The morphological structure, osmotic adjustment, stomatal regulation and antioxidative enzymes of mesophilous, xerophilous and super- xerophilous species of Caragana were studied, in order to understand their ecological adaptation mechanisms. The results showed that flat leaves with few green villi were common in mesophilous species, tile-shaped leaves with offwhite villi were common in xerophilous species and tile-shaped or tube-shaped leaves with densely vertical or fallen silky villi were common in super-xerophilous species. Leaf thickness was greatest in super-xerophilous species, less in xerophilous species, and least in mesophilous species. Leaf area, leaf biomass, and specific leaf area (SLA) were highest for mesophilous species, with xerophilous species having lower values, and super-xerophilous species having the lowest values. The thickness-area ratio and length-width ratio in super-xerophilous species and xerophilous species were greater than those in mesophilous species. With these morphological features, the water retention capability was highest in super-xerophilous species, and lower and lowest in xerophilous and mesophilous species, respectively; conversely, light use capability was highest in mesophilous species, followed by xerophilous and super-xerophilous species, respectively. The osmotic adjustment substances content, cytoplasmic ion concentration and osmotic potential of super- xerophilous species were the highest, with those of xerophilous species being intermediate and those of mesophilous species being the lowest. The most obvious differences in osmotic adjustment substances content were that the soluble sugar and inorganic ion contents decreased substantially from super- xerophilous to xerophilous and then to mesophilous species. The leaf total and free water content, leaf water potential, as well as stomatal conductance were highest in mesophilous species, intermediate in xerophilous species and lowest in super- xerophilous species, whereas the bound water content, ratio between bound and free water, peroxidase (POD) and superoxide dismutase (SOD) activity were in the reverse order. Catalase (CAT) activity was highest in xerophilous, intermediate in mesophilous, and lowest in super- xerophilous species. These ecophysiological characteristics resulted in different drought resistance ability and metabolism intensity among Caragana species. Super-xerophilous species had the strongest drought resistance, while xerophilous species had medium drought resistance and mesophilous species had the lowest drought resistance, whereas the metabolism intensity was the highest in mesophilous species, intermediate in xerophilous species and lowest in super-xerophilous species. The diurnal water deficit of xerophilous and mesophilous species was low, and super-xerophilous species had gradually increasing diurnal water deficit from dawn to dusk. Both permeability of plasma membrane and malondialdehyde (MDA) content were greatest in super-xerophilous species, intermediate in xerophilous species, and least in mesophilous species. Free radical content was highest in xerophilous species, with mesophilous and super-xerophilous species having intermediate and lowest values, respectively. These results indicated that although the xerophilous and super-xerophilous species had evolved many morphological and physiological characteristics to cope with the arid environment in desert, their adaptation might still be insufficient. From this study, we can draw two main conclusions: (1) The morphological and physiological characteristics of Caragana species vary in accordance with the environmental conditions of their distribution areas in the Inner Mongolia Plateau. The wide range of variation in morphological and physiological characteristics may be the biological base for the broad distribution of Caragana species in the Inner Mongolia Plateau. With an active metabolism, fast growth and high water consumption, mesophilous Caragana species have strong competitive ability. A low metabolism, economical water use strategy and strong stress tolerance, especially to drought, enables xerophilous and super-xerophilous Caragana species to thrive in harsh environmental conditions. (2) Xerophilous and super-xerophilous Caragana species adjust their cell osmotic potential mainly through accumulating soluble sugars and inorganic ions, which are probably energy-saving adaptation strategies in stressful environments with less productivity.