The skeleton-like remains of leaves are formed from xylem cells which contain high concentrations of lignin (the substance that makes wood woody) and persist after the more easily decomposed cells disappear. The pattern of branching follows Murray's law (as, by the way, do your circulatory and respiratory systems), a formula for relating the radii of daughter branches to the radii of the parent branch of a lumen-based system. Either that, or this is how the pixies make the leaves in the Azores, knocking up the basic structure before giving them to the trees to add the green stuff. One of these theories is more likely to withstand the rigours of scientific investigation than the other.
"Who are you?"
A giant woodlouse crosses a blasted landscape of iron rich sedimentary rock,... probably.