A lichen is a composite organism that emerges from algae or cyanobacteria (or both) living among filaments of a fungus in a mutually beneficial relationship. Lichens come in many colours, sizes, and forms. The properties are sometimes plant-like, but lichens are not plants. Lichens may grow like a tiny, leafless, branching shrub, like it has leaves, like a crust of paint on a surface or have other growth forms. Common names for lichen may contain the word “moss” and lichens may superficially look like and grow with mosses, but they are not related to mosses or any plant. Lichens do not have roots that absorb water and nutrients like in plants – instead they produce their own food from sunlight, air, water, and minerals in their environment. They are not parasites on the plants they may grow on, but only use them as a substrate to grow on or in. Lichens occur in a very wide range of environmental conditions, and can grow on almost any surface. Lichens are abundant growing on bark, leaves, mosses, on other lichens and hanging from branches “living on thin air”. They grow on bare rock, walls, gravestones, roofs, exposed soil surfaces, and in the soil as part of a biological soil crust. They can survive in some of the most extreme environments on Earth. They can even live inside solid rock, growing between the grains. Some lichens do not grow on anything, living out their lives blowing about the environment. It is estimated that 6% of Earth’s land surface is covered by lichen. (source Wikipedia).
Here’s a small selection I found growing on the trees nearby.