(1762) Ramalina siliquosa, also known as sea ivory,[2] is a tufted and branched lichen which is widely found on siliceous rocks and stone walls on coastlands round the British Isles, occasionally slightly inland.

[6] Ramalina siliquosa is part of a complex of closely related lichen species that grow on maritime cliffs in Europe and East Asia.

Molecular phylogenetics analysis has revealed that this complex comprises three distinct evolutionary lineages:[7] The European species R. siliquosa and R. cuspidata show distinct zonation patterns on cliffs, with different chemotypes occupying different vertical zones.

[7] Contrary to previous hypotheses, R. siliquosa and R. cuspidata are not closely related "sibling species", but represent separate evolutionary lineages.

The chemical variation and zonation patterns in this complex appear to be a result of parallel or convergent evolution rather than recent speciation.