Abstract: Species diversity of the endangered aquatic fern Ceratopteris pteridoides community at Hubei Longgan Lake national wetland nature reserve in China were surveyed using sample plot and α－diversity index. The main results are as follows：there were 11 plant species belonging to 10 families and 10 genera in the community in 2011，among which Zizania. Caduciflora， Hydrochai rsdubia，Eichhornia crassipes，Polygonum hydropiper，Ceratophyllum demersum and Lemna minor were dominant species. The vegetation was called Zizania caduciflora-Hydrochai rsdubia Ass. α－diversity index analysis revealed that Simpson index （D），Shannon-Wiener diversity index （H′），and Pielou evenness index（J）were 0. 846、 1. 939 and 0. 809，respectively，indicating low levels of spe? cies diversity at the community. Human disturbance might be the main factor responsible for the reduction of aquatic vegetation and biodiversity. Both establishing conservation spots and changing spots conservation are two important conservation strategies of the species.

Key words: Longgan Lake, national wetland nature reserve, Ceratopteris pteridoides, endanger, species diversity