What kind of disease is it?

Parasitic Fungi.

What are the host plants?

Oak and Apple trees.

How does it grow?

Bird poop out seeds, grows on a wide range of trees.

Why do we kiss under it?

This god Baldur, who was loved by everyone. and they found protection in him. "took an oath from fire and water, iron and all metals, stones and earth, from trees, sicknesses and poisons, and from all four-footed beasts, birds and creeping things, that they would not hurt Baldur." He was made invincible. Stones, Arrows, and other things were thrown at him to see if he was really invincible, and nothing hurt him. When his mother asked for him to be invincible she forgot the put in mistletoe, so this guy Loki made a dart out of mistletoe and killed him in front of everyone. His mother was so devastated that she told everyone that mistletoe would not be used as a weapon, but that anyone who go under it will be kissed. (http://mentalfloss.com/article/31977/why-do-we-kiss-under-mistletoe)

3 facts.

  1. More than 20 species are endangered.
  2. There are 1,300 species know worldwide.
  3. Toxic to people, but the berries have high protein for animals.