Abstract
The phylogenetic relationships among the five groups of existing seed plants have been studied by generating a new molecular data set of mitochondrial small subunit rRNA sequences, and analyzing these data together with comparable data sets for the nuclear small subunit rRNA gene and the chloroplast rbcL gene. Combined analyses of all three genes strongly support monophyly of extant gymnosperms and the placement of Gnetales (although extremely divergent) within conifers as the sister group to the Pinaceae. Many morphological similarities between angiosperms and Gnetales (e.g. double fertilization and flower-like reproductive structures) arose independently. Proc. Natl. Acad. Sci. U. S. A. (2000) 97, 4086–4091.
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