There are 16 Caragana species in Inner Mongolia Plateau and they are found over a vast area of land (from the east in Hulunbeier grassland, 125 E, to the west in Alashan desert, 98 E), which varies with climate and vegetation along longitudinal series. The number of species within the genus Caragana increases following the environmental gradient from the east to the west, or from forest to grassland and to then desert. In order to explore the biological basis for the geographical distribution of these Carag...