柳属植物雌雄异株、通常先花后叶，很难在同一时间观察到同一种的雌花、雄花和成熟叶片的完整形态，加之种间存在广泛的自然杂交，分类研究极为困难。分子证据显示该属为一单系，属内分两支，一支为柳亚属，另一支主要由皱纹柳亚属和黄花柳亚属构成，但各分支内系统发育关系尚不明确，尤其是皱纹柳亚属和黄花柳亚属构成的次级分支。这一分支内的亚属和组完全基于宏观形态划分，亚属间界限模糊，组间界限也不清晰，是分类学研究中急需解决的问题。因此本课题在大量前期研究基础上，选用中国皱纹柳亚属和黄花柳亚属31组65种、欧洲的2组2种和外类群3种，利用限制性酶切位点关联DNA测序（RAD-seq）技术进行系统发育研究；并联合形态特征进行性状演化分析，对用于亚属和组划分的主要形态性状的系统学和分类学价值进行评价。通过本项目的研究，揭示中国皱纹柳亚属和黄花柳亚属内部系统发育关系，为中国柳属的全面修订提供科学依据证据。

Salix is a taxonomically difficult genus, due to dioecious and different time of development for flowers and leaves which prevents the observer from seeing all relevant characters on a single plant, and comparatively high frequency of natural interspecific hybrids. The genus has two major clades, subgenus Salix clade and Vetrix-Chamaetia clade. The relationships under two clades remained unresolved, especially the Vetrix-Chamaetia clade. The subgenera and sections of this clade are based on morphological characters, their boundaries are unclear. To elucidate the internal relationship of Vetrix-Chamaetia clade and evaluate present sectional classification, we will employ RAD-seq (restriction-site-associated DNA sequencing) conduct phylogenetic analysis covering 31 Chinese sections 65 species and 2 European sections 2 species of Vetrix-Chamaetia clade and 3 species as outgroup based on our previous work. Then we will reconstruct the evolutionary history of each chosen character according to the phylogeny. This study will provide more convincing bioinformatics evidence to understanding the Vetrix-Chamaetia clade. The work also will lay a foundation for the taxonomic revision of Salix in China.