Chloroplast DNA Phylogeny for the Cyatheaceae

热带蕨类植物是现存唯一保留了早期陆地植物特征的原始繁殖方式（通过孢子而不是种子）的树木。Cyathea复合体的树蕨不同于其他蕨类植物，它们缺乏多倍体（多套染色体），并产生可育的二倍体杂交种。Drs。Diana Stein和David Conant将构建一个树蕨的系统发育或进化关系方案，作为分析这一类群的物种形成机制的框架，并解决迄今为止命名的种和属的分类冲突。其他科学家试图用趋同或平行进化的形态学特征（如叶鳞特征）来构建这一群体的系统发育。Drs。Stein和Conant将研究树蕨叶绿体DNA突变差异的变化，以确定分类群之间变化的模式和方向。叶绿体突变差异更直接地反映了物种之间的遗传差异，并为追踪这些植物的进化变化过程提供了很大的希望。

Tropical tree-ferns are the only trees alive today that have retained the primitive type of reproduction (by spores rather than by seeds) characteristic of the earliest land plants. Tree ferns of the Cyathea complex of species differ from other ferns in their lack of polyploidy (multiple sets of chromosomes) and by the production of fertile, diploid hybrids. Drs. Diana Stein and David Conant will construct a phylogeny or scheme of evolutionary relationship for the tree-ferns to serve as a framework for analyzing speciation mechanisms in this group and to resolve conflicting taxonomies of the species and genera named thus far. Attempts by other scientists to construct phylogenies for the group have used morphological features (such as leaf scale characters) subject to convergent or parallel evolution. Drs. Stein and Conant will examine variation in mutational differences in the chloroplast DNA of tree-ferns, to determine the pattern and direction of change among taxa. Chloroplast mutational differences provide a more direct reflection of genetic divergence among species, and hold great promise for tracking the course of evolutionary change in these plants.