Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants

Most of the 470-million-year history of plants on land belongs to bryophyte s, pteridophytes and gymnosperms, which eventually yielded to the ecologica l dominance by angiosperms 90 Myr ago(1-3). Our knowledge of angiosperm phy logeny, particularly the branching order of the earliest lineages, has rece ntly been increased by the concurrence of multigene sequence analyses(4-6). However, reconstructing relationships for all the main lineages of vascula r plants that diverged since the Devonian period has remained a challenge. Here we report phylogenetic analyses of combined data-from morphology and f rom four genes-for 35 representatives from all the main lineages of land pl ants. We show that there are three monophyletic groups of extant vascular p lants: (1) lycophytes, (2) seed plants and (3) a clade including equisetoph ytes (horsetails), psilotophytes (whisk ferns) and all eusporangiate and le ptosporangiate ferns. Our maximum-likelihood analysis shows unambiguously t hat horsetails and ferns together are the closest relatives to seed plants. This refutes the prevailing view that horsetails and ferns are transitiona l evolutionary grades between bryophytes and seed plants(7), and has import ant implications for our understanding of the development and evolution of plants(8).