Sunburst

I'm still feeling quite rough, and spending the entire morning on the computer doing financial admin didn't improve the situation. The weather was also pretty dreich, and by lunch time I was in a deep slough of despond.

At this point the sky lifted a little, and though you wouldn't describe it as a nice afternoon, I did think it was worth getting the macro and going for a short walk around the garden. There were a few flies about, though none of them was co-operative, or this post would probably centre on a tiny, furry, grey moth fly that was pinging around one of the wood piles. As it was I gave up on the skittish stuff, and went for the easier option of shooting some mosses and lichens.

One of the apple trees in the wild garden is absolutely laden with lichens, and I liked this twig because it's so busy with life. The main guy - yellow, with apothecia (fruiting bodies) that vary between cup-shaped and disc-like - is most probably Xanthoria parietina, if only on the basis that common things are commonest. This is popularly called the common orange lichen or the common sunburst lichen, and can be found on pretty much any tree or rock surface that is rich in nitrates.

Lichens are composite organisms, in which fungi live in symbiotic relationships with either algae or cyanobacteria. The latter (collectively known as photobionts) produce sugars by photosynthesis, which feed their fungal hosts. In Xanthoria parietina the photobiont is one of a group of algae which are all green; the yellow colouration comes from the chemical xanthorin, which is thought to be produced as a defence against UV radiation. Therefore the colour of a patch of this lichen can vary between green and yellow, depending how exposed it is to direct sunlight.

There is something else going on here though. As well as the greener areas of the sunburst lichen, there are some pale grey-green lobes with cilia on their margins, which belong to a different lichen. It looks like one of the Physcia species, and at a guess I'd say Physcia tenella, though there isn't much in this photo to go on. P. tenella, and its close cousin P. adscendens (very similar, but with lobes that curl right over to form hood shapes) are both very common on trees, but are rarely found on stone surfaces.