Abstract: The floral provinciation apparently controlled by climatic zones appeared on the Earth from the Early Carboniferous onwards,forming three floral provinces,i,e.,the Gondwana floral province which represents the southern temporate and/or frigid zones,the Angara floral province which represents the northern temperate and/or frigid zones,and the Euramerican floral province (sensu lato) which represents the tropical-subtropical zones.
With the convergence of the Laurasia and Gondwana continental landmasses in western Tethys during the Late Carboniferous,the Euramerican floras(sensu lato)were differentiated in the eastern and western parts,resulting in the formation of two floral provinces,i,e.,the Euramerican floral province (sensu stricto) in the west and Cathaysian floral province in the east.The differences between the two floral provinces and the origin of the east-west differentiation are probed in this paper on the basis of the ecological characteristics and evolutional stages of the two floral provinces,the reconstruction of palaeotectonic framework and the palaeogeographical environments.It is suggested that the floral differentiation was caused by the east-west climatic differentiation which,in turn,resulted from the plate convergence in western Tethys giving rising to the dry continental climates in the west,while the climates in the east remained to be the humid marine climates.