Orange-fruited elm-lichen  (Caloplaca luteoalba)

This species occurs only in the east of England and Scotland although it was once much more widespread. Its range covers western Europe, but it has declined rapidly with the advent of Dutch Elm disease, which has killed almost all of the mature elms in the UK on which it grows. The lichen now appears to be extinct in Denmark, the Netherlands and northern Germany. It has also been recorded in North America. It is now only known in England from three trees in Norfolk, Suffolk and Oxfordshire where it grows on either black poplar or horse chestnut, all in open situations. It still occurs on elm in eastern Scotland where Dutch elm disease has not yet reached. In addition, it is known from chalk pebbles on one or two sites in the Chilterns and South Downs.

As its name suggests, this lichen is associated with elm trees, where it grows on the bark. It has also been recorded on black poplar Populus nigra ssp betulifolia, horse chestnut Aesculus hippocastanum, sycamore Acer pseudoplatanus and field maple A. campestre. It is also occasionally found on chalk pebbles in downland.