Athelia arachnoidea

A pathogen of lichens and algae, forming large, whitish rings on tree triunks, etc. where the host lichens has been killed.  At the edges of the ring is a zone of white cobweb-like growth of hyphae. Brown spherical sclerotia may be found on the surface. 

Photograph in its habitat; note habitat and substrate.  A detailed photo of the cobwebby hyphae is helpful.

On rocks and tree trunks where the host lichens are present.

All year round

Widespread and fairly frequent in Britain.

Fairly frequent in Leicestershire and Rutland.