Mistletoes are typically small, green-leafed shrubs, which commonly are semi -parasitic on trees. They are widely known for their decorative use during the Christmas season and because they can cause serious injury to certain trees. Mistletoes penetrate the bark of the host tree and attach to the conducting tissues by sucker-like organs that are generally considered to be modified roots. American mistletoes comprise about 200 species, mostly tropical, which are found from the Northern United States to central Argentina.