I suppose is a Lycopodium (or in any case some species in the same family).
It is a link between mosses and vascular plant. It is still vascular, without flowers but with spores. Not a fern, but defined "Fern ally" (like few other families which very few species, that nobody want to classify correctly).
Note: I could be wrong. Some mosses could be similar (but branches are too long), and also some flowering plant could have similar look, when they are small. On the other hand, I do no remember good-looking (so for pots) flowering plant.