Abstract: The seedlings leaves of Ammopiptanthus nanus and seedlings and adult leaves of Ammopiptanthus mongolicus were studied by paraffin sectioning, and their structures were analyzed by optical microscopy. The purpose of this study is to explore the ecological adaptation mechanism of the leaves of the plant of the genus Ammopiptanthus in the arid environment. The variance analysis method was used to compare the differences of the indexes, and the correlation between the indexes was analyzed by the Pearson's correlation coefficient method. The results showed that:(1) Seedling leaf thicknesses were no significant difference between A. nanus and A. mongolicus; Thickness of seedlings leaf cuticle, upper and lower epidermis and palisade tissue of A. nanus were significantly higher than those of A. mongolicus; sponge tissue thickness and the diameter of the main vein of A. nanus seedlings were significantly less than A. mongolicus. The leaf thickness, cuticle thickness, palisade tissue thickness and main vein diameter of adults A. mongolicus were significantly higher than those of seedlings. The thickness of the upper and lower epidermis and the thickness of sponge tissue were all smaller than those of seedlings. (2) the thickness of palisade tissue was positively correlated with leaf thickness; the thickness of lower epidermis, the thickness of stratum corneum, and the thickness of sponge tissue were not significantly correlated with leaf thickness. In order to better adapt to the environment, the drought resistance of leaf of A. nanus is stronger than A. mongolicus, and drought resistance of adult A. mongolicus is better than that of seedling leaves. The thickening of the leaves of the genus Ammopiptanthus is mainly realized by the thickening of the palisade tissue.

Key words: Ammopiptanthus monglicus, Ammopiptanthus nanus, leaf anatomical structure, xeromorphic indexes, drought resistance