A previously unknown species of the North American leafhopper genus Flexamia, F. whitcombi sp. n., is described from pinebarren smokegrass (Muhlenbergia torreyana (Schult.) Hitchc.), a state-listed threatened grass in the New Jersey Pine Barrens. The serrata species group, to which it belongs, is redefined and a key to the species of the group is provided. This is the first reported insect association with M. torreyana.