Peltigera spp. – Dog lichen
It will only grow in compacted ground or lawns that have poor drainage and or shady conditions. It will usually make the surface slippery. A lot of the time it will grow around or under trees and shrubs.
It can be identified as a greyish-black scale called a thallus and is often encountered growing on the lawn. The thallus is papery in dry conditions and plumps up when wet. The lower surface has white root-like structures called rhizines.
An interesting fact – The common name arose because of the shape of the fruiting bodies which resemble a dog’s teeth.
There will usually be moss present in the lawn along with the lichen, scarification will help remove the fungus and the moss, however it is just as important to fix the underlying cause – compaction
The lawn will require aeration if it is particularly bad the lawn may also required additional drainage or a topdressing with a free draining sand or soil into the holes after aeration.
For particularly poor lawns with heavy moss and lichen, overseeding may be required.