This pretty little Begonia flowers almost constantly in the terrarium, and does perfectly fine in rather stagnant conditions.  For years mine has been growing in somewhat flooded loamy substrate without any issues.  It makes very nice ground cover and will form a mat over time.  It occurs in Cameroon, the Ivory Coast, and Equatorial Guinea. The leaves reach 1.5-2 inches and is an easy keeper, excellent ground cover.

The last photo is representative of the plants available. They are well rooted and shipped meticulously in their pots.