File:A lichen - Parmelia ernstiae - geograph.org.uk - 1213636.jpg

English: A lichen - Parmelia ernstiae. In most respects, this lichen resembles 1184056, but is rarer; like P. saxatilis, it has a network of pale lines on its lobes, and isidia (see the item just cited) are present. However, the centre of this lichen is densely covered in small lobules, a distinctive feature of this species. The tree on which this lichen is growing supported a much richer flora than its near neighbour. In a given area, the number of lichen species found on a tree depends to a large extent on the texture of its bark; most species are better able to establish themselves on rough bark (although there are a few species that favour a smooth surface). Another important factor is the pH of the bark, which can vary greatly between different tree species.