Article

This study aims to analyse the role played by some physiographic and ecologic variables such as area, isolation, altitude and substratum type on the bryophyte species richness of 49 small ltalian islands. Both floristic similarity between islands and bryophyte species richness depend above ali on the island size. The other variables, i.e. the prox imity to the c10sest continent or major island, the distance between islands and the type of substratum, account for only small differences between the island bryofloras. Unexpectedly, the number of bryophyte species in these islands is not negatively related to the distance fTom the continent. This outcome is due to the confounding effect of island size and age, as well as to the stronger human impact that is likely to occur in close-to-eontinent islands. The high slope of the speeies-area curve indieates a very scarce bryophyte immigration, even trom the closest islands. The low dispersion ability is partly related to some life history traits of the xerophilous mosses. The only two endemi e species (Rhynchoslegium strongylense and Thamnobryum cossyrense) that oeeur in no more than five islands were not suffiei ent to test whether the isolati on from the eontinent has favoured the differentiation of new species. The outeome of the analyses performed refleets the current bryo-chorological knowledge coneerning the small Italian islands, and thus it is likely that reports of new species could change some bryogeographie patterns revealed in this study.