The evolutionary history of leafy liverworts: an approach using the fossil record from worldwide amber deposits

Leafy liverworts (Marchantiophyta: Jungermanniidae) are important components of extant ecosystems, for example in peatlands of the northern hemisphere and in tropical forests where they constitute a large part of the epiphytic biomass. While the early evolution of this diverse lineage remains obscured by its sparse Paleozoic and early Mesozoic fossil record, amber inclusions found since the mid-Cretaceous have provided significant insights into its diversification. To date, ten amber deposits have yielded leafy liverwort inclusions, with the most diverse floras preserved in Cenozoic deposits. Amber fossils have been described from the mid-Cretaceous of Myanmar (Kachin) and Alaska, the Paleogene of India (Cambay), the Baltic region, Germany (Bitterfeld), and Ukraine (Rovno) as well as the Miocene of Ethiopia, China (Zhangpu), the Dominican Republic, and Mexico (Chiapas). The life-like, three-dimensionally preserved amber fossils reveal minute morphological details critical for identifying leafy liverworts and therefore allow for a reliable classification. The fossil evidence also provides age constraints for molecular phylogenies of extant taxa. The resulting divergence time estimates and diversification analyses indicate that — while many lineages probably predate the Permian-Triassic boundary — most extant genera originated during the Cretaceous or Cenozoic, coinciding with the rise of angiosperms. The profound changes of terrestrial ecosystems during the Angiosperm-Terrestrial-Revolution seem to have largely affected the epiphytes which exhibit a steep increase in lineage diversification, while generalists or largely terrestrial taxa were not affected.