A phylogenetic framework is developed for the clubmoss family Selaginellaceae based on maximum parsimony analyses of molecular data. The chloroplast gene rbcL was sequenced for 62 species, which represent nearly 10% of living species diversity in the family. Taxa were chosen to reflect morphological, geographical, and ecological diversity. The analyses provide support for monophyly of subgenera Selaginella and Tetragonostachys. Stachygynandrum and Heterostachys are polyphyletic. Monophyly of Ericetorum is uncertain. Results also indicate a large number of new groupings not previously recognized on morphological grounds. Some of these new groups seem to have corresponding morphological synapomorphies, such as the presence of rhizophores (distinctive root-like structures), aspects of rhizophore development, and leaf and stem morphology. Others share distinctive ecological traits (e.g., xerophytism). For many groups, however, no morphological, ecological, or physiological markers are known. This could reflect patchy sampling and a lack of detailed knowledge about many species. Despite a lengthy fossil record dating from the Carboniferous Period, cladogram topology indicates that most of the living tropical species are probably the products of more recent diversifications. Resurrection plants, extreme xerophytes characterized by aridity-driven inrolling of branches and rapid revival on rehydration, have evolved at least three times in quite different clades.