Leprose lichen

A leprose lichen is a lichen with a powdery or granular surface. Leprose lichens lack an outer "skin," or cortex. If a crustose lichen starts to disintegrate, it will appear powdery, but crustose lichens have a cortex, and leprose lichens do not. Leprose lichens have no inner or outer cortex. They sometimes have a weak kind of medulla, but are composed mainly of the fungal hyphae and an algae.