Begonia pteridiformis was discovered in 2009 and has only been available in cultivation for a few years.  Native to Peninsular Thailand, it is found on wet limestone regions of lowland evergreen forest.   It is named for the unique arrangement of leaves that resemble a fern (Pteridi) at quick glance.  Growing to only about 10″ tall, it makes an excellent Begonia for the terrarium, although I have also seen it grown in open air successfully.  A tuberous species, which like many tuberous species, does not like it too wet, and should be allowed to dry out between waterings.  Despite it’s thin leaves, they are actually quite durable and can be used to propagate with a high success rate.  It might be best to turn the leaves upsidedown on a barely moist substate for germination, as the leaves rot easily if kept too wet.  During dormancy, cease watering for a season and keep in lower light, and it will come back eventually.

Patrick Blanc has some incredible images of a green type growing on limestone, not to be missed!

Even large cuttings taken and repotted can bloom in a short period of time, as here, plants taken off a larger plant are blooming one month later.

The segmentation of the stem below is reminisce of bamboo corms.

The plant growing below petered out quickly, as the clay medium I think was too moisture-rich.  It looked nice for a few months.

The original paper of discovery can be found here, with some excellent photos.