Parmotrema perlatum

A relatively large and leafy lichen, often with convoluted lobes with soredia on their edges. It is pearly grey when dry, but greener when damp. If the cortex is scraped, a drop of K on the white medulla will turn yellow-orange (the similar-looking Hypotrachyna go red).

Usually on tree trunks but sometimes on rocks.

All year round.

Widespread, common in much of western and southern Britain; until recently largely absent from central and eastern England as a result of sulphur dioxide pollution, but now rapidly re colonising these areas as levels have dropped.

Probably increasing in Leicestershire and Rutland.