American mistletoe does photosynthesize its own food and gets only water and minerals from the host tree, but little carbon. Though this mistletoe may slow the growth of tree branches, it does not permanently damage its host. Mistletoe is more damaging to people because it contains a systemic poison, affects all parts of the body, and can be fatal. However, Native Americans as well as Europeans have used mistletoe for medicinal purposes. Though mistletoe berries are poisonous to people, they are relished by cedar waxwings, bluebirds and other songbirds.
Birds often wipe the seeds off their beaks onto other branches, helping to spread the plants.
Seeds are also dispersed by bird droppings, particularly waxwing droppings. The word mistletoe can be traced back to similar words in Old English, Norse and German, all meaning dung branch. The seeds of mistletoe berries are small and soft, lacking a seed coat. They are protected from a bird's digestive juices by a viscid, or sticky, layer containing chemicals that speed the seed through the digestive system. This same layer helps deposited seeds stick to limbs and twigs of host plants.