What are lichens?

1 Answer
May 29, 2018

A lichen is a composite organism that is a result of an algae/cyanobacterium living among the hyphae filaments of two fungi in a mutually beneficial symbiotic relationship.


The fungal component of lichens is called as mycobacterium and the photosynthetic partner in a lichen is called a photobiont.

The combined lichen has properties different from those of its component organisms. Their properties are sometimes plant like and they may superficially look like mosses, but they are not plants or moss.
Lichens do not have roots that absorb water and nutrients as plants do,but like plants they produce their own food by photosynthesis. When they grow on plants, they do not live as parasites, but use the plant as a substrate.

Lichens can be seen as being relatively self-contained miniature ecosystems, where the fungi, algae or cyanobacterium have the potential to engage with other microorganisms in a functioning system. The combination of algae/cyanobacterium with the fungus has a very different morphology, physiology and biochemistry than the component fungus, algal/cynobacterium growing by itself, naturally or in culture.

The algae/cyanobacterium benefit by being protected by the environment by the filaments of the fungi, which also gather moisture and nutrients from the environment, and provide an anchor to it. Algae produce sugars that are absorbed by the fungus by diffusion into haustoria which are in contact with the walls of the algal cells.

It is estimated that 6% of Earth's land surface is covered by lichens and there are about 20,000 known species of lichens.