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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 bryophytes, pteridophytes and gymnosperms, which eventually yielded to the ecological dominance by angiosperms 90 Myr ago1,2,3. Our knowledge of angiosperm phylogeny, particularly the branching order of the earliest lineages, has recently been increased by the concurrence of multigene sequence analyses4,5,6. However, reconstructing relationships for all the main lineages of vascular plants that diverged since the Devonian period has remained a challenge. Here we report phylogenetic analyses of combined data—from morphology and from four genes—for 35 representatives from all the main lineages of land plants. We show that there are three monophyletic groups of extant vascular plants: (1) lycophytes, (2) seed plants and (3) a clade including equisetophytes (horsetails), psilotophytes (whisk ferns) and all eusporangiate and leptosporangiate ferns. Our maximum-likelihood analysis shows unambiguously that horsetails and ferns together are the closest relatives to seed plants. This refutes the prevailing view that horsetails and ferns are transitional evolutionary grades between bryophytes and seed plants7, and has important implications for our understanding of the development and evolution of plants8.

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Figure 1: Phylogenetic relationships for all the main lineages of vascular plants inferred from maximum-likelihood (ML) analysis of the combined chloroplast rbcL, atpB, rps4 and nuclear small-subunit rDNA data set.
Figure 2: A portion of the chloroplast rps4 alignment.


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We thank R. Lupia, F. M. Lutzoni, B. D. Mishler, L. Newstrom-Lloyd and S. Zoller for critical comments on the manuscript; Z. Dabich, J. Bélisle, R. Lupia and D. Kieffer for assistance in rendering Fig. 1; F. M. Lutzoni and V. A. Funk for advice on phylogenetic analyses; I. Capesius, S. Boyles, B. Goffinet, M. Hasebe, M. Kato, M. Kessler, B. D. Mishler, R. Moran, J. Shaw, W. C. Taylor, Y.-L. Qiu, D. Wall, J. Wheeler, and greenhouse managers at Humboldt State University, University of California at Davis, University of California Botanical Garden at Berkeley, New York Botanical Garden for plant material; S. W. Graham, P. S. Soltis and J. Therrien for sharing unpublished sequence data; and D. Ferguson, E. Grismer, J. Irwin and L. Sappelsa for general assistance in the initial stages of the project. This work was supported by grants from the NSF to K.M.P., A.R.S., P.G.W. and R. C., the Green Plant Phylogeny Research Coordination Group (USDA grant), and by the Pritzker Foundation Fund of The Field Museum.

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Correspondence to Kathleen M. Pryer.

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Pryer, K., Schneider, H., Smith, A. et al. Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants. Nature 409, 618–622 (2001).

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