Undersides of Punctelia borreri (left) and Punctelia subrudedcta (right) thalli.

The former was growing on a dead tree and you can see some of the wood as well as part of the black thallus underside. The latter was growing on a boulder. As well as part of the pale thallus underside you can see some of the debris trapped between the thallus and the boulder.

Photographer: Heino Lepp