Abstract: Investigation on variation of fruit morphology development of water caltrop（Trapa natans L.） was carried out for two-horn-water caltrop and four-horn-water caltrop. It indicated that①The variation rate of fruit morphology of two-horn-water caltrop was 36.9%. Among them, that of the number of top horn pose was the highest, which was 36.9%. That of the number of fruit with acutangular horn was small, which was 3.1%. The variation rate of fruit morphology of four-horn-water caltrop was 45.1%. Among them, those of the number of fruit with acutangular horn and the position of fruit with acutangular horn were the highest, which were 26.5%. The second, that of the pose of horn in the middle was 18.7%. The third, that of top horn pose was the smallest, which was 0.7%. ②Making a comprehensive survey for two-horn-water caltrop and four-horn-water caltrop, the variation rate of fruit morphorlogy was 41.0%. Among them, that of top horn pose was the highest, which was 18.8%. The second, that of the pose of horn in the middle was 18.6%（four-horn-water caltrop）. Those of the number of fruit with acutangular horn and the position of fruit with acutangular horn were the smallest, all of which were 14.8%. No change in the number of fruit horn was observed in either two-horn-water caltrop or four-horn-water caltrop.

Key words: water caltrop（Trapa natans L.）, morphology, development, variation