Definitions of biogeographical regions in Switzerland are traditionall
y based on expert knowledge. Six different sets of systematically coll
ected floristic data, including 129 to 2280 species, were analysed by
means of minimum variance analysis, using two similarity measures, the
correlation coefficient of standardized data and the Jaccard coeffici
ent. The resulting groupings are compared with some of the traditional
classifications using kappa statistics. The main divisions obtained b
y the statistical procedure are roughly corresponding to those based o
n expert knowledge. There is evidence that standardized and correlated
distribution data tend to build more coherent groups. Datasets with a
high number of species are divided into more coherent groups than dat
asets with a low number of species. Biogeographical divisions of Switz
erland into 5, 11, 19 and 30 groups are suggested. Possible causes for
these patterns are discussed.