Lichen attach to rocks via a central holdfast (umbilicus).
“The umbilicus is of vital importance for the Umbilicaria species, since it fastens the thallus to the rock.” (Gauslaa 1984:20)
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Attach Permanently
A living system can conserve energy by attaching permanently to a particular site because it can take advantage of resources that come its way, rather than expending energy to move to resources. A permanent attachment, intended to last the lifetime of the living system, creates special challenges. For example, physical mechanisms, such as the anchor that holds a marine algae to the ocean’s bottom, must be able to withstand forces that can pull it off its substrate. Chemical mechanisms, such as a barnacle’s glue, must avoid both physical and chemical breakdown, such as being dissolved by water.
Lichens
Lichen (“to lick”): Iceland moss, reindeer lichen, rock tripe
Lichen are composed of two organisms: algae (or cyanobacteria) and fungi. In this symbiotic, or beneficial relationship, algae produce simple sugars through photosynthesis which are consumed by fungi, and fungi provide algae with water and shade. Sometimes referred to as “moss”, lichen superficially resemble, but are not true moss. It is estimated that lichen cover 8% of the Earth’s land surface. From the subzero temperatures of the Arctic to sweltering deserts, lichen can be found on flat surfaces; gravestones, city buildings, rocks, trees, soil, and other flat surfaces. While some lichen have a cracked, crusty appearance, others are more foliose, or leaf-like in appearance. Lichen are currently being used as an inexpensive way to assess air quality, as some are sensitive to pollution and metal contamination. In the Arctic, caribou depend on reindeer lichen (Cladonia spp.) as their main source of food during migration.
