Lichens on stone, those “still explosions” as the great American poet Elizabeth Bishop named them, remain unseen to most, which is remarkable when you consider how commonplace they are.
It seems these ecologically and culturally significant whatever-they-ares unfairly fall victim to something akin to plant blindness, a known phenomenon and tendency of people to overlook plants, which many of us – when we first encounter lichens – identify them as, even though that’s not what they are at all.
Part of the problem is that they’re not studied in schools because they’re awkward outsiders and are not perceived to fit in with the objectives of the science curriculum.
So I was surprised to see lichens leap into the public imagination following the Just Stop Oil protest at Stonehenge at the summer solstice in June, 2024.
Much of the outrage seemed to be in reaction to a quote from one of the protesters about the stones being inert: “It’s time for us to think about what our civilisation will leave behind – what is our legacy? Standing inert for generations works well for stones – not climate policy.” Inert? “Well, what about the rare lichens growing on them?”, was the response from some people, seeing them as separate from the stone, and for others more important even.
English Heritage, the current custodians of Stonehenge, talked about the stones as being “testament to the desire of people – from prehistoric times to today – to connect with nature, the Earth, the Sun and the Moon, as well as crucially, each other”.
And this very publication printed a response suggesting we should care more about the effects of climate change on our cultural heritage rather than the inconsequential actions of the Just Stop Oil protesters.
What’s more, a senior druid said he sympathised with the group’s message but was critical of their actions at the sacred site, warning against additional measures to protect the stones, given the summer solstice is the only day in the year that people can “connect with the stones and have a proper relationship”.
Relationship – a word that is often only reserved for connections between people, or people and animals, or animals and other animals, not people and what would otherwise be something seen – in western eyes at least – as abiotic, or non-living, lifeless, inert stones.
Or are they? For a lichenologist specialising in saxicolous (or stone) lichens, what’s particularly interesting to me is what lichens have to say about stone and its inertness, its lifelessness, the sweeping “abiotic” label that western thinking assigns to it.
This is because lichens are transforming our understanding of stone in both ecological and cultural contexts, and this could have major implications not only for the conservation of our cultural heritage, but also the broader field of conservation and how we understand and relate to the natural world.
What exactly is a lichen?
To start with, how we see lichens themselves is changing. Trying to agree on a definition of lichens that pushes them into one of science’s neat little cubby holes has proved as difficult as trying to distinguish stone from rock.
A symbiotic association between a fungus (a mycobiont) and a photosynthetic partner, usually an alga or a cyanobacterium (a photobiont), is where we’d got to. And to accommodate our Linnaean classification system of living things we’ve treated them as we would a single species, naming them after the fungus.
But the reality is, whereas all those other living things are assigned a single species name to sit at the end of a single branch of Darwin’s tree of life, lichens recline over several, perhaps many branches, giving us the side-eye. They simply don’t fit.
This has led some researchers to consider alternative ways of seeing them, including recently defining them as complex ecosystems due to the presence of additional microorganisms, including fungi and bacteria.
This sea change has been challenged, however, and the debate about “lichenhood” looks like it will go on as it has done since the mid-1860s.
More than their biology
The notion that lichens are ecosystems, or perhaps become ecosystems, really appeals to my geographer sensibilities. It frees the lichen from species-scale thinking yet doesn’t overshadow the symbiosis that also defines certain relationships involved. What we see and define as a lichen, can in fact become more complex over time.
One of the arguments against the idea that they are ecosystems is that it would require us to include the mineral, soil or plant substratum that the lichen grows on.
As scientist William Sanders writes, “For most biologists, a lichen removed from its substratum is still a lichen.”
I spend a lot of time looking at stone-dwelling lichens through a lens and under a microscope, and to me the co-habitational interplay between the stone, the lichen’s hyphae (or thread-like anchors) and its thallus (or main body) are intimate and dynamic, and ultimately a relationship that defines the lichen itself.
Lichens become more than their biology, mainly because they are in situ for such an extensive length of time and even often incorporate their substrate into their main body.
Depending on the environment, individuals can colonise rock and stone for decades, centuries, thousands of years even; it’s been proposed that some of the oldest found in northern Alaska are in the range of 10-11,500 years old.
And so, they blur the boundary between the biotic (living) and the abiotic (non-living), which occur on a continuum when you escape a species-scale view. (The Conversation)