These plants of Resurrection Fern (Polypodium polypodioides) generally grow in the trees or on rock walls this far south. They may have actually rooted in some of the stoney rubble which was very close to the surface.
The resurrection fern gets its name because it can survive long periods of drought by curling up and appearing dead. When just a little water is present, the fern will uncurl and reopen, appearing to resurrect.