Here's my current record for most ferns growing on top of each other!

A tree fern called a ponga (Alsophila tricolor) forms the base, growing on this tree ferns trunk is a hen and chicken fern (Asplenium bulbiferum).

Hen and chicken ferns grows little bulbils (baby ferns) on its fronds, when the bulbils are old enouph, they drop off to become a new hen and chicken fern.

These bulbils make up the final layer of ferns of my fern stack, making it a magnificent 3 layers of fern.