ABSTRACT Aim The current distribution of biodiversity is profoundly shaped by evolutionary history. A prevalent pattern of tropical niche conservatism—most lineages originated in warm and humid tropical climates and have conserved those ancestral traits, making their species difficult to adapt to colder and drier temperate climates—has been identified across many major animal and plant groups, offering explanations for global patterns of species richness and phylogenetic structure (including phylogenetic diversity and phylogenetic dispersion). In contrast, based on regional studies, liverworts have been suggested to exhibit a pattern of temperate niche conservatism, but this hypothesis has not been tested globally. Here, we perform a comprehensive global analysis to test this hypothesis. Location Global. Taxon Liverworts. Methods For liverworts in 390 operational geographic units across the world, phylogenetic diversity was measured as mean pairwise distance and phylogenetic dispersion was measured as the standardised effect size of mean pairwise distance. They were related to six variables representing current climatic conditions. Results We reveal that liverwort phylogenetic diversity is highest in temperate regions with mean annual temperatures approximately ranging from 10°C to 20°C, which holds true across continents and hemispheres. An ancestral state reconstruction recovered a cool ancestral temperature niche for liverworts, estimated at around 13°C. Moreover, while annual precipitation is associated with liverwort phylogenetic diversity more strongly than mean annual temperature, when climatic variables reflecting average, extreme, and seasonality are simultaneously considered, temperature‐related variables emerged as a more significant predictor of liverwort phylogenetic diversity than precipitation‐related variables. Our findings support that liverworts, and by extension to bryophytes, originated under cool and humid climatic conditions. Main Conclusions We propose that the divergence between bryophytes and tracheophytes was driven by adaptations to distinct climatic environments—tropical for tracheophytes and temperate for bryophytes. The simplified morphology and poikilohydric physiology of bryophytes likely evolved as adaptations to cooler, wetter conditions where water stress is less pronounced than in hot climates.
Qian et al. (Sun,) studied this question.