many parts of the USA it has been classified as a weed as it can be quite invasive.