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The Seashore

Tar Lichens (Verrucaria spp)

Dale Fort headland

Dale Fort headland: note the dark smudge along the splash zone. This is the black tar lichen.

Tar lichens get their common name from the fact that they form great swathes of dark smudges on rocks, giving the rock an impression of being covered in crude oil from an oil spill.

Black Tar LichenBlack Tar Lichen (Verrucaria maura). Note the grazing rough periwinkles. The orange is the lower limit of the lichen, Caloplaca.

The black tar lichen ingrains itself into the rock, covering the bare rock. It is very widely distributed in northern Europe and very common, found on just about all rocky shores but especially more exposed shores where it can cover huge areas. It marks the edge of the littoral fringe and is edible to grazing animals after softening by water. It is believed to be a   terrestrial species capable of tolerating brief periods of saltwater cover.

Green Tar LichenGreen Tar Lichen (Verrucaria mucosa)

The green tar lichen is also abundant but does not form such a distinct band as the black species. In bright sunlight it has a greenish appearance but is not always so distinct. It is found lower down the shore, stretching to the middle shore. If it does not look green you may see that it has a slight shine about it while the black tar lichen higher up the shore is more matt black.

These are not the only tar lichens present on the shore and they are difficult to distinguish from each other. Check out specialist works for more on these other varieties, e.g. Lichens by Oliver Gilbert, (2000) New Naturalist series (HarperCollins)

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