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.
Author
- Nicholas Carter
Lecturer in Physical Geography, University of Oxford
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.
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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.
Verrucaria baldensis is an endolithic lichen that embeds in stone. At the surface of the stone, it can leave pits where its fruiting bodies detach. I call it the Moon Lichen because that's exactly what it looks like up close; the surface of the Moon, the pits becoming craters. But when you look at it from above, or even in cross-section to see how it embeds in the stone, you'd be forgiven for thinking it had vanished, or was actually mainly stone. The relationship between the biology and the geology becomes so close that there seems good reason to consider the two together when observing it.
The moment stone is quarried or exposed in some other way, colonisation of its surface begins, by cyanobacteria, algae and so on. This means that when that stone finds its way into a wall, a building, a monument or sculpture somewhere it has already started transforming, metamorphosing into something that acts alive. And so, at the surface, the stone is taking in carbon dioxide from the atmosphere and replacing it with oxygen, contributing to our net zero aspirations.
And when a lichen forms on it, in time, that stone becomes part of the lichen, and so contributing to the biodiversity of the site. We don't see it, or think about it even, but it's happening. We just need to start seeing stone differently, dynamically, more than the mineral. For a Unesco World Heritage Site like Blenheim Palace, where I've been conducting lichen surveys and whose vision is partly to enhance the ecological value of the site, seeing stone in this way is highly beneficial.
Arguably, much of how we define something depends on our relationship with it and how we choose to see it. How we value the living in relation to the non-living plays out in how we define lichens; we need to acknowledge the importance and value of both. In doing so, we are altering our perception of stone and our relationship with it. For there to be effective conservation, we need to value stone and other non-living entities because of the close relationships involved.
The reverse situation also occurs. In the field of heritage conservation, stone, the abiotic, relocated by humans, is often valued over and above the biotic, for example lichens, which can be found colonising and occupying it. We tend to want to preserve rather than conserve stone when it comes to cultural monuments and structures, so huge sums of money are spent on cleaning historic buildings and sculptures, including on the use of biocides, many of which can be dangerous for human health and the environment .
Metaphors for resistance and resilience
It's when we start to understand the cultural contributions as well as the ecological and conservation benefits of lichens to heritage that we start to lean towards and come up with more effective nature-based solutions in relation to the deterioration of stonework.
After all, lichens occur in our folklore, and have stories to tell , and so bring a flavour of intangible cultural heritage, as well as sometimes protecting stone surfaces from other deteriorative agents. What's interesting here is that heritage scientists have often talked about stone in human terms, when diagnosing decay for example. So stone forms blisters and has a memory even , storing past traumas related to environmental pollution.
And lichens are also influencing a cultural and artistic re-evaluation of stone, such that contemporary artists and writers are exploring the symbiotic relationships lichens have with stone, viewing them as metaphors for resistance, resilience and interconnection. In this way, lichens highlight stone's living narrative, bridging biology and geology in relation to the human condition.
There's an interesting parallel to draw here in terms of life defined by relationships. A developing theme in anthropology focuses on the intra-actions among humans and the mineral world. In her article on this , Nadia Breda's ethnography discovers a European form of animism that "attributed subjectivity, intentionality, ability and agency to non-humans, revealing an interspecies network of relationships hidden by the western naturalistic worldview".
In the company of the Piave, an Italian river where water and stones were described by old gatherers as living beings, Breda signposts an anthropology of life where "stones are living in this moving world of humans, stones and water" in a world where "life is not an intrinsic property of objects but a condition of being dependent on the context, and vitality is not a property of isolated individuals, but of the total field or relationships in which they are interacting."
By observing lichens and listening to voices outside of a western perspective, we see stone as something more than lifeless, a way of reconnecting with the natural world - which we desperately need.
We form relationships and emotional attachments to the biological world with relative ease, but we need to nurture these connections with physical elements too, and not just when they hold cultural or symbolic significance. As such, we need to advocate for soil integrity, for example, as much as for saving endangered species. Ethical debates such as rights and conservation should not just focus on the biological, and what we see as the physical must be spoken about in terms of moral obligations.
Stone is significant to lichens as well as many human cultures, representing more than inert matter, carrying meaning, history and spiritual significance. Focusing too rigidly on a binary distinction obscures the integrated nature of ecosystems and diminishes these broader environmental and human connections, which can offer valuable insights into sustainability and environmental stewardship. This is less about making distinctions, but building more connections.
This article was a runner up in The Conversation Prize for writers , run in partnership with Faber and Curtis Brown.
Nicholas Carter does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
