This lovely little fern is one of the easiest and fastest terrarium suitable ferns.  Its fronds only grow to about 1/2 inch, and it is tolerant of a wide range of conditions.  It does well mounted but will also grow terrestrially in sphagnum moss.  Given time, it will make a dense mat.  It is from the Caribbean.

Available plants are well rooted in 2″ pots.  They will be shipped potted.  The last photo is representative of the size plant you will receive.