File:A lichen - Trapeliopsis pseudogranulosa - geograph.org.uk - 1045111.jpg

English: A lichen - Trapeliopsis pseudogranulosa This specimen was found growing on a mossy rock in a dry-stone wall; the wall lies between a steeply ascending footpath and the neighbouring field (to the south).

This is a species that is found in damp shaded habitats, often on mosses or on dead or decaying plant material ["Lichens - An Illustrated Guide to the British and Irish Species" by Frank S. Dobson]. That fits the sitation in which this particular specimen was growing: the abundant moss on this rock will retain moisture well, while a clump of trees at the edge of the neighbouring field provides suitable shade. The lichen sometimes appears to be growing directly on rock, but it will usually be found that it is growing on moss that is covering the rock (as is the case here).

The orange and green colour combination of this lichen is quite unusual. (The identity of this species can be confirmed by performing fairly simple chemical tests on small fragments of the lichen; for example, a 10% solution of potassium hydroxide gives a purple reaction with the orange parts, but no reaction with the green parts.)

The same species occurs in North America, where the orange parts of the lichen, abundant here, are relatively infrequent ["Key to the Lichen Genera of the Pacific Northwest" by Bruce McCune].