There is an affinity between rocks, lichens and sea sedum, as shown in these photos. The maritime climate is just right for them all. Sea sedum keeps to a low height, absorbing moisture in thick fleshy leaves, establishing itself on hard coastal grassy ground and in rocky crevices where moisture is held.
Lichens are ‘dual’ organisms. They consist of two (or more) different life-forms living together symbiotically in a more-or-less well defined body or thallus. info
The main partner is the fungus or mycobiont. The other partner is a green alga or a cyanobacterium (the photobiont). Many cyanobacteria are able to fix nitrogen which is an essential nutrient. In 10% of lichens (e.g. Collema and Leptogium) the photobiont is a cyanobacterium. The nutritional benefits of having a nitrogen fixing capability is why some lichens, where the primary photobiont is a green alga, have evolved separate structures called cephalodia which contain cyanobacteria (the secondary photobiont). So for these lichens there are three partners in the symbiosis.
Lichens are named after the fungal partner.
Lichen – White: Crustose lichen. Lecanora rupicola (british lichens.) good photo on lastdragon.org (Rimose type; thallus is initially continuous but becomes cracked into irregularly-shaped and sized pieces).
Sea Ivory – Ramalina Cuspidata (west coast) or Diploschistes caesioplumbeus
Lichen – Pale Green: Sea Ivy – (family Ramalinaceae) : Ramalina siliquosa similar to lichen found in Exmoor rain forests.
Lichen – Black: Tar Lichen, shiny surface Verrucaria maura …’forms a thin, matt-black layer on rock surfaces that can resemble an oil stain. Reproductive bodies may be present as tiny black spots. Under magnification the surface is seen to be covered with a mesh of fine cracks that resemble dried mud’.
( or Plcynthium nigrum (rougher surface)
Photographs available in higher resolution.