Mistletoe is a plant with smooth oval leaves and small white berries that grows as a parasite on tree branches, sending roots into the tree to take water and nutrients. You might spot clumps of mistletoe high in oak or apple trees, where it forms round bunches of greenery even in winter when other leaves have fallen.

Interestingly, mistletoe berries are poisonous to people but provide winter food for birds, which then spread the seeds to new trees. Despite its unglamorous name, the plant's ability to stay green through winter made it seem special to ancient cultures, helping explain why it became part of holiday celebrations.