Introduction and overview of conifer phylogeny

ROTHWELL, GAR; CAMPBELL, C; ESCAPA, IGNACIO; GERNANDT, D; HOLMAN, G; KELCH, D; LITTLE, D; MAPS, G; MATHEWS, S; STOCKEY, RUTH

Melbourne

Congreso; XVIII International Botanical Congress; 2011

Phylogenetic studies of conifers have achieved progressively finer resolution of relationships through multiple approaches that utilize a combination of traditional and highly sophisticated modern techniques. An ever increasing body of nucleotide sequence data has provided the basis for resolving relationships among living plants to the species level. The coding of nearly 400 morphological characters for exemplar species of living and extinct species provides an additional new tool for the study of relationships. When a combination of living and extinct conifers is studied, analyses of morphological characters yield resolution of relationships among stem and crown group conifer families, provide calibrations for inferring the ages of living conifer families and genera, and serve as tests for hypotheses of relationships derived from the analysis of nucleotide sequences and rare genetic markers. Although some subsets of the data suggest that different groups of conifers may have undergone parallel evolution from a Paleozoic grade of coniferophytes, or that gnetophytes may be variously nested among the conifers, a preponderance of evidence from nucleotide sequences, morphological characters, and rare genetic markers supports the hypothesis that conifers form a monophyletic group. Phylogenetic analyses of both nucleotide sequences and morphological characters resolve Pinaceae as the sister to all other families of living conifers. Those analyses also resolve Podocarpaceae + Araucariaceae as the sister group to Sciadopitydaceae + (Cupressaceae + the taxads). Both phylogenetic analyses and transformational series of seed cone morphologies reveal changes leading from Pennsylvanian age walchian V oltziales, through Permian age voltziacean Voltzales, to either Pinaceae, or to Sciadopitydaceae and Cupressaceae, and resolve tree topologies that generally agree with those from the analysis of living species. These combined approaches strongly suggest that all families of modern conifers have seed cones that are derived from a compound shoot system, and reveal that the extinct Cheirolepidiaceae subtends crown group Pinaceae on the tree. Together these combined approaches yield a much more highly resolved phylogeny for conifers than previously has been possible, and new analytical methodologies both increase our understanding of homoplasy within the data set and help strengthen our confidence in the accuracy tree topology.