Sneezewort (Achillea ptarmica) is a member of the yarrow family. The white flowers bloom in the summer.
According to a book Harry studied during his fifth year, sneezewort is "moste efficacious in the inflaming of the braine, and [is] therefore much used in Confusing and Befuddlement Draughts, where the wizard is desirous of producing hot-headedness and recklessness" (OP18).
Sneezewort is an ingredient in Confusing and Befuddlement Draughts (OP18).
According to Wikipedia, the "leaves can be eaten raw or cooked. Achillea ptarmica yields an essential oil that is used in herbal medicine. The leaves are used as an insect repellent."
From the Web
Achillea ptarmica from Wikipedia