Some Asian Begonias have the unbearable likeness of being a fern - a case of parallel evolution perhaps. There are a few advantages I can think of. The water run-off will be more efficient and leaves will not rot as easily - a commonly encountered problem with jungle Begonias. Also, the broken leaf shape may deter a female butterfly, for example, from depositing eggs there, thinking it had already been already been visited by a compatriot.
Here are 3 species I can think of that would fit this bill :
Originally collected from an island of Polillo in the Phillippines a decade or so ago, Begonia polilloensis is characterised by its compound, bristly leaves that looked like a Selaginella and an inflorescence with many pink male flowers and a solitary female flower. It is surprisingly robust and cuttings are easy to strike. It can also withstand relatively drier apartment home culture conditions although it will definitely prefer a terrarium-like environment.
Begonia bipinnatifida has the very finely divided leaves that looks like filmy ferns. This native of Papua New Guinea has been known for almost a century but is not common in collections - I myself found it to be very challenging to grow. Like the previous species, this is another member of the bulky Petermannia Section which is a predominantly East Asian. I have seen very handsome shrubs in botanical institutions in the west (see below) .... .... but have yet so grasp the trick to make it grow well.
The third species is a novel un-named plant found on wet granite slopes in Southern Thailand. This plant really look like the Pteris fern and any casual observer would have dismissed it as such - unless it is caught flowering of course. I was told local Thais would eat this like a vegetable.
This species is recently named Begonia pteridiformis
Thai For. Bull. (Bot.) 38: 37–41. 2010.