Study On The Systematic Classification Of Subgenus Tsutsusi (Sweet) Pojarkova Of Rhododendron In China

As it is well known , the genus Rhododendron L. is a large one with the number of 1000 species in the world, it is considered as a type of temperate distribution .Since the genus Rhododendron had been established by Linnaeus in 1753,much has been written on the classification of this genus.Because of the collection being in an ever-increasing stream from any place in the world, particularly from China ,more and more new species of Rhododendron have been named ,and at the same time ,problems of systematic classification of Rhododendron are occurring. At the same time,there are same problems occurring in the Subgenus Tsutsusi (Sweet) Pojarkova,for example, some species newly named from China in the recent of 30 years are difficult to be divided ,and whether sect.Brachycalyx Sweet includes Rhododendron tashiroi Maxim. etc. The question now arises: are we to accept the present classification or are we to substitute some other classification in its place? In order to make a clear classification for the subgenus Tsutsusi,a thorough study and a detailed examination of the subgenus Tsutsusi has been made in this paper based on the analysis of ITS sequences ,features of leaf anatomic structure ,features of vessels and characters of morphology.With modern technique of cassification such as molecular marker and plant anatomy,a study on the systematic classification of subgenus Tsutsus of Rhododend -ron in China is made in this paper, in which 74 species and 2 subspecies and 13 varieties and 1 form belonging to this subgenus have been discussed with the conclusions as follows:1.Based on various evidences from the analysis of ITS , features of leaf anatomic structure ,features of vessels and characters of morphology in this paper , Subgenus Tsutsusi (Sweet) Pojarkova of Rhododendro has 74species and 2subspecies and 13 varieties and 1 form in China ; Sect.Tsutsusi Sweet of this subgenus has 69species and2 subspecies and 12 varieties ; Sect.Brachycalyx Sweet of this subgenus has now 5 species and 1 variety and 1 form . In addition , a new arrangement of systemic classification of this subgenus has been offered in this paper.2.Based on ananlysis of ITS,it is considered to be correct that the Subgenus Tsutsusi (Sweet) Pojarkova of Rhododendron is classified into two sections ,namely section Tsutsusi Sweet and section Brachycalyx Sweet.The Sect.Tsutsusi Sweet and Sect.Brachycalyx Sweet are sister groups belonging to Subgenus Tsutsusi (Sweet) Pojarkova. 3.It is right that Rhododendron tashiroi Maxim. is placed in Sect.Brachycalyx Sweet according to the ananlysis of ITS.4. Based on ananlysis of ITS ,the systematic position of Rhododendron schlippenbachii Maxim. is in need of further discussion because of its position shown in the phyletic tree in which it has not clustered with Subgenus Tsutsusi .5.Based on various evidences from the analysis of ITS,features of leaf anatomic structure ,features of vessels and characters of morphology,it is considered to be right that species Rhododendron daiyunicum Tam is treated as a variety of species Rhododendron mariesii Hemsl. et Wils.and and Rhododendron mariesii Hemsl. et Wils. f. albescense B.Y.Ding et G . R.Chen published in 1989 is retained as a form of Rhododendron mariesii Hemsl. et Wils.; Species Rhododendron cinereoserratum is a synonym of Rhododendron mariesii Hemsl. et Wils.; therefore the Sect.Brachycalyx Sweet has now 4 species and 1 variety and 1 form in China .Species Rhododendron tiantangense G .Z .Li is a new combination of Rhododen -dron microphyton Franch ; Rhododendron crassimedium Tam is treated as a synonym of Rhododendron hypoblematosum Tam and Rhododendron rufulum Tam is a synonym of Rhododendron florulentum Tam6.Based on the analysis of the flora of subgenus Tsutsusi Sweet in this paper , some important conclusions have been obtained as follows: China is the center of species diversity of subgenus Tsutsusi and of Sect.Tsutsusi ; but Japan is the center of species diversity of section Brachycalyx .Most of species of subgenus Tsutsusi distribute in China , the number of species of this subgenus is in order as Guangxi> Guangdong>Hunan>Jiangxi>Gui Zhou>Fujian>Sichuan or Yunnan . It is sure that the combination region in Guangxi and Guangdong and Hunan is the center of species diversity of subgenus Tsutsusi in the world .The subgenus Tsutsusi origins from the combination region in Guangxi and Guangdong and Hunan in China , it evolutes directly from the primitive group of subsect. Auriculata .7.Based on the analysis of ITS and paleogeography and fig.XIV , Sect. Brachyca -lyx Sweet probably evolutes from the primitive group of Sect.Tsutsus.Sweet , it evolutes quickly with new characters and form a sister group with Sect.Tsutsus.Sweet which show close connection between these two sections .8.The routes of emigration of Subgenus Tsutsusi (Sweet) Pojarkova coming from its original region are considered as follows : southern and western part of China→ islands of Malaysia→northern part of Philippine ; southern and western part of China→Japan ; mainland of China→Taiwan.9.Discovery(1) A new variety of species : Rhododendron seniavinii Maxim. var. Rhododen -dron shangyounicum R .L. Liu et T. Z.Du,var. nov.(2) A type of idio-cells which is similar to the"cotton"has been found in mesophyll tissue of Rhododendron crassistylum M.Y.He and it is named as"cotton"cell in this paper. It is necessary to discuss what is the function of this type of cells .(3) A special type of pits named"perforation-like plates"is found in the vessels of species Rhododendron rivulare Hand. -Mazz. and Rhododendron . naamkwanense Merr.and Rhododendron.seniavinii Maxim.,it is valuable in evolution and in Classification of Rhododendron , its function and origin is in need to further research .