L. M.  Bowe, Coat, G., and dePamphilis, C. W., ?Phylogeny of the seed plants based on all three genomic compartments: extant gymnosperms are monophyletic and a close Gnetales-conifer relationship?, Proceedings of the National Academy of Sciences of the United States of America, vol. 97, pp. 4092-4097, 2000.