Ranalisma rostratum Stapf is a rare and endangered species．  This paper deals with the development of its male and female gametophytes and probes the relationship between the process of reproduction and the cause which made this species endangered．  The meiosis of  microspore mother cells is successive cytokinesis and  the microspore tetrads are isobilateral．  Pollen grains are 3-celled when shed．  The ovule is anatropous，bitegmic and tenuinucellate．  The micropylar dyad cell usually desenerates soon after its formation，  and the chalazal dyad cell develops into a Allium type embryo sac．  During the development of embryo sac both polar nuclei are respectively located at the two ends of central cell，and they maintain this situation until the micropylar polar nucleus takes part in fertilization．  Features of the embryo sac of Ranalisma rostratum Stapf are discussed．