Abstract: Pteridaceae is the fourth fern family in China with respect to species richness, which contains 18 threatened species with various ecotypes including terrestrial, lithophytic and aquatic. Understanding the status of endangered Pteridaceae species with different ecotypes can provide useful information for the conservation of the endangered fern species. We investigated the location and size of natural populations of three endangered Pteridaceae species on the Chinese mainland: Adiantum nelumboiddes and Aleuritopteris grevilleoides, both terrestrial or lithophytic, and aquatic Ceratopteris pteridoides. We compared their climatic adaptability with 19 bioclimatic factors from WorldClim and found their dominant climatic factors. We simulated their potential distribution patterns using MaxEnt model under current climate scenario. Ad. nelumboiddes, is sensitive to the temperature annual range (bio7) and confined in the canyon of the Yangtze River from Zhongxian County to Wanzhou District of Chongqing City. Its natural population size is extremely small, with a total of about 500 individuals. Since it has high medical and economic values, the natural population has been under the pressure of serious human disturbance. Al. grevilleoides prefers warm winter (bio11) and low annual precipitation (bio12) and is found in Dayao County of Chuxiong Autonomous Prefecture and Luquan County of Kunming City in the north of Yunnan Province. The model simulation showed that Yuanmou, Yongren and Yongsheng in Yunnan Province which belonged to the dry warm valleys of the Jinsha River basin, were highly suitable areas for Al. grevilleoides. Population size of C. pteridoides was much larger than other two species, which is widely distributed in the shallow wetlands of the middle and lower reaches of the Yangtze River as well as the in the reed marsh at the lakeshore of Weishan Lake in Shandong Province. We proposed suggestions for the conservation of these three species.

Key words: ferns, Aleuritopteris grevilleoides, Adiantum nelumboiddes, Ceratopteris pteridoides, species distribution model, climatic factor, biological conservation.