Phylogeny of Saxifragaceae and Relationships in Rosales Using rbcL Sequence Analysis

开花植物的进化或系谱关系往往在属的分类水平上很难理解。这些困难可能反映了在更高的分类学水平上，形态特征的趋同或并行进化更频繁地发生。虽然有许多这样的例子，但最有问题的是虎耳草科，包括醋栗、绣球和虎耳草。根据最初的定义，这个科由分布在世界各地的各种草本植物和木本植物组成，分为15-17个亚科。植物系统学家对这些不同类群的范围、分类等级(亚科、科)或它们之间的关系几乎没有一致意见。处理虎耳草科所涉及的分类学复杂性也需要对大目Rosales进行彻底的分析，它是该目的成员。近年来，DNA序列比较在确定更高分类水平的进化关系方面特别有帮助，这一点已经变得明显。华盛顿州立大学的道格拉斯·索尔蒂斯博士正在研究虎耳草科物种大样本之间的核苷酸序列差异，重点是与光合作用相关的基因rbcL。对rbcL序列数据的广泛分析将有助于澄清虎耳草科内部的关系，并与其他几个实验室产生的数据相结合，将有助于确定玫瑰双子叶植物之间的系统发育亲缘关系。由此产生的系统发育将提供一个进化框架，用于解释这些植物的形态和化学特征的变化，并提供它们历史上的生物地理信息。

Evolutionary or genealogical relationships in flowering plants are often poorly understood at taxonomic levels above the rank of genus. These difficulties presumably reflect the more frequent occurrence of convergent or parallel evolution in morphological characters at higher taxonomic levels. Although numerous examples of this exist, one of the most problematic is the Saxifragaceae family, including the gooseberries, hydrangeas, and saxifrages. As originally defined, this family consists of a diverse array of herbaceous and woody plants distributed throughout the world and placed into 15-17 subfamilies. Little agreement exists among plant systematists regarding the circumscription, taxonomic rank (subfamily, family), or relationships of these various groups. The taxonomic complexity involved in dealing with the Saxifragaceae also requires a thorough analysis of the large order Rosales, of which it is a member. It has become clear in recent years that DNA sequence comparisons can be particularly helpful in determining evolutionary relationships at higher taxonomic levels. Dr. Douglas Soltis of Washington State University is studying nucleotide sequence variation among a large sample of species of Saxifragaceae, focusing upon the photosynthesis-related gene rbcL. A broad analysis of rbcL sequence data will help clarify relationships within Saxifragaceae and in conjunction with data being generated in several other laboratories will contribute to determination of phylogenetic affinities among the rosalean dicots. The resulting phylogeny will then provide an evolutionary framework for interpreting change in morphological and chemical characteristics of these plants, and for informing their historical biogeography.