Selaginellaceae are a cosmopolitan family of heterosporous lycopods that originated during the Paleozoic Era. We present a phylogeny of the group based on rbcL gene sequences from a representative sample of living species, currently standing at approximately 10% (63 taxa). Monophyly of some widely recognised groups is upheld (Selaginella, Tetragonostachys, and Articulatae), but others are shown to be paraphyletic (Stachygynandrum, Heterostachys, and Ericetorum). We present an evaluation of some of the morphological data used in previous classifications. Leaf dimorphism correlates poorly with the major divisions in the family. However, some of the new groups recognised on molecular criteria are shown also to have distinctive morphological characteristics (e.g., patterns of rhizophore development, megaspore wall ultrastructure). Megaspore wall ultrastructure is singled out as one characteristic that might be of exceptional utility in calibrating the phylogenetic tree. Our results have implications for the interpretation of xerophytic strategies within the family. "Resurrection plants" appear to have evolved at least three times.

Key words: lycopods, phylogeny, rbcL, resurrection plants, Selaginellaceae