Hedysarum fruticosum var. lignosum is a superior species in the sand dunes of Hunshandake Sandland. Exploring the photosynthetic characteristics of this species will be helpful to reveal the adaptive mechanisms of the pioneer species in the sandy environment. The photosynthetic characteristics of H. fruticosum var. lignosum are monitored and compared with those of Salix gordejevii, a typical C₃ species co-existing with H. fruticosum in semi-fixed or fixed sand dunes. The maximal photosynthetic rate (P_max) and water use efficiency of H. fruticosum are approximately one times higher than that of S. gordejevii. H. fruticosum could endure high light and temperature at noon and has a high light saturation point and a low light compensation point. Except Ribulose-1.5-bisphosphate carboxylase (RuBPcase), the activities of photosynthetic carbon assimilation enzymes, such as phosphoenolpyruvate carboxylase (PEPcase), NAD-malic enzymes (NAD-ME), NADP-malic enzymes (NADP-ME), NAD-malate dehydrogenase (NAD-MDH), NADP- malate dehydrogenase (NADP-MDH), and pyruvate phosphate dikinase (PPDK), in H. fruticosum are at least four times greater than that in S. gordejevii, it is suggested that H. fruticosum might have a C₄ photosynthetic syndrome. However, the stable carbon isotope analysis reveals that H. fruticosum has the δ¹³C value of -23×10^-3, which is closed to that of C₃ plants. Therefore, it is likely that H. fruticosum is either a C₃-C₄ intermediate species, or a C₃ species displaying C₄ metabolic characteristics in the habitat of sand dune. The involvement of C₄ metabolism in H. fruticosum might account for its greater efficiencies for photosynthesis and water use, and allows H. fruticosum to colonize the shifting sand dune with high temperature, light intensity, and water stress.