占三分之一被子植物多样性的蔷薇类由COM分支、固氮分支和锦葵类组成。基于叶绿体基因和线粒体基因所重建的COM分支在蔷薇类中的系统位置相互矛盾，这是被子植物中争议最大，也是备受关注的高级分类阶元的系统发育难题。本项目拟利用高于以前研究的类群取样密度（约200个分类群），选取来自三个基因组的17个基因，通过多种基因进化特性分析，剔除所选基因中可能的系统发育噪音，建立能反映各自进化历史的基因树，并相互比较其拓扑结构，从而确定不同基因组的基因所建立的COM分支的系统位置是否真的存在冲突；同时，通过随机删去5%-90%的类群并反复进行系统发育分析，探讨类群取样密度对COM分支系统位置的影响。简言之，本项目将从基因的进化特性、进化历史和类群取样密度等方面探讨COM分支在蔷薇类中的系统位置。本项目的实施不仅能更深入地理解蔷薇类的系统发育，还可为其他类群在解决相似问题时提供参考。

Tremendous progress has been made in understanding the relationships of angiosperms during the past two decades. Molecular classification system of angiosperms has been established at order and familial level. Systematic position of COM clade within rosids, however, remains uncertain, because previous analyses from chloroplast (cp) or mitochondrial (mt) genes have produced conflicting topologies. This is the most controversially phylogenetic problem within angiosperms at higher taxonomic level. In this project, we will use 17 molecular loci from three genomes (cp 7, mt 4, and nulear 6) with a more extensive sampling than in any previous studies(ca. 200 taxa). By evolutionary staturation, RY coding, slow-fast site analytical, and RNA editing methods, phylogenetic noises will be examined and be deleted from subsequent analysis. Meanwhile, the influence of taxon sampling dentity will also be investigated by random deleting 5%-90% terminals. That is, we hope to clarify the systematic position of COM clade within rosids by analyzing evolutinary characteristics and evolutionary history of every genes selected and by examing the effect of taxon sampling on phylogenetic analyses. This research will improve our understanding to the relationships of angiosperms.