The Lichen List: Xanthoria parietina

Now that the leaves are gone from the trees, the lichens that festoon trunks and branches are nicely visible, and I've been working to identify them. A few are easy. This is Xanthoria parietina, which is a very common species across the UK. Xanthoria means "golden-yellow" — certainly a good descriptor of this lichen, particularly when it's in a sunny spot like this, on a branch of our apple tree. In heavy shade, it's grey-green! One of the reasons that this species is so common is that it can tolerate high nitrogen and sulphur dioxide pollution, which is something that many lichens can't. And since our garden is surrounded by plenty of well-sprayed farm fields, our lichens are exposed to plenty of nitrogen. This is one of the first lichens I learned as a neophyte lichenologist, and I find it nearly everywhere I look. It's even widespread in towns and cities, particularly in areas where birds perch and poop.

Up close, you can see some of the key features that distinguish this lichen from some similar ones. The lobes at the edges of the lichen are generally flat (though sometimes turned up at the edges) and very wide — as much as 7mm (nearly a quarter of an inch) on the biggest lobes. That may not seem like much, but for a lichen, that's huge! The apothecia (those small, bright orange bits that look sort of like tiny, well-done pancakes) are numerous, relatively flat and unstalked, and clustered in the middle of the lichen. According to my lichen book, the centers of old specimens often die out, so I guess all of ours are relatively young colonies, as I have yet to find any with dead centers.