The spin dynamics of a canted antiferromagnet with a quadratic spin-wave dispersion near q =0 is shown to possess a unique signature. When the anisotropy gap is negligible, the spin-wave stiffness D sw ͑q , B͒ = ͑ q − B͒ / q 2 depends on whether the limit of zero field or zero wave vector is taken first. Consequently, D sw is a strong funtion of the magnetic field at a fixed wave vector. Even in the presence of a sizable anisotropy gap, the field dependence of the extrapolated q = 0 gap energy distinguishes a canted antiferromagnet from a phase-separated mixture containing both ferromagnetic and antiferromagnetic regions.