(RANKIN) of equivocation information (1-:) and interaction information (M). The method is described in the present paper for I: and in a previous paper (Orloci, 1976) for M. The results presented in this paper suggest that for Species Rank order Information Percentage of total* species to be weighted according to their suitability to I· M I M r M characterize isolated groups of releves in a phytosociolo­ 5 7 54.15 2.31 17.97 0.82 gical table, the equivocation information may serve as a 9 5 49.86 23.19 16.55 8.22 3 3 9 47.79 0.56 15.86 0.20 suitable weight. The appropriate formulations are derived 6 4 8 36.18 1.18 12.01 0.42 4 5 3 24.36 59.34 8.09 21.03 and computed for some data from a salt marsh community. 8 6 4 24.25 39.04 8.05 13.84 10 7 I 21.96 71.17 7.29 25.23 7 8 2 18.67 69.01 6.20 24.46 9 10 18.40 6.11 10 6 5.64 16.31 1.87 5.78 References Total 301.00* 282.11 * 100.00 100.00 Feoli, E. 1973. An index for weighing characters in monothetic classifications. (Italian with English summary). Giorn. Bot. Ita!' 107: 263-268. Gower, J.e. 1967. A comparison of some methods of cluster is a monotone, increasing function of sample size if .. ).