Leaf Characters Of Sorbus Section Sorbus From China And Their Taxonomic Significance

The genus Sorbus L.(Rosaceae,Maloideae)shows its center of diversity and distribution in China.The plants in this genus shows high garden value for their flowers,leaves,fruits and trunks,as well as high medicinal value,edibleness and timber value.The genus contains Sect.Sorbus,Sect.Aria and Sect.Micromeles,in which Section Sorbus shows more difficulties in classification.In our research,leaf characters including leaf morphology and leaf venation characters of 31 species and 7 varities of China were observed and examined to provide extra taxonomical evidence for Section Sorbus.The results are as follows:1.Leaf morphology characters.The variation range of leaf morphological characteristics and pubescence of Sect.Sorbus showed greatly huge.The length of pinnate leaves together with rachis of different taxa varied from 4.61 to 26.93 cm.There was deep or slightly shallow groove on the rachises adaxially,which sometimes showed slightly narrowly winged.The numbers of leaflets per pinna varied from 3 to 17.The intervals between leaflets varied from 4.04 to 27.46 mm.The length of petioles varied from 6.72 mm to 66.49 mm.Central leaflet varied from 10.05×4.36 to 180.52×36.30 mm which could be divided into three levels: Microphyll(25~225 mm2);Notophyll(225~2025 mm2);Mesophyll(2025~4500 mm2),areas of central leaflets varied from 30.9 to 5179.05 mm2.The angle of leaflets’ base showed obtuse or acute.The number of teeth per side of leaflets varied from 2 to 42,which mostly were sharply serrate or seldom obtuse.Serrate only at apex or base of leaflets.The pubescence on rachises and leaflets showed smooth,white hairs,brown or brown to reddish-brown hairs.The results of One-way ANOVA analysis showed that the number of leaflets per pinna,leaflet intervals,leaflet length(means the central pair leaflets,the same below),leaflet width,leaflet area,leaflet perimeter,the ratio of leaflet length to width,the number of teeth and the ratio of length of the part of leaflet with teeth to leaflet length showed significantly different in interspecies(α=0.01),which could be used as taxonomical characters.Pearson correlation analysis results show that most of the leaf morphological characteristics are not independent to each other,some traits were confirmed to show very high correlation(|r|>0.8,P﹤0.01),such as number of leaflets per pinna showed significantly negative correlation with terminal leaflet width and leaflet intervals.Leaflet length showed significantly positively related to some characters such as terminal leaflet length,terminal leaflet width,leaflet intervals,the length of the part of leaflet with teeth,leaflet width,leaflet area,leaflet perimeter and the number of teeth.Some characters like the ratio of terminal leaflet length to width,the ratio of terminal leaflet length to width,the base angle and the ratio of length of the part of leaflet with teeth to leaflet length were found to be relatively independent.2.Leaf venation characters.The results showed that the venation fabric of all taxa was found to be semicraspedodromous pinnate,the higher order venation can be resolved to the sixth and marginal ultimate venation formed incomplete.But some other characters differed sharply such as the primary veins size,the number of major secondary veins and its angle to primary vein,intersecondary vein fabric,tertiary vein fabric,areolation development,branch situation of veinlets and vein density,which can be good recognition characters in this section.The primary veins size showed to be massive,stout or moderate.The number of major secondary veins varied from 4 to 27.The angle between major secondary veins and primary vein narrow acute,moderate acute or wide acute and showed three types of relatively uniform,decreasing proximally or increasing proximally.Intersecondary vein fabric simple or compound.The frequency can be more or less than one vein per intercostal area.Tertiary veins fabric showed opposite percurrent or mixed opposite and alternate percurrent.Areolations showed poor,moderate or good development.The veinlets showed mostly unbranched,one branched or two and more branched.Vein density varied from 4.77 to 9.63 mm/mm2.The results of One-way ANOVA analysis showed significantly different in number of major secondary veins,intervals between major secondary veins and vein density in the interspecific(α=0.01).3.The taxonomical significance of leaf features and leaf venation characters.The results of cluster analysis showed that the 38 taxa could be divided into two branches at the gower’s coefficient of 0.45,the larger branch could be divided into three categories again at the gower’s coefficient of 0.30,so that the 31 varieties and 7 varieties tested could be divided into four branches as a whole.The results of principal component analysis and leaf venation analysis showed that leaf venation characters including intervals between major secondary veins,areolation development,branch situation of veinlets and leaf features including the wings of rachises,number of leaflets per pinna,leaflet area and the distribution and color of pubescence on the surface of leaflets abaxially were important,while intersecondary vein fabric and tertiary vein fabric were key characters to differentiate these species.Accordingly,an identification key to recognize and differentiate species of Section Sorbus was established.To sum up,the study results of leaf characteristics including morphology and venation characteristics could provide references for the classification and identification of Section Sorbus,but couldn’t support the existing classification systems well.