Abstract: Caldesia grandis Samuel.is an endangered aquatic plant which was once considered to be extinct in mainland China and was recently found in a bog in a mountainous region of Hunan Province.Acytological study on the species basing on the materials from the newly found locality is reported here.The karyotypical analysis reveals that this species has a chromosome number of 22 and contains high-level asymmetrical chromosomal complements.Combining the results of cytological and paleontological studies on some closely related species reported by earlier researchers,it is suggested here that the genus Caldesia is probably the most advanced group in Alismataceae.