Nature Notes from Skye
(and occasionally other places)
Sun 6 Mar 2005
The "black zone" on the shore. Round almost the entire coast of Britain, except where there are no rocks, extends this black band several feet wide either side of the high tide mark. It is due to the rock being encrusted by the lichen Verrucaria maura. The bare whitish patches in the left-hand picture are where other lichens have grown over the Verrucaria and then decayed and fallen off. These were mostly Caloplaca species, as far as I could see from their remains, and there is a fine yellow rosette of Caloplaca thallincola visible near the top of the rock. The right-hand picture shows the Verrucaria close to; the surface is divided into small polygons by a network of cracks.
Here is a closer view of the Caloplaca rosette, looking like a primitive rock painting of the sun. I wonder what our ancestors made of this and other shapes assumed by lichens, which seem closer to human art than anything else in nature. Even today they exert a powerful pull on the psyche, and it's easy to imagine shamans using them for divination. The right-hand picture shows a still closer view.
If that was the sun, this is a cloud. It's another lichen growing over the Verrucaria, and appears to be Lecanora dispersa, though I can find no mention of this growing in a maritime habitat or on non-alkaline rocks.
Further down the shore, the black Verrucaria maura is replaced by the green Verrucaria mucosa. It does not form such a continuous band as V maura, but it makes extensive patches, as seen on the rock on the left. The close-up on the right shows that its surface is smooth, not cracked like that of V maura, and has tiny black dots which are the perithecia or fruit-bodies.
Back at the top of the shore we find another maritime lichen, Lichina confinis (left), looking like a stubby seaweed with its club-shaped branches making a sward of uniform height. On the right is a real seaweed, Channelled Wrack or Pelvetia canaliculata, the highest up the shore of the common brown seaweeds, occurring around the high-tide mark. This plant is like a lichen in reverse, since it is an alga containing a fungus whereas a lichen is a fungus containing an alga.
These tiny shellfish shelter in old barnacle shells at low tide. They appear to be the young of a species of Littorina (winkles). The lowest barnacle is still intact and can be recogised as Chthamalus stellatus. It has black pits visible in its shell, which are the perithecia of a lichen from the group Collemopsidium foveolatum agg. The rest of the lichen is immersed in the shell.
Back on land, this Hartstongue Fern in the shelter of a gully has its last year's leaves still shiny green and one of them reversed to show the linear rows of spore-cases on the underside.
This lichen hanging in tufts from an old wall is Ramalina subfarinacea, the fifth Ramalina species we've had in the diary so far. On the right is an unusual specimen of Peltigera membranacea. I took its picture because I thought it might be something different, but it keys out to the very common P membranacea without any trouble. Differences from the normal form are: thallus not markedly veined above, rhizines only sparsely hairy, and the brownish thallus colour. The white on the thallus lobes is due to their dense covering of fine down.
Finally the liverwort Conocephalum conicum, which covers the ground on both the shady and sunny sides of a small waterfall not far from the shore. The long-stalked cones are produced in Spring, but the liverwort can be recognised at any time by its strong scent and the raised pores on its surface, visible as white dots in the RH picture, which lie within a network of hexagons about 1 mm or more across.
All photos and other content copyright © Carl Farmer