Your best bet may be one of the Peperomia species. These vary from medium bushy types to lower sprawlers. But all like shade but need to be warm and humid!

Here is a link that might be useful: images peperomia

Depends too on just how small a terr is "small". You might be able do do some of the shorter growing ferns but I think the shortest is still about 5" tall if I remember correctly.

Thanks to both of you for sharing your thoughts. My terarium is only 12 inches round but it is my first expiriment and if I could find plants that work well I would gladly go to a bigger one. We don't have a lot of light because of surrounding trees but I so appreciate your suggestions and will look for both kinds of plants as I shop. I also have a bell jar I want to use successfully so your ideas would also fit there.

Thanks again !

Jean