The role of seed cones in resolving the overall pattern of conifer phylogeny

ROTHWELL, GAR; STOCKEY, RUTH; ESCAPA, IGNACIO

Tokyo

Congreso; International Organization of Palaeobotany Conference; 2012

Chuo University

Systematic relationships among living conifers have become highly resolved through analysis of nucleotide sequences, plant structure, and rare genetic markers, but relationships among living species do not always accurately reflect the overall pattern of phylogeny for an ancient clade in which a great deal of extinction has occurred. Whole plant concepts for anatomically preserved conifer species from Paleozoic and Cenozoic strata have contributed to well-resolved phylogenies for species from each time span, but the almost total absence of whole plant reconstructions of anatomically preserved conifers from Triassic, Jurassic, and Lower Cretaceous sediments leaves relationships among the two groups in doubt. Up to the present, species that could link the two groups   have   been   considered   “transition   conifers”   of   uncertain   phylogenetic   relationships.   In   an   attempt to overcome this paucity of data we have hypothesized that anatomically preserved seed cones may be used as surrogates for whole plants to resolve the overall pattern of phylogeny for conifers. This approach relies heavily upon structural features of seed cones from a combination of fossil and living species. Through a program to describe more than 10 new species of Mesozoic conifer seed cones, and to reinterpret the structure of others, a data matrix of more than 40 species and 125 characters has been assembled and analyzed. Results of the phylogenetic analysis of this matrix resolve a conifer clade that is roughly concordant with results of analyses of living species only. Voltzialean conifers occur in a pectinate arrangement at the base of the tree, and more recent fossils plus crown group families form two clades. One clade includes several fossils and the Pinaceae while the other contains all of the non-pinoid living and extinct conifers. Placement of Cheirolepidiaceae within the tree is contingent on character scorings, and this emphasizes the importance of well-defined and explicit homology hypotheses for bract/scale complexes and other important seed cone structures.