Bilipatra

Shiv Puja.  It is done with bilipatea

This is what it looks like.  Traditional 

However if you read bilvastaka it says the base is Brahma, proximal is shiv and middle is Vishnu!

This is a great clue that the bilipatra is not a leaf but something else.  

A very advanced yogi knows what it is and how to pray to shiv with it.  It is not the leaf