Dissertation Research: Molecular Phylogenetics and Interfamilial Relationships in the Portulacaceous Alliance of the Order Caryophyllales

9701125华莱士研究生温迪·阿普尔奎斯特在爱荷华州立大学罗伯特·华莱士博士的指导下，利用多年来在爱荷华州立大学积累的植物园资料和野外收集的资料，正在研究Basellaceae、仙人掌科、Didiereaceae和马齿苋科四个石竹科植物的系统发育或系谱关系。传统上用于这些植物分类的花和果实的形态特征，特别是大约500种马齿苋（马齿苋科），被怀疑在标记进化群体时是不可靠的，这可能是由于在干旱或沙漠生境中重复的趋同适应。来自叶绿体基因组DNA序列的新证据正在寻求提供大量可变但信息丰富的特征（突变或核苷酸替换），这些特征可用于测量这些植物之间的遗传差异。反过来，这些植物的一个可靠的系统发育框架将使研究它们的历史生物地理学和适应世界不同沙漠地区的模式成为可能。传统上，上面列出的四个石竹科植物在进化、生物地理学和适应性方面提出了有趣的问题，主要是在世界上的干旱或沙漠栖息地，主要是在南美洲、非洲和澳大利亚的南部大陆。如果没有可靠的种群系统发育（基于不受栖息地条件直接影响的遗传特征），就不可能将古代大陆漂移造成的模式与更近期的扩散和迁徙区分开来。本项目旨在通过现有的形态、染色体和解剖数据，从DNA序列信息中构建这些植物的系统发育框架。

9701125 Wallace Graduate student Wendy Applequist, under the guidance of Dr. Robert Wallace at Iowa State University, is studying the phylogenetic or genealogical relationships of plants in the four caryophyllalean families of Basellaceae, Cactaceae, Didiereaceae, and Portulacaceae, making use of botanical garden materials and field collections amassed over the years at Iowa State. The morphological features of flowers and fruits used traditionally in the classification of these plants, especially the c. 500 species of purslanes (Portulacaceae), are suspected to be unreliable in marking evolutionary groups, perhaps due to repeated, convergent adaptations in arid or desert habitats. New evidence from DNA sequences of the chloroplast genome is being sought to provide a large number of variable yet informative characters (mutations or nucleotide substitutions) that can be used to measure genetic divergences among these plants. In turn, a reliable phylogenetic framework for these plants will enable the study of their historical biogeography and patterns of adaptation to various desert regions of the world. The plants traditionally treated in the four caryophyllalean families listed above present interesting problems of evolution, biogeography, and adaptation, mostly in arid or desert habitats of the world, and primarily on the southern continents of South America, Africa, and Australia. Disentangling patterns caused by ancient continental drift from more recent dispersals and migrations has been impossible without a reliable phylogeny for the group, based on genetic features not directly affected by habitat conditions. This project is a focused effort to construct a phylogenetic framework for these plants from DNA sequence information, augmented by the morphological, chromosomal, and anatomical data in hand.