Actually, there are a handful of plants that can propagate from leaf cuttings! [Fun fact he learned during all the plant research he's been doing over the past month. Hey, it came in handy after all!] I have no idea if the World Tree can, though.

Likewise, I have no idea if it could be used in some kind of spell, as far as magic goes. My Herbalism ability only helps me figure out uses plants might have for the purpose of potions or salves. Chemists aren't spellcasters, so...