Have you ever been given a arrangement with willow twigs, and long after the arrangement passes on...and you have't got around to dumping out the twigs and cleaning the vase...you notice that the twigs are growing leaves? Well, it's most likely a willow. The stuff is uber hearty and the stuff reincarnation myths are based upon. The willow in the photo above is from such an arrangement.
Willow is a good root hormone as well, and one of the only truly organic methods out there. To make your own root hormone cut a few twigs, gently crush the ends and let them sit in water in the sun - similar to as if you were making "sun tea." The water can then be used as rooting hormone.
This tree is kept in a pot and aggressively pruned each year. I keep it specifically for rooting hormone.