Adaptation and interaction of saxicolous crustose lichens with metals

One of the most successful mechanisms enabling fungi to survive in extreme subaerial environments is by formation of mutualistic symbioses with algae and/or cyanobacteria as lichens. Collections, field and mineral weathering studies and developments in modern instrumental and analytical techniques have considerably advanced knowledge in understanding tolerance mechanisms to stress, environmental adaptation, species concepts and evolutionary processes in lichens colonising metalliferous habitats. This review focuses on the predominantly saxicolous, crustose, taxonomically notoriously challenging Acarospora sens. lat. Pioneering studies investigating element and substance localization in Acarospora sens. lat. in different geological terrains led to the discovery of novel fixation mechanisms, new minerals and substances associated with lichens, and new taxa and evolutionary lineages. Acarospora sens. lat. are generally under-represented in collections. Systematic sampling of Acarospora sens. lat. and other saxicolous lichens, in different mineralogical environments is now required, a priority being those occurring in extreme habitats at risk from climatic and other environmental changes. The potential for the discovery of new lichen and mineral species associated with Acarospora and other saxicolous crustose lichens, is high. These may represent special mechanisms to tolerate metal toxicity and other forms of environmental stress, including photoprotection.