First is a tiny bird called the Mistletoebird (Dicaeum hirundinaceum). The males even resemble a Christmas decoration.
Photo by David Kleinert
The Mistletoebird can be found anywhere mistletoe grows, which is almost everywhere. Most Australian mistletoes mimic the leaves of the tree which they parisitise, but once you get your eye in the distinctive drooping leaves and yellow or reddish colour (not to mention the distinctive red flowers) give it away upon a eucalypt or acacia. Anyway, the Mistletoebird feeds on the fruits of the mistletoe. These fruits are rather sticky and the mistletoebird's digestive system isn't very long - thus once the seed within the fruit comes out the other end of the bird, it's still covered with sticky fruit flesh. To dislodge this from their back ends the Mistletoebird's perform a rather amusing little dance upon a tree branch, where they drag their rear ends along a branch. Of course, the seed now sticks to a branch of a potential host tree. So the mistletoe and the mistletoebird remain dependant on one another.
Also in Australia, mainly in the south-west, there is a plant called Nuytsia floribunda which many locals refer to as the Christmas Tree because it flowers near Christmas.
Photo by O. Roberts
What many don't realise is that the Christmas Tree is also a mistletoe (adding to it's Christmasyness). It parisitises the roots of nearby trees, thus being able to form a tree like habit itself. This plant has been the bane of telecommunications and electricity companies in the past. Sometimes underground lines would go out for no discernable reason, but further research revealed these lines had been cut - by the Nuytsia! To the Nuytsia's parisitic roots an underground cable would feel just like a tree root, so the mistletoe had put out it's own strangling roots and inadvertantly cut the line.