XVI International Botanical Congess

A phylogeny of Selaginellaceae was developed using rbcL gene sequences from 54 species. Two species grouped with the seed plant Ephedra tweediana, a highly incongruent result probably related to the exceptional levels of rbcL sequence divergence within Selaginellaceae. With this exception, results support monophyly of the family and a sister group relationship between subgenus Selaginella and a clade distinguished by rhizophore-bearing stems and comprising all other species. This group was partitioned into two subclades, each of which is characterised by a unique pattern of rhizophore development. Subgenus Tetragonostachys is monophyletic, whereas subgenera Stachygynandrum, Heterostachys, and Ericetorum are paraphyletic. The fossil record indicates that many clades originated in the Late Paleozoic and Early Mesozoic.