Lichens

In nature, lichen are a composite organism consisting of fungus and photosynthetic bacteria or algae (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 biochemistry and forms quite differently to their individual fungal or bacterial components. 


P1196497

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


Xanthoparmelia  lichen

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


There are different types of lichen:

Fruticose lichens  
These stand erect or pendulous and are three-dimensional.

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.


Reference: