Letters to Nature

Nature 409, 618-622 (1 February 2001) | doi:10.1038/35054555; Received 25 July 2000; Accepted 27 November 2000

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

Kathleen M. Pryer1, Harald Schneider1, Alan R. Smith2, Raymond Cranfill2, Paul G. Wolf3, Jeffrey S. Hunt1 & Sedonia D. Sipes3

  1. Department of Botany, The Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, Illinois 60605, USA
  2. University Herbarium, University of California, 1001 Valley Life Sciences Building 2465, Berkeley, California 94720, USA
  3. Department of Biology, 5305 Old Main Hill, Utah State University, Logan, Utah 84322, USA

Correspondence to: Kathleen M. Pryer1 Correspondence and requests for materials should be addressed to K.M.P. (e-mail: Email: kpryer@fieldmuseum.org).

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.