Let G be a semisimple Lie group with no compact factors, K a maximal compact subgroup of G, and \Gamma a lattice in G. We study automorphic forms for \Gamma if G is of real rank one with some additional assumptions, using a dynamical approach based on properties of the homogeneous flow on \Gamma\backslash G and a Livshitz type theorem we prove for such a flow. In the Hermitian case G=SU(n,1) we construct relative Poincaré series associated to closed geodesics on \Gamma\backslash G/K for one-dimensional representations of K, and prove that they span the corresponding spaces of holomorphic cusp forms.