Lichens

I see them all the time living here, prolific particularly on the sandstone walls in this area. These are called Crustose Lichens - like a crust of paint both flat and crusty. A Lichen is a mutual relationship between a fungus and an algae which benefits both - a symbiotic relationship.
Lichens are not plants and do not have roots for absorbing water. They provide their own food from sun, air, water and minerals. They are not a parasite of the plant or other substrate which they are growing on. Crustose Lichens are the slowest growing of all lichens which means a tiny piece of Lichen that you see about a half inch across has taken years and years to grow.
There is a lot of Lichen on the stone walls of this house which I think looks very attractive and wouldn't dream of scrubbing it off. Lichens rule!!!