Leaf Epidermal Micromorphology Of Sorbus Section Sorbus And Its Taxonomic Significance

The genus Sorbus L.(Rosaceae,Maloideae)contains Sect.Sorbus,Sect.Aria and Sect.Micromeles,in which the sect.Sorbus and the sect.There are a lot of hybrid and apomixis polyploids in the Sect.Sorbus,which is the difficulty of classification.Leaf Epidermal Micromorphology of 44 species and 9 varities were obeserved,and taxonomic value traits and phylogenetic relationship were analyzed in this research.Accordingly,an identification key to species of Sect.Sorbus was compiled.The main conclusions are indicated as follows.1 Shape and size of leaf epidermis cellsIn the Sorbus Sect.Sorbus,the shape of leaf epidermis cells is mainly polygonal,and only the adaxial epidermis cells of S.filipes,S.poteriifolia,S.reducta and S.reducta var.pubescens are irregular.There is only one type of anticlinal walls pattern of polygonal cells,which is straight-arched,and there are three types of anticlinal walls patterns of irregular cells:sinuolate,sinuous and sinuate.For the periclinal walls of plant cells in Sect.Sorbus,most of the plant cells are sunken,a few of them are protuberant,and some of them can not be observed directly.The size of leaf epidermis cells varied greatly in different taxa.The area of adaxial epidermis cells ranged from 355.19?m2 to 1685.76?m2,among which the smaller was S.rehderiana,the larger was S.zayuensi;the abaxial epidermis ranged from 340.42?m2 to1209.99?m2,among which the smaller was S.reducta var.pubescens,the larger was S.unguiculata.2 Cuticular surface and wax ornamentationThe types of cuticular surface and wax ornamentation of Sect.Sorbus are extremely rich.The types of cuticles are mainly smooth or nearly smooth,with randomly oriented stripes,with parallel striae,ridge or with papillae,of which the papillae is only distributed on the abaxial epidermis of plants,such as S.glomerulata,S.hupehensis,and S.hypoglauca;At the same time,it also has smooth,nearly smooth,rod-like,granulate,flake-like,scaly,verrucate,or small processes wax ornamentation.Some plants only have one wax ornamentation,such as S.cibagouensis,S.gonggashanica,S.pteridophylla,etc.;some plants also have multiple wax ornaments,such as S.discolor,S.hypoglauca,S.rufopilosa and so on.3 Stomatal apparatus charactersThe stomata of the plants in the Sect.Sorbus are only distributed on the abaxial epidermis of the leaves,and are composed of two kidney-shaped guard cells and stomata.There are no secondary guard cells.The guard cell poles have no‘T'type thickening structure,which do not sink,and have a single outer stomatal rim and the type of stomatal apparatus are all anomocytic.The difference is that the ornamentation of outer stomatal rim is extremely rich,with a smooth or nearly smooth,rod-like,scaly,granulate,flake-like or small processes,and inner margin of outer stomatal rim has four types:nearly smooth,sinuolate,sinuous and sinuate.The size and density of the stomata among different taxa also have a certain gap.the length of the stomata is 21.41?40.33?m,the width is 16.96?29.20?m,the area is 279.40?928.34?m~2,and the density is 85.50?340.58?/mm~2,the ratio of length and width of the stomatal apparatus is 1.18?1.65.According to the ratio of length and width of the stomatal apparatus is divided into three types:widely elliptic,elliptic and oblong elliptic,of which only S.filipes is oblong.The stomatal traits had no significant correlation with the ploidy.In this study,10 taxa such as S.discolor,S.glomerulata and S.harrowiana were diploid,and 14 taxa such as S.carmesina,S.cashmiriana and S.filipes were tetraploid,the ploidy of 9 taxa including S.amabilis,S.apiculata and S.himalaica have not been reported.The results showed that the stomatal length and density of diploid plants varied greatly,with lengths ranging from 21.41 to34.25?m,and densities ranging from 168.19 to 335.18?/mm~2;The stomatal lengths of tetraploid plant ranging from 32.68 to 40.33?m,the density ranging from 115.48 to 340.58?/mm~2.This indicates that the different ploidy taxa have partial overlap and crossover in the size of stomata,and almost completely overlap in the stomatal density.Therefore,it is not supported to use these traits to infer the ploidy of plants in Sorbus.4 Taxonomic significance of leaf epidermis micromorphologyAccording to the principal component analysis and cluster analysis results of leaf epidermal micromorphological characteristics,leaf epidermal cuticular surface and wax ornamentation,ornamentation of outer stomatal rim,inner margin of outer stomatal rim,stomatal size and leaf epidermal cell shape are important morphological traits for the identification of the species of Sorbus,and a identification key has been compiled from it.A phylogenetic tree constructed based on 20 traits found that these shape features are very obvious for the classification of plant taxa,and can provide a basis for the identification of plant taxa of the compound leaf group.However,the support rate of the classification under the existing group of the Sect.Sorbus is not high,only Ser.Reduetae and Ser.Insignes species come together.