There is a great deal of exposed rock in Arches, and much of it is spotted with multicolored lichens. Lichens usually grow on north-facing surfaces since reduced solar radiation is an advantage for many organisms in the desert. Lichens also colonize healthy, mature biological soil crust, and occasionally on live or dead plant material. Many species of lichen are found in Arches.
A lichen is actually a simple community of at least two organisms: fungi combined with green algae or cyanobacteria, or sometimes with both. The lichen structure is more elaborate and durable than either fungi or algae alone. Green algae and cyanobacteria manufacture food via photosynthesis, while fungi provide a buffer against weather and are capable of extracting nutrients from soil and rock.
Lichens are well adapted to arid climates. They can carry on food production at any temperature above 32º Fahrenheit. Lichens can absorb more than their own weight of water, and can absorb temporary water like dew almost directly into their algal cells (the water does not need to go through roots and stems as it does in vascular plants).
Many plants benefit from the presence of lichens. The cyanobacterial component of lichens can transform atmospheric nitrogen (unusable to most organisms) into a form that is an essential nutrient for life. This is especially important in desert ecosystems, where lack of nitrogen is known to limit productivity.