A Phylogenetic Study of Conifers Describes Their Evolutionary Relationships and Reveals Potential Explanations for Current Distribution Patterns
(1) Lexington High School, Lexington, Massachusetts
A phylogenetic tree is a diagram showing the evolutionary relationships between organisms. Gymnosperms produce cones to house their seeds and are commonly assumed to have originated during the Carboniferous era and conifers are a major division of gymnosperms. This study used the matK gene to construct a phylogenetic tree of conifer species (junipers, sequoias, Cupressacae, spruces, pines) with an outgroup of cycads. The matK gene was aligned using the program Seaview and the tree was created using PAUP. Analysis revealed that pines, spruces, sequoias, and Cupressacae have similar phenotypes while junipers and cycads appear to be distinct. The Bootstrap values of the tree show that the overarching clades are strongly supported and, therefore, are reliable. The purpose of this study was to generate hypotheses regarding the evolution of certain traits as well as the current distribution patterns of these species. Firstly, leaf type variability seems to have been determined by environmental selection during Pangea. Secondly, the winged seed phenotype dates back to the common ancestor of all conifers and is accompanied by a loss of winged seeds in the juniper clade. Finally, the distributions of junipers and pines have both been affected by other organisms including humans. The phylogenetic tree constructed in this study lends support to the hypothesis that North American pines originated from Asian pines. This phylogenetic study of conifers provides additional information regarding the evolutionary history of conifers. The hypotheses generated as a result of this study also provide additional ideas regarding the relative status of conifers in the history of evolution and new directions for future field research.