Abstract: Physiological age (PA), proposed by botanists, is used to describe the growth process of plants. Rational division of PA plays an important role in the analysis of the growth rhythm of plants and the establishment of tree growth models. However, it is difficult to classify the PA for tall perennial plants with a complex topological structure and, until the present, no systematic methods have been developed. In order to classify the PA of plant organs quickly and suitably, we propose a new automatic method for dividing the PA of plants, based on actual measurement data of Populus×euramericana cv. ‘Neva’. Our experimental results show that the proposed method, which can surmount the problems of artificial methods, i.e. strong subjectivity and operational complexity, is feasible for the determination of PA in perennial trees.