Abstract: Identification of C4-photosynthetic pathway and their florology and eco-geography were studied in Inner Mongolia of China according to the stable carbon isotope ( δ13C) contents and some related literatures. The total number of C4 plants in the region was 125 species, belonging to 12 families and 57 genera which reached to 5.4%, 9%, and 8.4% of total species, families and genera respectively in Inner Mongolia area. Most of the C4 plants (82.4%) came from Poaceae, Chenopodiaceae and Cyperaceae families. Based on the above features, the authors have analysed the characteristics, such as life form, water ecotype and distribution, of C4 species in Inner Mongolia. Finally, the relationship between distribution of C4-photosynthesis and some environmental factors in determining C4 plant distribution were also discussed. Most of the C4 species were highly concentrated to a few families and genera, which could be contributed to their own hereditary features. The life form of most C4 species was found to be annual herbs, possibly owing to their narrow origin fam ilies or genera. The water ecotypes of C4 plants in this area was shown to be drought, indicating that such species preferred to heat and could resist drought habitat well.

Key words: C4 plant, Life form, Water ecotype, Geographical element of flora, Ecological distribution