Extant vascular plants comprise free-sporing "pteridophytes" (lycopods, Psilotaceae, Equisetum, and ferns) and seed plants (gymnosperms and angiosperms). The evolution of vascular plants is mostly a 470-million-year history of pteridophytes and gymnosperms, which ultimately led to the domination of our terrestrial ecosystems by angiosperms 100 million years ago. Pteridophytes traditionally are depicted as having various paraphyletic relationships to seed plants and are often thought of as "intermediate evolutionary grades" of relatively minor significance in early land plant evolution. Phylogenetic estimates based on single genes and/or morphology yield weak evidence for the divergence and relationships among these major groups of vascular plants. This is not entirely surprising given that, with the exception of angiosperms, they all evolved in the Paleozoic and had diverged by the late Devonian (ca. 400 mya). The long independent history of each of these lineages ensures that resolving their relationships is not likely to be revealed by a single data set. Data from four genes (rbcL, atpB, rps4, nrSSU) and morphology was tested for congruence and results from the combined analysis strongly corroborate several weak inferences made from single data set trees. However, the clear resolution provided by the combined analysis for a basal dichotomy between seed plants and all other (non-lycophyte) "pteridophyte" lineages is novel. This result differs remarkably from most topologies found in the separate analyses for each of the five data sets. Robust support for Psilotaceae + Ophioglossaceae, as well as relationships among basal fern groups will also be discussed.

Key words: congruence and combined analysis, genes, morphology, phylogeny, pteridophytes, seed plants