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In nature, lichen are composite organisms consisting of fungi and photosynthetic bacteria or algae (a type of symbiont called a photobiont) living in a symbiotic relationship.  Lichens are named based on the type of fungal component they contain. 

There over 20,000 known species  and over 3,000 are known in Australia. 

Lichen take on a variety of biochemistries and form quite differently due to their individual fungal or bacterial components. 

Lichen are well known for growing on rock surfaces, most likely a Xanthoparmelia species  . image: R.Conan-Davies

Close-up image of a lichen, click image for fullsized image. image: R.Conan-Davies

Orange coloured lichen fro the Swiss Alps. The colour may help absorb different wavelengths of light. image: R.Conan-Davies

There are different types of lichen:

Fruticose lichens  

These stand erect or pendulous and are three-dimensional.

An example of a fruticose lichen from the Swiss Alps. image: R.Conan-Davies

Crustose lichens 

These are essentially two dimensional and firmly attached to the surface they live on. It's basically impossible to view the underside of these lichen.

Foliose lichens

These are  halfway between crustose and fruticose. But essentially flat though they do have some obvious three dimensional aspects to them.


Lichens are often studied as bioindicators because they absorb a wide range of chemicals that may be present in the atmosphere. 

References/further reading:

      What is a lichen: Australian National Botanical Gardens

     Lichens as Bioindicators US National Parks Service

     Air pollution and its effects on lichens, bryophytes, and lichen-feeding Lepidoptera: review and evidence from biological records - Oxford University Press