LICHEN BIOLOGY

Read Also

Lichens are composite, symbiotic organisms made up from members of as many as three kingdoms.

The dominant partner is a fungus.  Fungi are incapable of making their own food.  They usually provide for themselves as parasites or decomposers. 

The fungi cultivate partners that manufacture food by photosynthesis.  Sometimes the partners are algae; other times cyanobacteria, formerly called blue-green algae.  Some fungi exploit both at once.  Cyanobacteria can take nitrogen from the air and turn it into biologically usable compounds so lichens with cyanobactetria can make major contributions to soil fertility.

Given appropriate amounts of light and moisture, clean air and freedom from competition, lichens can colonize almost any undisturbed surface.  Most lichens grow very, very slowly, often less than a millimeter per year, and some lichens are thought to be among the oldest living things on Earth.

Lichens produce an arsenal of more than 500 unique biochemical compounds that serve to control light exposure, repel herbivores, kill attacking microbes and discourage competition from plants.  Among these are many pigments and antibiotics that have made lichens very useful to people in traditional societies.

Some lichens make entire non-sexual reproductive packages which are tiny projections from the surface of the lichen that can break off easily and grow into a new lichen.  Most lichens are very brittle when they are dry, and some depend on breakage to produce fragments that can be blown around by wind, washed along by water or carried off as passengers on insects or birds.  Other lichen fungi make spores.  To form a new lichen, these fungal spores need to capture new photosynthetic partners after they germinate.

Individual lichens have been known to live for over 2,000 years.

 Lichens are identified taxonomically as if they were fungi.  Three lichen forms are commonly used in the identification of species:   foliose, fruiticose, and crustose.  Fruiticose lichens have no clearly distinguishable upper and lower surfaces and grow erect.  Foliose lichens have flattened upper and lower surfaces and are leaf-like in appearance.  Crustose lichens form a crust over a surface.

Some lichens can be eaten and many are used in science to benefit humans.  One common and exciting use of lichens is environmental monitoring.  Because lichens grow slowly and absorb their nutrients from the substrate, air and water, they come in contact with many minerals.  If lichens concentrate too many toxic elements like sulfates and other metal compounds, it will kill the photobiont and result in the lichen’s death.  Using lichens to monitor acid rain and air pollution is a relatively new and inexpensive way to monitor air pollution.