| Summary: | Based on extensive new collections, a key to and a list of 11 species of the lichen genus Umbilicaria in Bolivia are provided, and their diversity, altitudinal distribution, biogeographical affinity and reproductive strategies are discussed. Umbilicaria africana, U. aprina, U. cinereorufescens, U. decussata, U. dendrophora, U. leprosa and U. vellea are reported from Bolivia for the first time. The Umbilicaria species of Bolivia belong to several biogeographical elements: an “international” high altitude group of species (4000–5500 m) found in most alpine or Arctic areas of the world (U. aprina, U. cinereorufescens, U. decussata, U. dendrophora, U. nylanderiana, U. vellea), and a central Andean endemic element (U. calvescens, U. leprosa, U. haplocarpa) which completely dominates at lower altitudes (2500–4000 m). In addition the mainly Southern Hemispheric U. africana is abundant in the high alpine areas. A two-phase scenario is suggested where the ancestor of the endemic element colonized and evolved in the Andes while the mountain chain was still fairly low, while the international element is a comparatively recent addition.
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