東海大學 生命科學系

The present review summarizes and discusses advances in the past 15 years on the molecular phylogeny and evolutionary biology of the extant four gymnosperm groups (Cycadophyta, Gnetophyta, Ginkgophyta, and Coniferophyta). Discrepancies between traditional and molecular-based phylogenies are critically discussed. Monophyly of the four extant gymnosperm divisions appear to be consistently supported by increasing evidence from analyses of various gene sequences and comparative chloroplast genomics. A recent discovery of fossilized Gnetalean cones from Permian (ca. 270 MYA) provides unequivocal evidence that the gnetophytes have coexisted with the conifers since the Paleozoic. Therefore, a sisterhood relationship of gnetophytes and conifers seems reasonable. However, more studies are required to justify the ‘gnetifer’ (gnetophytes and conifers are sister groups) and ‘gne-pine’ (gnetophytes and Pinaceae are sister groups) hypotheses. The taxonomic standings of both Taxales and Taxodiaceae have been refuted by molecular data. Future directions of research should address molecular mechanisms that regulate the development of reproductive organs in the four gymnosperm groups, in addition to various homoplastic characteristics that found in gnetophytes and angiosperms. In the past five years, the explosive accumulations of sequence data from chloroplast and mitochondria genomes have resolved several key questions in the angiosperm phylogeny. In this regard, matched effort should be made for representative gymnosperms in order to improve understanding of seed plant phylogeny as a whole.