Article

The similarity index suggested by Paul Jaccard 120 years ago has been one of the best-known coefficients in statistical ecology and other research fields in which the objects to be compared are described in terms of the presence or absence of many characters. Jaccard and his immediate followers used the coefficient for the comparison of floras of different localities and phytosociological relevés, based on the list of constituting species. A historical and mathematical overview reveals that, in addition to applications in ordinations and classifications, partitioning the coefficient into additive fractions opens unlimited opportunities for evaluating taxonomic, phylogenetic and functional diversity and related phenomena of ecological communities.