Phylogenetic Relationships of the Ranunculidae and Basal Hamamelidae: Implications for the Early Evolution of Non-magnoliid Dicotyledons

点击翻译按钮获取中文摘要

9306533 Hoot The earliest lineages of flowering plants are known only as fragmentary fossils from Cretaceous strata, against which we can compare today's living descendants in order to reconstruct the likely course of evolution of angiosperms. With living plants, systematists analyze and compare morphological features of flowers, fruits, leaves, stems, and roots in order to build hypotheses about the likely direction of change, character by character, and then search for consistency in patterns of change across these and other sources of evidence (pollen, chromosome composition, secondary plant compounds). Modern methods of DNA analysis bring new data to bear on the problem, and Dr. Sara Hoot at the Field Museum of Natural History is analyzing three plant genes in groups of flowering plants hypothesized to be early angiosperms. Two of these are chloroplast genes and one is nuclear, thereby providing an internal control on patterns of phylogenetic divergence between the two plant cell genomes; sequences for the chloroplast atp B gene will be a novel and potentially powerful source of data. %%% New DNA sequence data will be obtained from numerous species of Ranunculidae and basal Hamamelidae, angiosperms thought to be among the earliest dicot lineages of the flowering plants. Patterns of phylogenetic divergence will be analyzed from the molecular data and compared with current views based on morphological features of extant and fossil plants. Areas of agreement between the two sources of evidence will allow study of the evolution of floral form in early angiosperms; areas of disagreement will highlight weaknesses in our understanding of rates of gene evolution or of homology of anatomical characters.