  We study the superfluid to Mott-insulator transition of bosons in an optical
anizotropic lattice by employing the Bose-Hubbard model living on a
two-dimensional lattice with anizotropy parameter $\kappa$. The compressible
superfluid state and incompressible Mott-insulator (MI) lobes are efficiently
described analytically, using the quantum U(1) rotor approach. The ground state
phase diagram showing the evolution of the MI lobes is quantified for arbitrary
values of $\kappa$, corresponding to various kind of lattices: from square,
through rectangular to almost one-dimensional.
