Decodon
Decodon verticillatus
Decodon verticillatus (L.) Ell.
Engl.: swamp loosestrife, grass-poley, swamp willow-herb.
Bot. syn.: Anonymus aquatica Wright, Lythrum verticillatum L., Nesaea verticillata Kunth.
A herbal distance course
Henriette's herbal is one of the oldest and largest herbal medicine sites on the net. It's been online since 1995, and is run by Henriette Kress, a herbalist in Helsinki, Finland.