SNe Ia play key roles in revealing the accelerating expansion of the universe, but our knowledge of their progenitors is still very limited. Here we report the discovery of a rigid dichotomy in circumstellar (CS) environments around two subclasses of SNe Ia as defined by their distinct photospheric velocities. For the SNe Ia with high photospheric velocities (HVs), we found a significant excess flux in blue light 60100 days past maximum, while this phenomenon is absent for SNe with normal photospheric velocity. This blue excess can be attributed to light echoes by circumstellar dust located at a distance of about (12)1017 cm from the HV subclass. Moreover, we also found that the HV SNe Ia show systematically evolving Na
iabsorption line by performing a systematic search of variable Na iabsorption lines in spectra of all SNe Ia, whereas this evolution is rarely seen in normal ones. The evolving Na iabsorption can be modeled in terms of photoionization model, with the location of the gas clouds at a distance of about 21017 cm, in striking agreement with the location of CS dust inferred from B-band light-curve excess. These observations show clearly that the progenitors of HV subclass are likely from single-degenerate progenitor system (i.e., symbiotic binary), while the NV subclass may arise from double-degenerate system.