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250 words max.) 1 Besides their alleged therapeutic effects, mistletoes of the genus Viscum L. 2 (Viscaceae) are keystone species in many ecosystems across Europe, Africa, Asia and 3 Australia because of their complex faunal interactions. We here reconstructed the 4 evolutionary history of Viscum based on plastid and nuclear DNA sequence data. We obtained 5 a highly resolved phylogenetic tree with ten well-supported clades, which we used to 6 understand the spatio-temporal evolution of these aerial parasites and evaluate the 7 contribution of reproductive switches and shifts in host ranges to their distribution and 8 diversification. The genus Viscum originated in the early Eocene in Africa and appeared to 9 have diversified mainly through geographic isolation, in several cases apparently coinciding 10 with shifts in host preferences. During its evolution, switches in the reproductive mode from 11 ancestral dioecy to monoecy imply an important role in the long-distance dispersal of the 12 parasites from Africa to continental Asia and Australia. We also observed multiple cases of 13 photosynthetic surface reduction (evolution of scale leaves) within the genus, probably 14 indicative of increasing specialization associated with the parasitic lifestyle. Even compared 15 with other parasitic angiosperms, where more host generalists than specialists exist, Viscum 16 species are characterized by extraordinarily broad host ranges. Specialization on only a few 17 hosts from a single family or order occurs rarely and is restricted mostly to very recently 18 evolved lineages. The latter mostly derive from or are closely related to generalist parasites, 19 implying that niche shifting to a new host represents an at least temporary evolutionary 20 advantage in Viscum. 21 22 Keywords 23 mistletoes; parasitic plants; host range evolution; geographic range expansion; reproductive 24 switches; Viscum 25 3

We studied the influence of regional and local variables on the liverwort diversity within natural forest vegetation of Uganda to contribute to our understanding of the mechanisms and processes determining species richness. To this end, we compared the species richness distribution patterns of epiphytic and non-epiphytic liverworts (Marchantiophytina) in 24 plots in the forests of four Ugandan national parks. We recorded a total of 119 species and subspecies from 18 families, including 16 new species records for the country. We used generalized linear models (GLMs) and the relative variable importance of regional and local climatic and environmental variables to assess their respective impact on the species diversity. We found that the richness patterns of total and epiphytic richness were largely driven by regional climatic factors related to temperature and water-availability. In contrast, species diversity of non-epiphytic and rare species was additionally strongly determined by local-scale microhabitat factors such as height of forest canopy and slope inclination, reflecting the availability of suitable microhabitats. We conclude that macroclimatic variables perform well in predicting epiphytic liverwort richness, whereas the adequate prediction of nonepiphytic richness requires site-specific variables. Also, we propose that richness of epiphytic liverworts will be impacted more directly by climate change than richness of non-epiphytic and rare species.

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The study of elevational gradients allows to draw conclusions on the factors and mechanisms determining patterns in species richness distribution. Several earlier studies investigated liverwort diversity on single or few elevational transects. However, a comprehensive survey of the elevational distribution patterns of liverwort richness and their underlying factors is lacking so far. This study's purpose was to fill this gap by compiling an extensive data set of liverwort elevational patterns encompassing a broad diversity of mountains and mountain ranges around the world. Using polynomial regression analyses, we found a prevalence of hump-shaped richness patterns (19 of 25 gradients), where liverwort species richness peaked at mid-elevation and decreased towards both ends of the gradient. Against our expectation and unlike in other plant groups, in liverworts, this pattern also applies to elevational gradients at mid-latitudes in temperate climates. Indeed, relative elevation, calculated as the percentage of the elevational range potentially inhabited by liverworts, was the most powerful predictor for the distribution of liverwort species richness. We conclude from these results that the admixture of low-and high-elevation liverwort floras, in combination with steep ecological gradients, leads to a mid-elevation floristic turnover shaping elevational patterns of liverwort diversity. Our analyses further detected significant effects of climatic variables (temperature of the warmest month, potential evapotranspiration, and precipitation of the warmest month) in explaining elevational liverwort richness patterns. This indicates that montane liverwort diversity is restricted by high temperatures and subsequent low water availability especially towards lower elevations, which presumably will lead to serious effects by temperature shifts associated with global warming.