Baneberry (Actaea spp.) is a genus of flowering plants.
The berries are the most poisonous part of the plant, and they are presumably used in the making of the Baneberry Potion.
Behind the scenes
The picture of the Baneberry Potion depicts a Baneberry as a small branch with green leaves and clusters of both red and white berries. This is odd - varieties of Actaea may have red, black, or white berries, but two colours together is unusual.
Baneberry, also known in England as Herb Christopher, was once believed to ward off plague, insects, and vermin but attract toads.