What groups according to the external structure are lichen thalli divided into?

The body of a lichen is made up of representatives of two different kingdoms: plants and fungi. Plants are unicellular green algae, which, in the process of photosynthesis, form organic matter and supply them to fungi. And those, in turn, provide the algae with water. The body of a lichen is called a thallus, since there are no tissues in it. By the type of thallus, lichens are:
– bushy – grow on the soil – lichen;
– leafy – attached to tree trunks – parmelia;
– scale – cover the surface of stones – lecanor.