Abstract:The formation and development of the spores and their ornamentations of the fern Asplenium sarelii(Aspleniaceae) were studied by means of transmission electron microscope (TEM). The results were as follows: ①The development of the sporangium of A.sarelii belongs to Leptosporangiate-type. ②The exospore is smooth, with a thickness of about 0.8-1.1 μm in the distal surface and 1.4-1.8 μm in the proximal surface. ③The perispore, with a thickness of about 4-5 μm, can be distinguished into an outer perispore and an inner perispore. The inner perispore is closely associated with the outer surface of the exospore. The inner perispore has cylinder, tuberculate, and verrucate projections on the out surface. The outer perispore uplifts and forms the lophate ornamentations. Simultaneously, cavities are formed inside the outer perispore and the fins are formed outside the perispore. ④The formation processes of the exospore and perispore of Asplenium-type spores are similar with that of Dryopteris-type spores. ⑤The maturity degree of the spore during development is a key factor for studying the spore palynology. Only the matured spore possesses stable spore ornamentation.