The diversity and abundance of terrestrial, lithophytic cyanobacteria in tropical biomes and the variety of rock habitats which they occupy are discussed. The following results are presented in detail. Exposed rock surfaces on different continents and under different climatic conditions are occupied by a cosmopolitan, well-adapted, low-diversity microbial community dominated by cyanobacteria and cyanobacterial lichens. For inselbergs (isolated rock outcrops) in dry savanna, the ratio of rock covered by lichens to that covered by free cyanobacteria is approximately 5:3. In humid savannas this ratio is approximately 1:26, and in rainforests there are hardly any lichens on rocks. The primary production of epilithic communities, expressed as CO2 fixed calculated from chlorophyll a, can reach an annual 27 g m−2. When calculated for a hypothetical inselberg, production values for very dry thorn bush savanna, dry savanna and humid savanna are 1:3·2:4·2 on the basis of the entire inselberg, and 1:3·2:1·4 when calculated on a square metre basis (due to a larger area covered but lower productivity in the humid savanna). Biofilm communities are important in biogenic weathering and they enrich the soils surrounding the rocks with nitrogen.