Morphological characterization of infloresence and trunk in golden-rain trees (Koelreuteria paniculata Laxm.)

Golden-rain tree (Koelreuteria paniculata Laxm.), growing in Korea and China, has a high ornamental value due to its yellow flowers that bloom in summer season. Moreover, its tolerance to air pollution, salt, and dry soil makes it has a lot of potential, both as a landscape tree and as a street tree in urban environments. This study was conducted to collect basic data on tree form and inflorescence characteristics of the golden-rain trees growing in six regions of Korea including Taean, Yeonggwang, Wando, Pohang, Andong and Jecheon. We investigated the length and width of inflorescences (LI and WI, respectively), the number of flowers per inflorescence (NFI), and the presence of bract and red color on petal bases. Additionally, tree form, clear-bole length, shape and straightness grade of the trunk were also examined. A total of 45 individuals were selected by the number of inflorescences, however, there was no significant difference in the size of inflorescences. NFI is higher in the coastal regions, for example, Yeonggwang, Wando, Taean and Pohang than in other regions. The individuals selected in Andong had the smallest LI, WI and NFI. Most individuals of all regions have bracts and red color in the petal base. Tree form accounted for 77.8% of irregular form and 22.2% of round form. In most areas, except Taean, main stems of trees were straight with a gentle curve, however, the individuals from Taean had wavy trunk and short clear bole length.