A series following the 72 British mini-seasons of Nature’s Calendar by Kiera Chapman, Lulah Ellender, Rowan Jaines and Rebecca Warren. 

Dear Readers, a frosty morning presents a great opportunity to have a look for lichens: they are everywhere but, like mosses, they are often overlooked, because they are not as colourful or as showy as flowering plants. Hah! They are complicated, multi-faceted organisms, as we shall see below. They can give an indication of how clean the air is – look at this headstone from Milborne St Andrew, the sheer variety of lichens tells you something about both which species can survive, and how old the stone is.

Headstone in St Andrews’s churchyard, Milborne St Andrew

Plus, unlikely as it seems, lichen is the food for the caterpillar of the Marbled Beauty moth, as I described here

Marbled Beauty caterpillar

Marbled Beauty (Cryphia domestica)

Sometimes we just need to slow down a bit to admire what’s under our noses. And if not now, when? We haven’t got forever, you know.

And now, let’s see what I had to say about lichens back in 2024.

In her piece in Nature’s Calendar, Kiera Chapman tells us that there are 2,300 species of lichen in the UK. They vary enormously, from flat crusts like the ones above to organisms that look more like coral. They live in habitats as varied as deserts and rainforests, and can vary in size from less than a millimetre to two metres.

What is a lichen, though? It’s not a single organism but an association between at least two organisms – the mycobiont, which is a fungus, and the photobiont, which gathers energy from light via photosynthesis and can be an alga or a bacteria. The relationship between the two has been debated for a century and a half. The whole idea of mutualism between two species (where both benefit from the association) was pooh-poohed at first, with the hypothesis being that the fungus ‘captured’ the alga/bacterium and held it captive, like an ogre sequestering Rapunzel in a tower. In fact, there is still some discussion about how to classify the relationship: it may appear that the fungus is parasitizing the other organism, but some photobionts can’t now exist without the fungus. It’s clearly a complex relationship that varies in emphasis from species to species.

Ash trunks with lichen (probably black apothecia)

Chapman discusses two different artworks that are based on lichen. First up is a monumental work by Klaus Daven on the Vouglans Dam in the Jura region of France. It was created by a process known as ‘reverse graffiti’, whereby a pressure washer blasted off most of the lichen and algae in order to create an image of a forest. It was sponsored by the electricity company and a company that makes power washers. For Chapman, and for me, it feels slightly uncomfortable – destroying one set of lifeforms to make images of others seems the opposite of environmentally friendly, however impressive the final results are.

The Vouglans Dan with Dauven’s image of the Jura forest (Thilo Parg, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0&gt;, via Wikimedia Commons)

The second work is by German artist Hubert Fenzl, who uses sustainably harvested Claydonia lichen to make artworks that will live indoors for years. His ‘Rainforest’, shown below, uses the lichen to form a birds-eye view of a forest, surrounded by a menacing red area that seems to surround and encroach upon it. As Chapman points out, the combination of a human artistic vision and this natural material asks questions about our care of the forests. There is also none of the grandiosity of the dam project. I know which I prefer.

Rainforest by Hubert Fenzl (From https://www.hubert-fenzl.de/informationen/gestaltungsmaterial-cladonia-stellaris-flechte/)

I was also very heartened to learn from my RHS magazine this week that biology studen Lottie Cavanagh-Sweeney has been commissioned by the British Lichen Society to make a Lichen Trail at the RHS garden at Rosemoor in Devon. Magnifying glasses are provided to examine some of the smaller lichens, and you can download the trail to a smartphone. One of the featured lichens is the rare Tree Lungwort (Lobaria pulmonaria) which Fay Newbery, a plant pathologist, describes as ‘green when wet, brown and crinkly when dry.’

Just look at this gorgeous organism!

Tree Lungwort (Lobaria pulmonaria) Photo By Bernd Haynold – Self-photographed, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3320107

The elephant in the room, however, as with so many other things, is climate change. An article in New Scientist in 2022 suggested that it had taken a million years for the algae that form the photosynthetic part of the lichen partnership to evolve to cope with 1° Centigrade of warming. They are also not fond of air pollution – the variety of lichens on the headstone at the top of the page indicates that it’s in a rural area with relatively clean air. Still, let’s not become too downhearted just yet – lichens have been here a long time, and who knows how resilient they might prove to be? In the meantime, let’s keep our eyes open for these overlooked organisms.