Mistletoe is the mysterious plant you look up to see and wonder why it chooses to grow there.

How did it get there?

How does it survive?

What is its role in nature?

American mistletoe is the country's only shrub that is parasitic on the branches of broad-leaved trees, according to Helen Hamilton, president of the John Clayton Chapter, Virginia Native Plant Society (www.claytonvnps.org).

The plant's thick, green leathery leaves are evergreen and wedge- to egg-shaped and one to two inches long. Tiny yellow flowers bloom on the smooth, jointed stems in late fall, followed by round, white berries -- only the female plant produces the fruits.

Mistletoe, botanically called Phoradendron serotinum (leucarpum) takes water and nutrients from the plant it grows on, but it also produces some chlorophyll and draws energy from the sun, says Hamilton.

Having no roots of their own, they produce structures called "sinkers" and "haustoria" that penetrate the host's tissue.

Found in almost every county in Virginia, American mistletoe thrives in trees from New Jersey to southern Ohio, southern Indiana and southern Missouri and south to Florida and Texas. Usually favoring a few species in any given area, it seems to especially like hickories and oaks.

During this time of year, mistletoe takes on a romantic role, hanging around the house and giving couples a place to kiss. The custom is said to have originated in Scandinavia, where it was considered a place of peace -- enemies and couples would make up under it.

In medicine, European mistletoe has been used as an antidote to poison and to treat seizures and headaches. It's currently being investigated as an anticancer treatment, says Hamilton. However, all parts are poisonous to cats and dogs and some humans, causing gastrointestinal upsets, even death.

Mistletoe seeds are distributed by birds in three ways: eaten and passed in droppings, swallowed and regurgitated or stuck in a bird's beak and rubbed into a tree crevice when a bird cleans its beak on bark.

A sticky substance poisonous to man covers the seeds but birds relish it all. The plant provides important food and nesting sites for many birds, including bluebirds and cedar waxwings.

Contrary to popular belief, some mistletoe on a tree will not kill its host plant. It would take dozens of plants on separate branches and even then the decline would take years.