“Anything so radical & ordinary stands for something.”
— Brenda Hillman, from Metaphor and Simile24 poems at years’ end

The growth forms of lichen are a kind of poetry: the filmy, powdery skin of the leprose variety clings to bark, the viscous mass of gelatinous lichen congeals on rock, the gossamer fingers of the byssoid grasping outward. Just as poetry enthralls the senses, lichens practically beg for visceral contact. Like poetic inspiration, they manifest in places both mundane and improbable—the bark and leaves of plants, the inside of rocks, man-made surfaces of concrete, glass, or plastic. Without roots, they embed themselves directly onto surfaces. Though most grow fewer than 5 millimeters per year, lichen cover almost 10% of all land on Earth, patterning the natural landscape like a motif.

Lichens are a composite, formed by two or more components. Most commonly, this involves a mycobiont, the fungal partner, and a photobiont, the photosynthetic partner such as algae or cyanobacteria. The mycobiont’s hyphae, threads of a root-like fungal network, extend themselves to weave around cells of the photobiont. This combined biomass eventually differentiates into the thallus, a lichen’s principal body. 

While most plants wear a waxy protective cuticle over their leaves, lichens are entirely exposed to the elements. Just as the meaning of each word in a poem depends on its context, a lichen’s physiology is supremely responsive to its environment. Their bodies receive our contributions to the environment, too, whether they’re absorbing alkaline dust from mined quarries, radionuclides from nuclear accidents, or hydrocarbons from pesticides.

Just as poetry enthralls the senses, lichens practically beg for visceral contact

But the lichen body absorbs more than just chemicals: throughout their natural history, lichens, like poetry, have embodied the sociocultural milieu around them. Over the last 200 years, lichen have acted as a microcosm of our own social relations in a world of power, intimacy, interdependence, and community. In seeking to understand lichen, we ask: What do we mean to one another? What will we, or can we, become together? In our attempts to understand lichen biology, we reveal how we relate to one another — between species and within our own. 

Power

When such different beings join themselves so closely, our first instinct seems to be to classify their relationship as either love or power. Over the last century, the relationship between mycobiont and photobiont have been lord and serf, enamored lovers, tentative business partners, and a shotgun marriage. It’s as if their proximity implies that the logical next move is intimacy or violence. (Acting classes refer to the distance between characters standing within arm’s reach from one another as the “kiss or kill” range.) Or, as singer Janelle Monae puts it in their song “Screwed”:

“Everything is about sex, except sex, which is about power./Power is just sex, so ask yourself: who’s screwing you?”

This dynamic of hierarchy and exploitation reflects the first recognition of lichens as composite organisms more than a century ago. Lichens were categorized as plants until 1869, when botanist Simon Schwendener proposed that they were in fact a form of controlled parasitism between a fungus and algae. Lichens were not “individuals in the usual sense of the term,” but “colonies.” Schwendener painted the association between fungus and algae in highly specific social imagery—the “master” fungus enslaved algal cells, compelling them to produce nutrients while being kept in perpetual captivity.

Schwendener was immediately met with fierce opposition. Lichen taxonomists ridiculed the premise of lichens as two organisms in a parasitic relationship, calling it “doomed” and a “baseless fabric of a vision.” The controversy persisted for over twenty years, even as empirical evidence for lichens as a fungus-algae composite increased. 

What about Schwendener’s hypothesis had provoked such rage and indignation? The specific social context at the time plays a key role. Just a decade earlier, Charles Darwin’s The Origin of Species had seized the scientific and social zeitgeist. In the Darwinist paradigm of life, survival and progress emerged from competition, which was both natural and brutal:

“…from the war of nature, from famine and death, the most exalted object…namely, the production of the higher animals, directly follows.”

The proponents of Social Darwinism quickly co-opted this principle to apply it to human society. Sociologist Herbert Spencer, who first used the term “the survival of the fittest,” believed that those who emerged on top of the social hierarchy were the best people to govern it. Rhetoric surrounding natural selection justified a push toward laissez-faire capitalism and the poverty, inequality, and colonialism it promoted. This idea emphasized the meritocratic qualities of individualistic competition, in direct opposition to Schwendener’s portrait of exploitative hierarchy. 

One objection came from James Crombie, an English reverend studying the British Museum’s lichen collection. Both Schwendener and Crombie used charged socio-political rhetoric to describe the lichen, invoking power, property, class, and hierarchy to illustrate two conflicting views of society. Schwendener characterizes the fungus as parasitic, and specifically as one “with the wisdom of statesmen.” Crombie appeals to lichen autonomy with private property, to land and title deeds — the typical entitlements of the landed gentry: 

“Of late years…the lichen territory has gradually been enlarged at the expense of its neighbors. Alike from the algae and the fungi it has made various important acquisitions, which of right belonged to it all along…Very recently, however, a theory has been started, which, should it be accepted, would virtually deprive lichens of the position…assigned to them in the vegetable kingdom.”

What Crombie saw as the natural birthright of class and status, Schwendener, in contrast, portrays as entirely contingent on an unequal arrangement. When the fungal component of lichen was forcibly separated from the algae, the algae survived but the fungus withered. The fungus had sacrificed itself to suit this arrangement so completely, that it became entirely “accustomed to live upon the work of others,” according to Schwendener. Schwendener’s imagery of a parasitic ruling class living off exploited labor is a distinctly Marxist view of class relations, suggesting that power and wealth are not rightfully earned, but gained through the oppression of others. This hypothesis may have struck a nerve in the age of empires shaken by uprisings and revolutions, like the Haitian Revolution in 1804, the Year of Revolution throughout Europe in 1848, and the First War for Indian Independence in 1857.

Crombie railed against the specter of the composite lichen for 15 years. He sent letters about the ridiculousness of master fungi and algal slaves to scientific journals, professional societies, and the Encyclopedia Britannica. In an 1874 letter to a journal, Crombie asserted that lichens were being “ruthlessly deprived of their autonomous existence”, indignant that they were, “as if by the stroke of a magician’s wand” transformed into “master fungus and imprisoned algal slaves.” Even after almost a decade, his 1882 contributions to the lichen entry in the 9th edition of the Encyclopedia Britannica continued to deride Schwendener’s work as objectionable, insisting that “as there is no algal in the lichen, so neither is there any fungus.” The anxiety that it provoked seems less about the lichen per se, and more about how lichens challenged the prevailing categorization and understanding underlying Crombie’s worldview. In this way, the lichens embodied their first social form. The intense struggle over how lichens should be defined represented the larger conflict over how human society should be organized.

Dependence

Schwendener’s rhetorical framing of lichens was a powerful catalyst for thinking about the different ways in which the natural world was shaped by relationships between organisms—including relationships much less adversarial than Schwendener’s master-slave dynamic. As scientists in the 1870s followed the threads that linked the natural world together, they found diverse networks of interactions. A new paradigm of social interactions in the natural world began to emerge. Natural interactions of all kinds were characterized — antagonistic or cooperative, permanent or fleeting. Like relationships in human society, they could be complex, could assume varying degrees of intimacy, and above all, could be profoundly meaningful to the lives they entwined together. Belgian zoologist Pierre-Joseph van Beneden opined in 1876 that free-living animals and parasites were only separated by “insensible gradations of difference”:

“Many of them are towed along by others…some take advantage of some assistance which their companions can give them; some afford each other an asylum, and some are found which have sympathetic bonds which always draw them together”

With this perspective, other experimentalists reexamined Schwendener’s characterization of fungus-algae serfdom. German botanist Albert Frank’s observations showed that both fungus and algae exchanged resources and contributed to their survival together. He called this mutually beneficial relationship “symbiosis” to represent a more general phenomenon of interspecies coexistence, believing that the fungus’ dependence on the algae did not necessarily mean it was parasitic. Frank’s observations led to newly recognized forms of cooperative symbiosis, such as mutualism, a form of symbiosis where both organisms benefit, or commensalism, where one organism benefits from an association without affecting the other.

By the end of the 1890s, lichens had redefined how we thought animals survive. Survival was both an individualistic, zero-sum competition, and a process that emerged from connection: networks of resource exchange and production, shared interests, protection and cooperation. Dependence was the default. The lichen’s amalgamated body made its intricate interactions tangible —a reminder that no creature truly exists on its own.

Embodiment and Experience

Many organisms live symbiotically among lichen. In addition to multiple strains of algae living together within one lichen, research from the last decade has revealed lichens that cultivate their own microbiome of distinct bacterial communities. Over 1800 species of non-lichen forming fungi have been found living in or on lichen, as well as a relatively under-explored collection of protists and viruses. Some researchers think that these organisms are a core part of the lichen itself, challenging our understanding of lichens beyond the typical mycobiont-photobiont partnership.

But what does it mean to be a core part of a larger whole? Typically, we would take this to mean that these organisms are necessary to the lichen’s survival. And yet the algal component of a lichen, despite its ability to survive when isolated from the fungus, isn’t a lichen on its own. Terms used to describe symbiosis—mutualism, commensalism, parasitism—imply a kind of externality, that there are separate selves forming a connection. In his book Entangled Life, Merlin Sheldrake describes how lichens confound the notion of existing independently:

“Lichens are places where an organism unravels into an ecosystem and where an ecosystem congeals into an organism. They flicker between wholes and collections of parts.”

Lichens do not exist as disparate selves—their existence is, in itself, an emergent symbiotic phenomenon. Even the external contours of a lichen influence life around it. The architecture of lichen thallus provides microhabitats for bacteria to grow, entwining themselves around their aerial hyphae, or burrowing into cracks between their surface crust. Slime molds seem to form preferentially under a lichen’s fleshy lobes, while springtails and other arthropods graze on plains of bacterial biofilms growing on their sprawling surface.

With the ever-growing number of organisms that live in, around, and upon them, an increasingly well-accepted definition of lichens is that they are a “self-sustaining ecosystem”. 

According to linguist George Lakoff, the essence of metaphor is to understand and experience one kind of thing in terms of another; lichens are a conduit for this understanding. In the essay Queer Theory for Lichens, David Griffiths declares that we are all lichen: What we think of as a human “individual” is itself a multi-organismal amalgamation made of the bacteria living in our gut, the once free-living organelles in our cells, and the retroviral genetic elements embedded in our DNA. No creature truly exists on its own, but no creature exists as its own either.

Generating New Meaning

The thought of being an amalgamation, rather than an individual, is uneasy. To conquer sickness, for example, the common conception is to return to a “pure” healthy body free of whatever external invaders have corrupted it. But lichens hardly seem compromised by this state of unbounded existence. They cling to the barren surfaces of Antarctic tundra and embed themselves into the unforgiving dry rock of the Sonoran Desert. Even attached to the outside of the International Space Station for 18 months, exposed to the vacuum of space, radiation, and extreme temperatures, lichens greeted the sun’s radiation calmly and continued photosynthesizing.

In fact, their survivability is owed to their communal existence. Of over 700 metabolites that have been isolated from lichens, over 90% of them are only found within the symbioses. These metabolites confer tolerance to extreme stress, antibiotic activity, resistance to heavy metal toxicity, and protection from UV radiation—an incredibly versatile and adaptable metabolic repertoire that the individual components of a lichen would not be able to access on their own. 

In addition to resolutely adapting themselves to their environment, lichens also make the environment around them more habitable. They prevent desertification by stabilizing the soil crust, a tiny bulwark against oncoming hostility. Some tolerate pollution, fixing nitrogen and absorbing heavy metals from air and soil. Those growing on bare rock slowly weather it, drawing down atmospheric carbon that may ultimately be sequestered into the earth.

No creature truly exists on its own, but no creature exists as its own either.

On a biotechnological level, the lichen’s modular metabolism draws attention. Harnessing it would enable far more combinatorial biosynthetic possibilities, where each lichen component can contribute uniquely to a greater mission of the larger ensemble. Making bespoke artificial lichen could also act as a means to produce specific compounds without starting from scratch or create lichens with tunable material properties and morphologies to make new biomaterials. Engineering lichens that grow faster might make them a viable organism to help mitigate the pitfalls of the Anthropocene — growing barriers to prevent further desert encroachment, remediate heavily polluted areas, or deploying them on the newly exposed rock of melting glaciers to increase carbon fixation. As climate change and ecological degradation turns drylands into desert, leaves habitats mired in pollutants, and rising temperature melt glaciers, lichens could alleviate some of the most pressing challenges we face today.

Science, and synthetic biology in particular, generally assumes that humans control the non-human life that we seek to manipulate. But learning how to grow a lichen demands that we acknowledge the agencies of the non-human life involved. 

Even before they physically meet, the symbionts recognize each other. They draw together through elaborate chemical and molecular signals and begin changing on a molecular level prior to contact, adapting themselves to this new form of life. In from Metaphor and Simile24 poems at year’s end, the poet Brenda Hillman writes: “Some people think lichen looks dead but it is alive in its/dismantling”

As we confront the prospect of living through climate change, surviving increasingly harsh conditions of our own, what would we need to dismantle for us all to build something new? The process of engineering a lichen involves understanding the conditions under which the symbionts will form one, not the forcible stitching of components together like a fungal Frankenstein’s monster. What we want out of creating a lichen matters little if we do not understand what a lichen wants out of becoming one—learning how to grow a lichen means understanding how to build a community from the ground up.