Leprose lichen

A leprose lichen is a lichen with a powdery or granular surface.[1] Leprose lichens lack an outer "skin," or cortex.[1] If a crustose lichen starts to disintegrate, it will appear powdery, but crustose lichens will leave a cortex surface, and leprose lichens do not.[1][2] 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.

Acacia bark covered in green Leprose lichen.