 Many ascomycetes also form symbiotic relationships with other organisms, including plants and animals.Probably since early in their evolutionary history, the Ascomycota have formed symbiotic associations with green algae ("Chlorophyta"), and other types of algae and cyanobacteria.These mutualistic associations are commonly known as lichens, and can grow and persist in terrestrial regions of the earth that are inhospitable to other organisms and characterized by extremes in temperature and humidity, including the Arctic, the Antarctic, deserts, and mountaintops.