With more than 700 species, Selaginella is the largest group of heterosporous lycopsids. Recent and ongoing molecular studies have provided new hypotheses for the phylogeny and circumscription of subgeneric groups and demonstrated strong support for a monophyletic Selaginella subg. Tetragonostachys. Including ca. 50 species, members of this subgenus are nearly cosmopolitan in distribution and are usually characterized by their possession of isophyllous microphylls and tetrastichous sporophylls. Although the subgenus itself is clearly defined, relationships among its component species have been debated. To evaluate existing classification schemes and provide a comparative basis for continuing molecular analyses, a phylogenetic analysis based on morphological features is underway. This analysis supports the monophyly of "Tetragonostachys" and, although surveys across all taxa are not yet complete, preliminary synapomorphies include the origin of rhizophores from the upperside of the stem, stomates restricted to an abaxial fold of the microphylls, and the presence of vessels. Within "Tetragonostachys," two monophyletic groups, corresponding to Tryon's series "Eremophilae" and "Arenicolae," are strongly supported. The "Eremophilae," largely restricted to the southwest US and Mexico, are defined by a prostrate growth habit and slight dimorphy between upper and lower microphylls. The "Arenicolae" group, having an erect habit, uniform leaves, and continued growth by rhizomes or stolons, exhibits a disjunct distribution between northern Africa and North America, paralleling that observed in several angiosperm taxa. Tryon's "Sartorii" and "Rupestres" groups appear polyphyletic. Within "Sartorii", however, there is support for a monophyletic group restricted to southern Africa, Madagascar, and India. Explicit phylogenetic analysis of comparative morphological data appear to provide clues for testing vicariance versus dispersal hypotheses implicated in the distribution and speciation of Selaginella.

Key words: Dispersal, Lycopsids, Morphological analysis, Selaginella, Vicariance