桦木属（桦木科）大约有65个种和亚种，分布在亚热带到北极之间的不同生境中。桦木分类极其困难，部分原因是广泛的自然杂交与基因渐渗、多倍化以及形态性状的趋同进化。尽管研究者已利用少量 DNA 序列和分子标记来探讨桦木的系统发育，但该属的系统发育依然未得到较好的解决。这严重限制了桦木进化生物学以及生物地理学等一系列研究的开展。本项目拟对桦木开展 RAD-seq，以获得足够的数据来解决桦木属的系统发育、多倍体的起源以及国内桦木分类问题。申请人前期研究表明，在以白桦全基因组作为参考序列下， RAD-seq 非常成功的应用到桦木的系统发育研究中。这不但让我们对桦木物种进化及多倍体的起源有深入的了解，也为未来桦木育种工作奠定坚实的基础。因此，该项目具有重要的理论和应用价值。

Betula L. is a genus of Betulaceae with ~65 species and subspecies occupying various habitats from the subtropics to the arctic. The taxonomy of this genus is extremely difficult partly due to extensive hybridization and introgression, polyploidy and morphological convergence. Despite the fact that a few loci and molecular markers have been used to address the phylogeny of Betula species, it is still not resolved. This highly limited further research of this genus, such as evolutionary biology and phylogeography of Betula species. In this project, we will use Restriction-site Associated DNA Sequencing (RAD-seq) to build a resolved phylogeny of this genus and to infer the parental origins of the polyploid species. RAD markers have been successfully developed for a subset of Betula species in the preliminary studies and have proven highly useful in phylogeny with the whole genome sequence of B. platyphylla as the reference. The research will advance our understanding towards the species evolution of this genus and the origins of polyploid species. In addition, it will provide a framework of phylogeny within Betula, which is very important for tree breeding. Hence, the project is of great theoretical and practical significance.