Lycopus europaeus (Gypsywort, Gipsywort, Bugleweed, European Bugleweed, Water Horehound, Ou Di Sun) is a perennial plant in the Lycopus genus, native to Europe and Asia, and naturalized in the United States.
It is reputed to have medicinal qualities and has been used by various peoples as an astringent, cosmetic, douche, narcotic and refrigerant. It has also been used to treat fever, hypothyreosis, sores and wounds. Several research studies have been undertaken on the properties of this plant.
The name Gypsywort comes from the belief that Gypsies were reputed to stain their skin with the juice of the plant, althgough Howard (1987) states that they used it to dye their linen.