Objective  This paper aims to explore the degree of variation of phenotypic traits and main source of phenotypic diversity of Sophora japonica resources in Beijing urban area, comprehensively evaluate S. japonica and directly select the best germplasm, then provide theoretical support and breeding materials for the breeding of improved varieties of S. japonica.

  Method  In this study, 135 seedlings of S. japonica with DBH of 20 − 30 cm and tree age of about 23 years old were used as materials. According to their 26 phenotypic traits such as leaf position characteristics, fruit characteristics and crown width characteristics, the variation degree of phenotypic traits and the main sources of trait variation were analyzed by statistical methods such as analysis of variance, multiple comparison and principal component analysis, and the excellent S. japonica individuals were selected by quantitative evaluation and orientation.

  Result  The average coefficient of variation of the phenotypic traits of S. japonica was 25.08%, and the variation range of the coefficient of variation was 7.01% − 264.44%, among them, the variation coefficients of dorsal fluff, number of lenticels, leaf size and shape and leaf color were larger, and the variation coefficients of fruit size and thousand-grain mass were smaller. From the analysis of variance and multiple comparisons, it can be seen that, except for the basal leaf length to width, crown round rate, dorsal fluff, the other phenotypic traits of the S. japonica among populations reached significant or extremely significant levels, it showed that there were wide variations in phenotypic traits in different populations of S. japonicus, and the degree of variation was different. The results of principal component analysis showed that the first eight principal components represented 81.93% of the morphological diversity of S. japonica, among which, leaf size, leaf color, leaf shape and fruit fullness were the main factors causing differences in phenotypic traits among varied populations. Targeted screening of different types of ornamental traits of S. japonica by means of comprehensive evaluation of principal components, 10 excellent germplasms for each of 3 types of S. japonica were screened out, and the best germplasm came from 2 populations of Xingfu Street (XFDJ) and Aolin West Road (ALXL) in Chaoyang District of Beijing.

  Conclusion  The phenotypic traits of S. japonica germplasm resources in Beijing urban area are rich in phenotypic variation, and the degree of variation is high. Among them, the variation of leaf positions is the main source of phenotypic diversity, in addition, the variation degree of leaf and other vegetative organs of S. japonicus is greater than that of fruit reproductive organs, which provides abundant resources and great space for the selection and breeding of S. japonica varieties. In each of the three categories, 10 optimal germplasms were selected, which provide excellent propagation materials for the further collection, preservation and genetic improvement of the germplasm resources of S. japonica.