9306913 Swensen The Cucurbitaceae and Begoniaceae are two plant families whose members exhibit very distinctive morphological features, yet their phylogenetic relationships to each other and to related groups remain unclear. The cucurbit family is widely appreciated for its diversity of fruit structures (compare pumpkin, luffa, cucumber, chayote) whereas the begonias show a diversity of floral structures and leaf forms. Research by Drs. Swensen and Rieseberg is designed to use DNA gene sequences from the chloroplast and nuclear genomes for comparing members of these two families and several putative relatives. The new molecular data will be compared with traditional morphological characters used in the taxonomy of these plants, in order to determine areas of congruence and areas of disagreement. Where congruent, the data will allow recognition of reliable morphological features for taxon identification and for study of evolutionary change in characters. Disagreements will highlight problems of homology and possible differences in rates of molecular evolution. %%% Two related families, Datiscaceae and Coriariaceae, will also be studied. These include plants with symbiotic associations with nitrogen fixing actinorhizal bacteria. The research will investigate the evolution of this association and will provide hypotheses as to why it occurs in some groups and not in others. This information should prove useful in the induction of nitrogen fixing symbioses in agriculturally important plants.
