Crustose Lichens Crustose lichens, as their name implies, form a crust on the surface of the substrate on which they are growing. This crust can be quite thick and granular or actually embedded within the substrate. In this latter case the fruiting bodies still rise above the surface. In many crustose lichens the surface of the thallus breaks up into a cellular, crazy-paving like pattern. Crustose lichens tend to grow out from their edges and have their fruiting bodies in their centre.
Crustose lichens are very difficult to remove from their substrates.
Squamulose lichens Some lichens have a portion of their thallus lifted off the substrate to form 'squamules'. They are otherwise similar to crustose lichens in that they possess an upper cortex but no lower cortex. These have an upper and lower cortex. They are easier to remove from their substrate when collecting because of this. Lichens Fruticose lichens are shrubby lichens.