Abstract:Development of aposporous embryo sac, embryo and pseudogamy were studied in tetraploid Paspalum distichum. In most cases, shortly after the megasporocyte developed into a tetrad, it began to deteriorate, meanwhile several nucellar cells became active and enlarged, Normally, 1-3 nucellar cells developed into mature aposporous embryo sacs characterized by 1 egg cell and 2 polar nuclei. The egg cell could spontaneously develop into proembryo prior to anthesis, whereas polar nuclei were involved in pseudogamy to develop endosperm after heading and pollination. When several aposporous sacs occurred in an ovule, only the sac near the micropyle developed endosperm while the other sacs did not. The frequency of twin-embryo seedlings geminated from mature seeds was low. Few sexual 8-nucleus embryo sacs as well as both sexual and aposporous sacs in the same ovule were found. It is suggested that the tetraploid P. distichum is considered to be a facultative apomict reproduced by apospory.