Systematics Of Ser. Albescentes Ling (Compositae-Aster)

Ser.Albescentes Ling belong to Aster Compositae. Traditionally,it belong to Aster, is a very natural monophyletic groups. But the species and the varietas in the Ser.Albescentes Ling is very complicated with unclear circumscription. The complex is unstable and variable characters, which make it one of the most problematic groups in Compositae.The aim of the present study is to elvaluate the separate genus status of Ser.Albescentes Ling,and to make a taxonomatic revision based on evidence from macromorphology, anatomy, micro-characters,cytology and molecular study. The main results are summarized as follows: 1. Macromorphological analysisOn the basis of examination of herbarium specimens and field observations, the variation pattern of all major macromorphological characters in Ser.Albescentes Ling were analyzed. Their taxonomic significance was re-evaluated. The results show that the vein,achene, the crosscut of lamina, the ratio of ligule and tube are key characters to specific classification within these Ser.Albescentes Ling. However, the shape of leaves and density and shape of hair are greatly variable within a species and are of little significance in specific classification.The characters of achenes are very similar in Ser.Albescentes Ling, and there is only a little different.These different can be seen the type of achene, the column type and the light flat type. 2. CytologyThree species and two variations, including Aster megaphyllus, Aster argyropholis, A.lavandulaefolius and the other two variations of A..albescens,were cytologically investigated. All of these were reported for the first time. In view of the decrease in symmetry, we can reach a conclusion that the Ser.Albescentes Ling is evolutionary advancement.3. Molecular systematicsIt must be acknowledged that there is a series of resemblance of flower between the Ser.Albescentes Ling and the others of Aster. But the specificity of Ser.Albescentes Ling is also manifest. For the data of the system tree of ITS and TrnH, we can clearly seen that the branch of Ser.Albescentes Ling is rather isolated.4. The result of the systematics of Ser.Albescentes LingSer.Albescentes Ling have a series of particular characters that was remarkably differ from the groups of other Aster. This particular characters including that it is a wood plants, the featheriness leaf vein, the ratio of ligule and tube is mostly between 1-2, the primary vein is obviously embossmented in the back of leaf and have remarkable constriction with it, stomatal complex is also embossmented in the back of leaf; the decrease in symmetry of chromosome and so on. Besides, the ITS sequence shows that the Ser.Albescentes is a rather isolated branch in the Aster. Therefore, all of the evidence figured that the Ser.Albescentes should be eliminated from the Aster.5. Taxonomic revisionBased on the above results, Ser.Albescentes Ling is taxonomically revised. The altogether 9 species are recognized. The are A. albescens, A.fulgidulus, A.argyropholis, A.hypoleucus, A.polius, A.lavandulaefolius, A.motuoensis, A.megaphyllus, A. yongshengensis and A. brevifolius Each species is described and their distributions are mapped. Following phenology, habitat preference, and interspecific relationships are also discussed.