Selaginella is a large genus of over 700 species. According to Page & Bennell (1986) eight species are cultivated in Europe, usually for groundcover in greenhouses. Out of these, Selaginella kraussiana is by far the commonest although its cultivation might have decreased in recent times.
A second species, Selaginella helvetica (L.) Spring, is an extinct native species, formerly known from damp, siliceous rocks between Eupen and Malmédy (Hautes Ardennes). It is a much more slender species with stems up to 10 cm long, not articulating at branches (vs. 25-100 cm long, articulating at branches in Selaginella kraussiana).
Literature
Lawalrée A (1964) Selaginella. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1. Cambridge University Press, Cambridge: 4-5.
Page C.N. & Bennell F.M. (1986) Selaginella. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 1: 3-5. Cambridge University Press, Cambridge.
Zhou X.-M., Rothfels C. J., Zhang L., He Z.-R., Le Péchon T., He H., Lu N. T., Knapp R., Lorence D., He X.-J., Gao X.-F. & Zhang L.-B. (2016) A large-scale phylogeny of the lycophyte genus Selaginella (Selaginellaceae: Lycopodiopsida) based on plastid and nuclear loci. Cladistics 32: 360-389. [available online at: https://www.researchgate.net/publication/281275639_A_large-scale_phyloge...
Zhou X.-M. & Zhang L.-B. (2015) A classification of Selaginella (Selaginellaceae) based on molecular (chloroplast and nuclear), macromorphological, and spore features. Taxon 64(6): 1117-1140. [available online at: https://www.researchgate.net/publication/288887777_A_classification_of_S...