Abstract: Taking two characteristics of cyme width and size of glands in cyathium of Euphorbia pulcherrima as examples, this study aimed to select optimal example varieties used in the DUS test guideline of E. pulcherrima and provide scientific basis for subsequent revision of this test guideline. Two continuous years of measurements of cyme width and size of glands in cyathium of 75 varieties were collected and then the discrete distribution of these two characteristics of each variety was analyzed by using the box plot. According to the information of variability, distribution symmetry of measurements and outliers of cyme width and size of glands in cyathium of varieties manifested in the box plots, Fismars, Da Vinci and Olymp were selected as the example varieties for the three expression states（25.6~28.5 mm,31.6~34.5 mm and 37.6~40.5 mm） of cyme width. And Sonora Fire, Da Vinci and Peterstar were chosen as the example varieties for the three expression states（2.8~3.4 mm,4.2~4.8 mm and 5.6~6.2 mm） of size of glands in cyathium. The box plot is an efficient statistic method for the overall evaluation of quantitative characteristics of E. pulcherrima, which provides information including the expression range, median, tail length and outliers of measurements of cyme width and size of glands in cyathium of each variety. It can effectively analyze the uniformity and stability of quantitative characteristics, and is suitable for the selection of example variety in DUS testing, also provides a reference for selecting example varieties for other quantitative characteristics.

Key words: DUS test guideline of Euphorbia pulcherrima, quantitative characteristic, example variety, the box plot