Abstract: The Jiuwan Mountains，situated in the middle of northern Guangxi，South China(25°10’～25°25’N，108°27'E)，is a transitional region between the Holarctic flora and Paleotropical flora．Its main vegetation is subtropical evergreen broad-leaved forests consisting of the Lauraceae，Teaceae，Fagaceae and Magnoliaceae．The highest peak of the mountains is 1693 m above sea level，and its bottom is only 170 m．   In 1931，H．Reimers first reported the mossflora of Guangxi titled“Beitraege Zur Mossflora China I”．Four years later，Edwin B．Bartram published“Additions to the mossflora of China”．Hu Sun-si(1981)reported twenty-five species of mosses in Guangxi in  “Preliminary observation on bryophytes in the evergreen broad-leaved forest of Huaping Forest Region in Guangxi”．Up to then reported were about 25 families，43 genera and 62  species of mosses in Guangxi．   In 1989，Li Zhen-yu，Long Guang-ri and Zhang Can-ming made the first botanical expedition to the mountains and about 500 packages of bryophytes were collected there．One  year later，Wang Mei-zhi，He Xiao-lan and the first author of this paper made bryophytic  survey in the mountains，and about 1350 packages of bryophtes were collected there．From  a11 the above specimens，35 families，101 genera and 189 species of Mosses are identified． According to “The areal-types of Chinese genera of seed plants” by Wu Zheng-yi，ten type of the mossflora of the Jiuwan Mountains are recognized: Cosmopolitans ( 8 families and 9 genera ), Pantropical elements( 7 families and 8 genera ), Paleotropical elements (4 families and 4 genera), Tropical Asian to African elements (4 families and 5 genera), Tropical Asian elements (19 families and 33 genera), North Temperate elements (9 families and 17 genera), East Asian ＆ North American disjunctive elements (6 families and 6 genera), Temperate Asian elements (4 families and 4 genera), East Asian elements (71 species), Endemic to China (5 species). Totally, the East Asian elements are the most important ones (39.33%), then the tropical and subtropical elements (38. 20%) are also abundant, and the temperate elements (18.54%) are the third one. For considering the relationships between the mossflora of the Jiuwan Mountains and those of the neighbouring regions, the authors selected five regions around the Mountains. The similarity coefficient of moss genera between the Jiuwan Mountains and the Jinfu Mountains, east Sichuan, is 60. 68% ,and that of moss species is 36.87% . The similarity coefficient of moss genera and species between the Jiuwan Mountains and the Wuyi Mountains are 69. 86% and 39. 57% respectively, higher than those of the other mountain regions. Comparing the mossfloras of the Jiuwan Mountains and the Jianfeng Mountains, there are fourty species commonly, among them thirty-two species are tropical elements which clearly show the close affinity to the tropical mossflora. The similarity coefficient of moss genera and species of the above two mountain are 57.29% and 29.63% rsepectively. Due to the influence of the Himalayas, the tropical elements of Xishuangbanna are different from the Jiuwan Mountains and the Jianfeng Mountains. Floristically, Shennongjia is situated in the transitional region between West and East China, and the similarity coefficient of moss genera and species between the Jiuwan Mountains and Shennongjia are 57.29% and 33.13%.   East-Asiatic endemic genera of the bryophytes are regarded as “Tertiary fossil plants” which enjoy a warm and moist environment. They are mainly limited to temperate and subtropical region. Though there are some species of East-Asiatic element in Xishuangbanna,East-Asiatic endemic genera so far have not been found. There are two genera of East-Asiatic endemic genera of the bryophytes in Jianfengling belonging to tropical region. Nine of East-Asiatic endemic genera of the bryophytes have been recorded in Mt. Jinfu, and show the characteristic of overlapping distribution between Eastern and Western.   Topographically, the Jiuwan Mountains is located at the Southeast of the Yunnan-Guizhou plateau, the edge of second step of China, so far four East Asiatic endemic genera, Taiwanobryum, Pilotriopsis, Meteoriella and Neobarbella have been found. Among them the former two genera are distributed in Japan and the Philippines, however, Meteoriella is found in Nepal and Japan, as well, it was widely recorded in South of Yangtze River and at 2000 meters above the sea level of the evergreen forest in Southeastern Xizang(Tibet), China. Neobarbella occurs in Sikkim, India, the Philippines, Indonesia and Japan, and China is recognized as the distribution centre of this genus. Generally, the above data show that the East Asiatic endemic genera of mosses are evidently influented by the Himalayas. In the Jiuwan Mountains, it is worth to notice that there are about 7% of the tropical species of mosses, such as Syrrhopodon flamme-nervis, Hookeriopsis geminidens, Pterobryopsis crassicaulis and Garovaglia plicata , which clearly indicate the close relationships of the mossflora of Mt. Jiuwan with the tropical elements. However, some tropical mosses, such as Pyrrhogonium spiniforme and Chrysocladium retrorsum, which are found at about 1000 meters above the sea level, also distribute to the South of Yangtze River. The geological data showed that the formation of the South China Sea was the very important event happened in South China in Tertiary. Hainan Island, as one of the migration route with South Asia and South Hemisphere, connected with the Asia continent until the late tertiary. Before that period of time, the Jiuwan Mountains was under the control of the tropical and subtropical climate with Xishuangbanna and Taiwan. Owing to the submergence of Qiongzhou Strait, Hainan Island became an isolated island, then the South Sea gradually formed. A series tropical species occuring in the Jiuwan Mountains might be the evidence of the migration between Laurasia and Gondwana ancient continent.   Several moss genera, Garovaglia , Oedicladium , Pterobryopsis , Leucoloma , Dicranoloma and Callicostella, occuring both in North and South Heimephere, are found in the Jiuwan Mountains now. They might show the bryoflora relationships between the Jiuwan Mountains of South China and Africa, Central and South America. In fact, South America connected with Africa before Jurassic, and the Pacific Ocean and Atlantic Ocean were not so broad as right now.   The ordination method was used for calculating the figure of two dimensional arrangement, the mossflora of the Jiuwan Mountains is very close to that of the Wuyi Mountains. However the typical tropical mosses occuring in the Jiuwan Mountains have not been found in the later mountain region. The Wuyi Mountains, the natural defence for South China, is recognized as the boundary line between Central subtropical and South subtropical region in China. While the mossflora of the Jiuwan Mountains is represented the tropical relationships, but its subtropical elements are still abundant.   Depending on the quantitative and qualitative analysis, the authors consider that the mossflora of the Jiuwan Mountains represents the transitional characteristic from tropical region to subtropical region in South China, and in Guangxi the boundary line between them might be set at the south of the Jiuwan Mountains.Decontaminated thi