The diversity of bryophytes on the different islands of the Azores varies much between 104 and 324 species. Attempts have been made to explain the heterogenity of the bryoflora. There is a correlation between species numbers and age of the islands in the way that the youngest islands (Pico) has the lowest species numbers in spite of the fact that it is the highest island. The species numbers of the other islands are correlated with the maximum elevation and with the size of the islands. The liverwort-moss ratio varies between 1.21 and 1.67 and shows a distinct humidity gradient between the islands. The floristic affinities between the islands are calculated by a cluster analysis. They show no correlation with the location of the islands (nearest neighbour), size, age, elevation or species numbers, which indicates that the species composition is mainly determined by chance. Ten species (2,3%) are endemic to the Azores and 14 species (including one genus) are endemic to the Macaronesian Islands. Some of the endemics are questionable, others may occur elsewhere in the tropics under a different name, but there is fossil prove that the others are relicts from the Tertiary which survived extinction during Quaternary in Europe
