Abstract: The complexity and heterogeneity of roots are important characteristics that hinder root research. Various root classification methods have been developed to classify roots into relatively homogeneous subcategories for specific scientific questions and root traits. Each classification method aims to subdivide different root subcategories from different perspectives using different rules. When conducting root research, it is crucial to select an appropriate method based on research objectives and the homogeneity of obtained root subcategories. As each root classification method has its advantages and disadvantages and can provide useful information about root function, multiple root classification methods coexist. To choose a suitable root classification method, a comprehensive understanding of the advantages and relevance of different methods is necessary. However, there is a lack of comprehensive literature reports that compare root classification methods, which hinders root researchers from selecting appropriate methods. We addressed this gap by summarizing and comparing five classification methods of fine roots. We review the progress and direction for the application of fine root classification to facilitate root researchers in selecting appropriate classification methods when studying fine root physiological and ecological functions.

Key words: absorptive root, diameter class, growth axis order, segment order, transport root