Functional diversity is generally regarded as the constituent of biological diversity that considers how the species functional traits affect ecosystem processes. Due to its ecological relevance, a number of indices of functional diversity have been proposed to date based on distinct objectives and motivations. Such proliferation of indices can be at least partially overcome by a more fundamental mathematical approach. In this paper we propose an intrinsic ordering approach for abundance-weighted measures of functional diversity that is similar to the Lorenz curves used by ecologists for ordering evenness measures. We then discuss the relevance of a number of functional diversity indices that have a behavior compatible with the proposed partial ordering. © 2011 Elsevier Inc.