  We study the phase diagram of spin-one polar condensates in a two dimensional
optical lattice with magnetic anisotropy. We show that the topological binding
of vorticity to nematic disclinations allows for a rich variety of phase
transitions. These include Kosterlitz-Thouless-like transitions with a
superfluid stiffness jump that can be experimentally tuned to take a continuous
set of values, and a new cascaded Kosterlitz-Thouless transition, characterized
by two divergent length scales. For higher integer spin bosons S, the thermal
phase transition out of the planar polar phase is strongly affected by the
parity of S.
