File:A lichen - Collema furfuraceum - geograph.org.uk - 1054150.jpg

English: A lichen - Collema furfuraceum. Within their outer fungal layer, most lichens contain algae. Those in the genus Collema do not; instead, they contain cyanobacteria of the genus Nostoc. When Nostoc occurs in a lichen, it is usually contained in a thick gelatinous "matrix".

As a consequence, such lichen species are often gelatinous, swelling greatly when wet; others (including the species shown in this photograph) do not swell much. (Nostoc species are sometimes found as free-living organisms; see 1314485.)

Collema furfuraceum is dark green-brown to black, and its lobes have a pattern of radiating ridges, as can be seen in the photograph [see F.S.Dobson, "Lichens - An Illustrated Guide to the British and Irish Species"]. When examined through a hand-lens, these ridges were seen to be bristling with tiny rod-shaped structures (which are called isidia); this is another characteristic of this species. The work cited above mentions that this species is frequent on deciduous trees, or on mosses on trees and rocks (usually coastal).

The specimen shown in the photograph was growing on a rock close to the top of the beach, not far from an overgrown footpath. Several rocks nearby had extensive colonies of this species, mainly growing in ridges and depressions.

For another species that was found on a neighbouring rock, see: 1054164.