The species diversity of the family Umbilicariaceae on the equatorial high mountains of South America and Africa is comparatively low. The northern hemisphere at intermediate latitudes has by far the greatest number of species. Around the Equator there is a marked reduction in the diversity. At intermediate southern latitudes it rises slightly again and then falls towards the continental Antarctic. These diversity gradients mainly seem to reflect the latitudinal differences in area of dry land and mountains, thus a rough species-area relationship. The equatorial and Antarctic species mainly reproduce asexually by thalloconidia, and the adaptive significance of this type of reproduction in extreme habitats is discussed. high altitudes, tropics, biodiversity, reproduction, Umbilicariaceae. This paper is dedicated to professor Hildur Krog, explorer and connoisseur of the lichen flora of African mountains, on her 75 th birthday in 1997. It is also dedicated to the memory of Josef Poelt who in his treatment of the Himalayan members of the genus Umbilicaria called these lichens ‘the high mountain lichens of the world par excellence’ (die Hochgebirgsflechten der Erde par excellance)