Lichens maybe used in several different ways. Added to your trunks or armatures, they make great foliage for deciduous trees. Alone they lend themselves well to representing bushes or hedges. Snip them into small pieces and they represent vegetables in a garden. Pulled apart and greatly thinned out, lichen can be used as ivy growing up the side of a building. Another way to use lichen is to spray it with TSA and sprinkle red, orange, yellow, pink, blue, or any other color over the top of them to make simple flowering bushes.
Keep the lichen tightly sealed in the resealable bag, however, if it dries out, simply add water and it will spring back to life!