Abstract: Caiyanghe Nature Reserve in Simao is located at a transitional area from the tropical southern to the subtropical center of Yunnan. Intensive floristic inventory was made in the Nature Reserve. Total 1920 species of seed plants belonging to 836 genera and 178 families were recorded. Orchidaceae with 223 species of 69 genera is the largest family in size in the nature reserve, and other abundant families in species richness are Rubiaceae with 100 species of 37 genera, Compositae with 86 species of 47 genera, Papilionaceae with 82 species of 33 genera, Labiatae with 62 species of 28, Euphorbiaceae with 59 species of 25 genera, Urticaceae with 5 species of 13 genera, Gramineae with 47 species of 34 genera, Lauraceae with 44 species of 12 genera, Moraceae with 44 species of 6 genera, and Acanthaceae with 36 species of 26 genera etc. The areal types at generic and specific levels are analyzed respectively. The tropical elements contribute to 83.3% at generic level and 70.0% at specific level of the flora, of which tropical Asian (Indo-Malaysia) elements contribute to 31% at generic level and 60.0% at specific level. Thus it is obvious that the flora of the Nature Reserve in Simao is of tropical in nature and belongs to Indo-Malesia floristic kingdom. As the nature reserve is located at a transitional area of tropical south to subtropical Yunnan, many tropical plants reach up their northern limit of distribution here. Therefore, the flora of Caiyanghe Nature Reserve is transitional toward the subtropical flora of Yunnan. Based on comparison to the flora of Xishuangbanna in southern Yunnan and the flora of Wuliangshan in center Yunnan, it is revealed that Tropical Asian elements reduced conspicuously, while Northern temperate and Eastern Asian elements increased conspicuously in the transition from tropical Asian flora to Eastern Asian flora in southern Yunnan.

Key words: seed plant flora, geographical elements, Caiyanghe Nature Reserve, Yunnan