Here's what it looks like now.

Most plants will quickly outgrow that jar. (Nothing wrong with that, just something for you to keep in mind. A planting in there will not likely be a long term piece.) Mosses may be your best option. Some interesting rocks or wood pieces could be used to create a little scene or landscape. Small figurines could also be utilized if you wish. Another plant you could use is Epipremnum 'Pincushion'. Plant only gets to be 3 or 4 inches tall and is a slow grower. Rarely see them for sale though. (On the plus side, works out for me as it makes it possible for me to sell off divisions of mine now and then. heh)

maidenhair ferns, heart fern, small adiantum, button ferns, brake ferns, & selaginalla Note: Concerns w/ collecting moss from outdoors Wild patches of moss can be very slow to recover from the depredations of collectors. Rather than damaging/destroying the micro-ecosystems these are a part of, it is best to leave them alone. Further more wild mosses are usually very specific with regards to their habitat. A moss growing on a rock is not going to be happy growing on wood mulch for example. Unless care is made to duplicate their microhabitat, they rarely flourish when brought indoors. Also wild mosses may harbor unwelcomed critters like snails.

"Totally" enclosed would be a death sentence for most plants -- especially in such a small terr. In providing sufficient light, the terr is likely to reach killing temps. Then there is the issue of mold ... stagnant air is perfect for such. (And almost without exception, orchids detest stagnant air -- even those which like high humidity.) IME, you'd be better off not doing a sealed terr. TM is spot on with regards to your having very limited options. Selaginella brownie and most true mosses are among the few plants that will stay really small. (Most other Selag could get too large without maintenance.) There are a number of micro-mini orchids, but your challenge there will be providing enough light without overheating the terr. There are also some Tillandsia species that stay quite mini, as well as Epipremnum Pincushion which maxes out at around 3-4 inches tall and is more of a clumper. Downside with that latter suggestion is that it isn't terribly easy to find. I sell off divisions of mine every so often to a gent who sells largely to folks in the pdf trade. He happily snaps them up whenever I offer them to him. Epipremnum Pincushion You could also look for Cryptanthus. There are some nice colorful ones. Some stay short but even those do have a spread of about 5-6" when mature.