Yarrow is a wild flower once common across much of Europe, also known as Milfoil, and it is an important medicinal herb. It is most commonly used and associated with stopping bleeding and it is a styptic (aids in blood clotting) and an astringent (makes tissue contract). It’s also antiseptic and so this plant is linked with poultices for wounds.
It is side to have been used to stop the wounds of Achilles (hence it’s Latin name).
An infusion of the fresh or dried leaves is used to help head colds or influenza as it encourages sweating and reduces fever. A cooled infusion can also be used to wash wounds.