Xanthoria parientina in one of the most familiar lichen to be found in Dorset. Indeed, it is one of the most common species across lowland Britain as it, unlike many lichens, it is quite tollerant of air polution and can can often be found in city parks and graveyards.
This particular species falls in to the 'foliose' category meaning the lichen structure is leafy, albeit very small leaves! It grows outwards from the initial starting point and so, on flat surfaces like stone it tends to form a circular shape and as it expands outwards the centre often dies off and peels away. In open situations with plenty of light it can be very orange in colour being much paler in shady conditions.
Xanthoria parientina can be found on almost any substrate (surface) and is very common on trees, rocks and walls. From my observations on nature reserves in Dorset I would say it is most obvious on hedgerow shrubs like hawthorn and blackthorn and is most visible in winter when there are no leaves on these shrubs. Near the sea or where there are rocky outcrops I like to look for it on the tops of large stones where birds perch frequently as it grows readily on accumulated bird droppings!