Foliar Epidermal Micromorphology of Eleven Species and One Variety of Simple-Leaved Sorbus

To evaluate the taxonomic significance of leaf epidermal micromorphological characteristics, 11species and one variety of simple-leaved Sorbus from sect. Aria and sect. Micromeles native to China were investigated using light microscopy（LM）and scanning electron microscopy（SEM）. The results showed that the shapes of epidermal cells were irregular or polygonal-irregular. Anticlinal wall of polygonal cells was straight or arched, and anticlinal wall of irregular cells was arched or wavy. The area of epidermal cells varied significantly among taxa, and the size of the upper epidermal cells was larger than the lower epidermal cells. Cuticular ornaments such as ridges, striations, wrinkles, secondary thickening, thickened areas, and epicuticular waxy ornamented with crusts, granules, threads, and platelets were observed by scanning electron microscopy.Leaves were glabrous or with trichomes, and the position, color, density, and type of trichomes were important characters for the segregation of the taxa. Stomatal apparatuses were anomocytic and distributed in areole of abaxial epidermis. Guard cells had annular outer edges, with or without T-piece at stomatal pole. The cell size, length, width, area, density, and index of stomata varied significantly among taxa. Therefore, foliar epidermal micromorphology proved to be valuable for simple-leaved Sorbus taxa definition and identification.