Lichens

Lichen growing on a tree trunk. The Blue Mountains, Australia.

A lichen is not a single organism. It is actually symbiosis between different organisms - a fungus and either an alga or cyanobacterium. 
For an excellent explanation on lichens, click  here  to go to this website: https://www.anbg.gov.au/lichen/what-is-lichen.html

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Lichen growing in Victoria, Australia

Lichen growing on a tree trunk. The Blue Mountains, Australia.

Lichen's growing in Victoria, Australia

Lichen's growing in Victoria, Australia

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Lichen's growing in Victoria, Australia