Geographic and ecological effects on species richness of liverworts worldwide

Liverworts are one of the oldest lineages of the extant land plants but the geographic patterns and ecological determinants of their species richness have not yet been studied at a global scale until now. Here, using a comprehensive global database, we find that regional species richness of liverworts in general 1) shows a clear latitudinal diversity pattern, 2) is highest in mountains, presumably reflecting the effects of habitat heterogeneity and the occurrence of cloud forest, 3) is more strongly influenced by contemporary climate than by climate change during the Quaternary, 4) is more strongly affected by precipitation-related than by temperature-related variables, reflecting the poikilohydric nature of liverworts and hence their water-dependence, and 5) is more strongly affected by climate extremes than by climate seasonality. However, we find regional deviations from these general patterns, especially in the Southern Hemisphere where the distinct arrangement of land masses leads to different climatic patterns and thus climate-species richness relationships. Compared with other major land plant lineages, liverworts show the same importance of precipitation-related factors as ferns, whereas in angiosperms temperature also plays an important role, reflecting the different physiological adaptations of these groups to drought and cold stress, and providing insights into the different evolutionary pathways taken by these lineages.