Abstract: The mating system of Ranalisma stapf., an endangered aquatic species,was studied synthetically.The results are as follows:Pollen grains and stigmas were relatively smooth.Glandular cells occurred in flowers but not well developed.Pollen germination showwed a higher level(71.6%)before flowering and a rapidly declining 1 hour after flower opening.Pollen -ovule ratio was a quite low value(P/O=106).Floral syndromes were suitable to the mating habits of pre- anthesis cleistogamous.In natural or experimental populations,inter-flower pollination by insect were not observed,but inra-flower pollination were made by some small-size insects(Tripidae).

Key words: Ranalisma rostratum, Mating system , Outcrossing rate