Selaginella

"Like a green carpet," is one way to describe the pillowy mat of leaves of Selaginella.  It is an excellent terrarium plant or used in a pot mixed with other tropical plants.  The botanical and zoological gardens in Stuttgart, Germany have even created a large "lawn" of Selaginella in one of their greenhouses...impressive!  Selaginella thrives in high humidity and warm temperatures and would rather not dry out completely before watering again.