Those lichens which are intimately attached to the habitat and form a thin, flat and hard covering are called crustose lichens. They are also called lichens. Like- Graphis scripta, Lecanara muralis, Strigula angulul, Cryptothecia rubrocinta, Diploicia canescens, Calicium indicum, Pyrenula micheneri, Arthonia radiata, Trypethelium virens, Xylographa vitiligo etc.