Abstract: Occurring at the southern-most part of Yunnan province of China, the limestone flora of Xishuangbanna is a tropical one and belongs to the part from the northern margin of tropical Asian flora. In comparison with some regional floras from neighbouring areas, it is revealed that the limestone flora has closer affinity to tropical floras. It is also revealed that the similarity coefficient between tropical floras is almost not affected by limestone or non-limestone habitat, while the similarity coefficient between subtropical floras is more affected by limestone or non-limestone habitat. In the relationships with neighbouring floras, the limestone flora shows closer affinity to the floras of Indo-China, SE Yunnan, Guangxi, Hainan, Myanmar, Thailand and Malay Peninsula. It is concluded that the limestone flora of Xishuangbanna has the same ori-gin as the floras of tropical-subtropical Yunnan and Indo-China and is possiblly derived mainly from the "cathaysian flora" in south china but strongly affected by tropical Asian nora.

Key words: Xishuangbanna