EEL-Understanding the evolution of derived epiphytic liverworts (Lejeuneeae clade, Porellales)

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The subcosmopolitan Lejeuneaceae are the largest family of liverworts, but their taxonomy and diversity is unevenly understood among the different main clades. Lejeuneaceae are especially abundant in the humid tropics, where they make up an important component of the epiphytic, especially epiphyllous, diversity, with most epiphylls nesting in the tribe Lejeuneeae. Earlier reconstructions of diversification patterns in Lejeuneaceae pointed to a constant accumulation of diversity throughout the Cenozoic. However, these divergence time estimates were based on sparse sampling and were likely biased by oversampling of deep nodes.This project aims at generating a plastid and nuclear DNA sequence based phylogeny of Lejeuneeae with an increased sampling including at least 60% of the known species diversity. Particular attention will be given to a balanced taxonomic and geographic sampling, based on newly generated sequences and published data, allowing for further improvements of the current classification. The obtained dataset will be used to generate a dated tree based on DNA sequence variation with integrated constraints derived from the extensive fossil record of Lejeuneaceae. To explore the robustness of the divergence time estimates, average substitution rates from the literature will be employed to calibrate the molecular clock and to explore the impact of fossil constraints on the reconstructions. The dated tree will be used to explore the biogeography of major clades with focus on the processes shaping the extant distribution including the impact of Cenozoic climate changes on the distribution and diversification of Lejeuneeae. Special attention will be given to the timing of the evolution of epiphylls and more generalistic epiphytes, growing preferably on bark rather than on living leaves of vascular plants. Epiphylls exploit an ephemeral habitat (living leaves of euphyllophytes in angiosperm dominated moist forests) that is rather young in an evolutionary context, whereas the accumulation of epiphytic diversity on bark is limited by the competition with taxa occupying these habitats already. The evolutionary age and the short-lived nature of epiphyllic habitats may suggest a higher diversification rate in Lejeuneaceae growing preferably on living leaves compared to their relatives growing preferably on bark (= generalistic epiphytes).