Before there were forests, wispy plants fell on each other in their struggle to reach the sun, like clumsy teenagers unsure of their growing bodies. Then one plant evolved a simple woody stem. It could grow taller than the other plants, and it stole light from them. It poisoned them with shade. Wars ensued that have lasted hundreds of millions of years. Trees of many kinds arose and struggled with each other to be taller. Any species that does not participate in battle loses out in the darkness of the understory—any species except a few. Those in the clan of the sandalwood evolved a way out of the darkness. They survived by stealing from the trees what they had spent their tall stems fighting for.
Sandalwood discovered deceit. Its roots kissed the roots of trees and slipped inside them to steal. But sandalwood still needed to grow up a little and put out a few green leaves to have enough sugar to thrive. And then came mistletoes. Mistletoe is a common name for several independent lineages descended from sandalwood. Like their ancestors, mistletoe species sink their roots into trees. Unlike those ancestors, they do so in the sky.
The story continues to explain how mistletoe developed its way of reproducing in the treetops. Link
(Image credit: Flickr user Darwin Bell)