Mistletoe

Mistletoe, Phoradendron spp.

Mistletoe are dioecious, parasitic plants within the order Santalales and can be found on almost all continents of the world. The berries of the female plant are small and white and a favorite of many species of birds. They have a sticky aspect to them that allows the seeds to remain attached to any branch on which they land. When the seed germinates, it grows through the bark of the tree. Rootlike structures called haustoria develop in the water-conducting tissue of the tree and gradually extend up and down the branch. An old, mature mistletoe may be several feet in diameter and cause large swollen areas to develop on the tree branch where it has affixed itself.

Another angle of the mistletoe infestation.

Many species of trees, from cottonwoods and oaks to maples and conifers, can be attacked by the broad range of mistletoe. A healthy tree can tolerate a few mistletoe branch infections, but a heavily infested tree can be killed. A tree may be saved by removing as many infected branches as possible. If allowed to grow for too long, though, the mistletoe may have established itself enough to return.

A more in-depth post on Mistletoe can be found on my Google+ post here written a month ago.