The (1,1)-symplectic property for f-structures on a complex Riemannian manifold M is a natural extension of the (1,2)-symplectic property for almost-complex structures on M, and arises in the analysis of complex harmonic maps with values in M. A characterization of this property in combinatorial terms is known only for almost-complex struc- tures or when M is the classical flag manifold F(n). In this paper, we remove these restrictions by considering an intersection graph defined in terms of the corresponding root system. We prove that the f-structure is (1,1)-symplectic exactly when the intersection graph is locally transitive. Our intersection graph construction may be helpful in characterizing many other Kahler-like properties on complex flag manifolds.