Abstract: Different geographical environments lead to different mechanisms of plant ecological adaptation. This comparative study showed that the leaf microstructure and submicroscopic structure of Adiantum flabellulatum, growing in Karst and non-Karst areas, varied widely. The leaf in the Karst area was isolateral and had closely arranged mesophyllous cells. The more developed vascular system can favor water absorption in a dry environment. On the contrary, the leaf grown in the non-Karst area was bifacial, with loosely arranged mesophyllous cells and an undeveloped vascular system. Scanning electron microscope revealed that the leaf epiderm in Karst areas has many culticular spines, and the basal part of the culticular spines was extremely expanded. Further research revealed that the basal part of the culticular spines was shrunken when the leaf was devoid of water in a vacuous environment, which indicated that the culticular spine has the function of supplying water in a drought environment.