Abstract: Morphology of the leaf costa of 24 Polytrichaceae in China were studied by measuring with strong acid.The length and width of cells,the thickness of cell walls and numbers of pit fields of the leaf costa were measured.The results showed that variations of the cell structure of Lyellia is lower,while the variations of genus of Polytrichum,Pogonatum and Oligotrichum are higher among different species of genus Lyellia,Polytrichastrum,Pogonatum and Polytrichum can adapted the drought environment more easily than Microdendron,Oligotrichum,Atrichum according to the numbers of pit field of cells.