The leafy mistletoe that's associated with Christmas grows in hardwoods, such as oaks. Mistletoe is actually a parasitic plant. It attaches to trees and relies on them as a source of water and nutrients. Dwarf mistletoe is a destructive type of mistletoe that creates dense patches of deformed branches (known as "witches' brooms"). Mistletoe can be either female or male; only the female has the beautiful but highly toxic berries.