Cryptogams represent diverse photosynthetic organismal groups that are not flowering (i.e., algae, lichens, and bryophytes), usually forming complex but often inconspicuous communities together with cyanobacteria, other hetero- or autotrophic bacteria, microfungi, and archaea.
Due to their poikilohydric lifestyle and lack of stabilizing tissue, cryptogamic/microbial communities are outcompeted by vascular plants in temperate climates and are thus mainly restricted to extreme habitats where vascular plant growth is limited. They colonize a broad range of niches, including the uppermost millimeters of soil (epi- and endogaeic), tree barks and leaves (epiphytic and epiphyllic), and rock surfaces and interiors (epi- and endolithic), as well as artificial substrates such as concrete, glass, or tar. In temperate regions, such communities thrive in shaded forest understories, dry microsites such as path edges, and nutrient-poor grasslands. In hot and cold drylands, their occurrence is largely confined to the open and not vegetated soil surface, where they form biological soil crusts (biocrusts). Biocrusts are estimated to cover ~30% of warm and hot drylands, while their extent in cold deserts remains less well quantified.
These communities are key components of ecosystems, but the magnitude of their contribution to numerous processes is still uncertain (biogeochemical and water cycling, atmospheric processes, biodiversity, etc.). In this session, we ask for contributions on the biodiversity and functional roles of cryptogams from local to global processes such as nutrient and water cycling, trace gas exchange with the atmosphere, soil erosion, mineral weathering, and vascular plant interactions. Studies of their responses to global change as well as other potential threats are also welcomed.