Alessandro,
Do the leaves appear in fall or spring?
If spring then you need to know if the leaves have a faint white stripe down the center of the leaves. Without -- I would put it near shaanxiensis (but I doubt it), with -- I would not say it is either chinensis or guangxiensis.
So, I think your plant has fall produced leaves and would be closest to Xalbiflora or Xhoudyshelii.
Aaron