English: A lichen - Peltigera membranacea. The orange-brown discs are the spore-producing structures (apothecia). The pale underside of the lichen was covered in a prominent pattern of raised white veins. Pale rhizines (root-like structures) can also be seen projecting from the underside.

This lichen was growing on the moss-covered base of a tree, just inside the woods. Its upper surface is "bullate" (i.e., covered in blister-like bumps that correspond to the pattern of veins underneath); contrast the smooth upper surface of another very common lichen of this genus: 936434.

Another species, P. canina, is somewhat similar, but is "much rarer than P. membranacea and found mainly on rather basic impoverished dunes and sandy soils" [F.S.Dobson, "Lichens – An Illustrated Guide to the British and Irish Species"].

P. membranacea and P. hymenina are among the fewer than 10% of lichens that contain cyanobacteria rather than algae; they both contain Nostoc, the most common cyanobacterial genus occurring in lichens.

Nostoc is also found as a free-living organism, occurring as gelatinous sheets, or in other forms; see 1470400.