【Objective】Genome sizes and micromorphological characteristics of leaf epidermis in five species representing Sorbus Sect. Alnifoliae together with two taxonomically controversial varieties were studied. The purpose of this study was to explore the taxonomic significance and the correlation between genome size and cell size. 【Method】The genome size was estimated by flow cytometry. Qualitative and quantitative traits of leaf epidermis were studied by optical and scanning electron microscopy【Result】The flow cytometric genome size estimation revealed that seven investigated taxa possessed very small genomes. The nuclear DNA content varied from 1.348 pg in S. yuana to 1.586 pg in S. zahlbruckneri. Though all are diploids, significant variation of genome size was observed among taxa. Polygonal-irregular or irregular epidermal cell shape, straight, arched or undulate of anticlinal walls, were determined using light microscopy. Patterns of cuticular ornamentation such as smooth, thickened areas, ridges, reticulate and folds and epicuticular wax types such as crusts, granules, threads and platelets were observed by scanning electron microscopy. Simple single ribbon-like trichomes are located on the lower epidermis of four taxa. Stomatal apparatuses are anomocytic and confined to areole on abaxial, not adaxial, epidermis. Guard cells with or without obvious annular outer edges. Significant variations in epidermal cell area, stomatal width, area, density and stomatal index, were observed among the taxa. There was a positive relationship between genome size and stomatal length, width, area and epidermal cell area and a negative relationship with stomatal density and stomatal index. 【Conclusion】Genome sizes, qualitative and quantitative traits of leaf epidermis allow clear delimitation and identification of the seven taxa. The treatments of S. alnifolia var. angulata and S. alnifolia var. lobulata as synonyms of S. japonica are not supported and the latter two names are suggested to be reinstated here.