Abstract: The gametophyte development and apogamy of the fern Cheilosoria chusana were studied using microscopy. The spores, with echinate ornamentation, are tawny, trilete, circular triangle in polar view. The spores germinate about 15-20 d after being sowed. The spore germination pattern is the Vittaria-type. The filaments generally have 3-5 cells. The plates form by division of the apical cell or intercalary cells of the filament. The gametophyte forms the meristematic tissue in the apical or lateral region of the plate, and grows into prothallus in about 2 months after being sowed. The development of the prothallus is the Ceratopteris-type. The antheridia appears in the irregular plates. The antheridia are numerous. The repeat cultures show that no archegonia occurs in the adult prothallus. The prothallus can produce sporophytes through apogamy. The filament branches are easily formed, whether in the stage of filaments, plates or prothallus. One spore of C.chusana can develop into caespitose gametophyte (cluster) with filaments or filamentous plates in appropriate culture conditions. It is proved that the clusters of gametophyte are in favor of adaptability to the dry environment to single prothallus.

Key words: ferns, Cheilosoria chusana, gametophyte development, gametophytic cluster, apogamy