Mistletoe

A branch of mistletoe with its characteristic sticky white
berries. Source

     Mistletoe is a shrub that grows on the branches of a tree or a larger shrub and gets water and many of its nutrients from its host tree or shrub. The fruit is white and sticky inside and it usually has a single seed. The word "Mistletoe" comes from the Anglo-Saxon words mistel, which means "dung", and tan, which means "twig". It is so named because the seeds often spread through the droppings of birds who eat the white berries. Mistletoe may cause a formation on its host known as the Witches' Broom, which can bear a resemblance to the mistletoe plant itself.
     In ancient times many cultures throughout Europe valued mistletoe as having mystical powers and properties. The ancient Celts believed that mistletoe could cure sleeplessness, high blood pressure, and tumors, as well as barrenness in animals. They also believed it to be an antidote to any poison. Mistletoe has significance in Greek and Norse mythology as well. It is also traditionally used as a Christmas decoration in some countries and in many of these countries tradition follows that a man and a woman standing under a hanging of mistletoe are obliged to kiss.
     In the Harry Potter series, mistletoe has magical properties, and Luna Lovegood claims that it is often infested with nargles.
     In the Pottermore, mistletoe is used as an ingredient for the Antidote to Common Poisons and the Forgetfulness Potion.