Emmenopterys henryi, an endemic species in China, has been one of the grade II national key conservation rare and endangered plants. The spectra of stem and leaf of Emmenopterys henryi sampling from seven different geographical populations were determined by Fourier transform infrared (FTIR) spectrometry with OMNI-sampler directly, fast and accurately. A positioning technology of OMNIC E. S. P. 5. 1 intelligent software and ATR correction was used. It was scanned for the background before the determination of every example. The peak value and absorbance were ascertained using a method of baseline correction in infrared spectra. Based on the indices of wave number-absorbance from 721 to 3 366 cm(-1), the differences of these infrared spectra were compared by the methods of principal component analysis (PCA) and cluster analysis. Results showed that there were some differences in FTIR spectra between stem and leaf of Emmenopterys henryi, so it was better to study the diversity of different geographical populations through using the leaf, for which the distance coefficient of clustering analysis plot and the position relationship of principal component analysis three-dimensional plot of the seven populations were bigger. Being far away from others populations, the infrared spectra of Emmenopterys henryi in Dapan Mountain and Gutian mountain had special characteristics, indicating significant diversity. At the same time, the infrared spectra of Jiulong Mountain, Wuyan Mountain and Songyang populations had their own characteristics. There were no significant difference in the position relationship of three-dimensional plot and distance coefficient of clustering analysis plot, showing that the chemical compositions of these three populations were of little difference, and the diversity differentiation was not remarkable. However, there were some significant differences in populations' diversity between Fengyang Mountain and Wencheng. It was indicated that the chemical composition of Emmenopterys henryi was affected by the special geographic positions and environment conditions. In a word, the remarkable differences in the chemical compositions of Emmenopterys henryi populations were consistent with their geographic distance far and near. The results also showed that there was good correspondence between the position relationship of PCA three-dimensional plot and distance coefficient of clustering analysis plot of the samples based on the indices of wave number-absorbance of FTIR and their geographic distance relationship. Therefore, FTIR can be used widely for studying and protecting the rare and endangered plants. It is not only provides the theoretic base of community ecology and ecosystem ecology of Emmenopterys henryi, but also has important theory and realistic meaning for exploring the mechanism of species endangerment, protecting and proliferating the populations of Emmenopterys henryi.
