A global analysis of mosses reveals low phylogenetic endemism and highlights the importance of long-distance dispersal

Aim: Digitization of herbarium specimens and DNA sequencing efforts in the past decade have enabled integrative analyses of patterns of diversity and endemism in a phylogenetic context. Here, we compare the best available floristic databases to a comprehensive specimen database to examine spatial patterns of moss phylogenetic assembly. We test the hypotheses that 1) mosses exhibit phylogenetic regionalization, 2) islands contain significantly high phylogenetic diversity, and 3) that moss phylogenetic endemism is low on a global scale.

Location: Global

Taxon: Mosses

Methods: We developed a phylogeny of 3,654 moss species using 25 markers and compiled a global specimen database from online repositories. We calculated floristic and phylogenetic measures of diversity and endemism and performed randomizations to test for significant deviations from expectations. We use rarefaction and extrapolation to alleviate substantial differences in sampling effort across the globe. We used both phylogenetic and floristic methods to test for spatial regionalization. We compare our specimen-based results to those obtained using a floristic dataset. 

Results: Phylogenetic diversity is more robust to missing data than species richness. Mean phylogenetic distance was significantly higher than expected in areas with high species richness, indicating that reported richness in these areas is likely a product of repeated colonization. Phylogenetic endemism is low globally. Phylogenetic regionalizations cluster into a Holarctic/Holantarctic temperate region, a pantropical region, and a region composed of Australia, New Zealand, and South Africa.

Main Conclusions: Future efforts for collecting, sequencing, and databasing moss species should focus on the tropics, particularly Africa and Southeast Asia. We provide further evidence to support several important theories developed in moss biogeography, including the role of long-distance dispersal in shaping floristic patterns, the dominance of anagenesis in driving patterns of island diversity, and the role of climatic instability in driving patterns of assembly in the Holarctic.