Abstract:The morphological and anatomical features of fruit,seed and seedling development of Ottelia alismoides were observed in the paper,using the morphological observation and GMA sections and inquire into the structures adapted to the water environment in the ontogenetic development of O.alismoides.The results showed:(1)The O.alismoides fruit enveloped by spathe usually have six carpels and their edges do not connect each other completely in the center of fruit and laminal placentation.The young fruit developed above the water was pulled by the carpopodium into water to mature.The seed is with hairs and its shoot apex develops before root apex.The hypocotyl develops unicellular hairs before the radicle differentiates,and then the radicle develops into primary root and the adventitious root formed in the leaf node.The pericarp and mesophyll are vascular bundles composed of a few cells and well-developed air cananls.The epidermal cells of the leaf have no cuticle and their outer walls are bulging and mesophyll is with less cells.All these features of the species are adapted to the water environment.(2)The authors observed that some features of the species (i.e.,seed has no endosperm;the starch grains are rich in hypocotyl,which offer the nutrient for its development;both primary and adventitious roots have root hairs) could be also found in Sagittaria sagittifolia and Alisma plantago-aquatica of Alismataceae.The study showed the close relationship between two families Hydrocharitaceae and Alismataceae.