A method is introduced to compare results of a clustering technique at different levels of abstraction, or of different clustering techniques. The method emphasizes within cluster homogeneity as well as discontinuities between clusters. It has been derived from Hogeweg's method with some important changes. First each cluster is handled separately to determine the ratio between homogeneity and similarity to the nearest neighbour cluster. For a given clustering a weighted average value is computed over all clusters. This average value is standardized using an expected average value for a cluster configuration with the same number of clusters having the same sizes. A low level of the ratio between expected and observed values is supposed to indicate an optimal clustering. A derivation of the criterion is given and results from three sets of data with different properties are evaluated. * Nomenclature follows Flora Europaea for species in Table 2, M ueller-Dombois & Ellenberg (1974) for species in Table 3 and Henkels-van Ooststroom, Flora van Nederland, 19e dr, 1977 for species in Table 4. ** Literature research Mucina & Popma. Methods van Tongeren & Popma. interpretation of results van der Maarel, Popma, van Tongeren and Mucina. *** Recipient of the Research Fellowship in Biology 1980/1981 at the University of Nijmegen.