Lichen

Two lichens on competing for space on the branch of a young tree.  The brown and white one is probably Lecanora chlarotera; I am not sure of the identity of the black and grey one [Note added 2011-03-31: it is possibly Lecidella elaeochroma.].  According to The Observer's Book of Lichens (Kenneth L. Alvin, 1977), L. chlarotera is similar to L. campestris but the former grows on trees while the latter grows on calcareous walls and rocks.

Photo taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2011-03-26.