Introduction

Medicinal Lichens of North America

There is a low mist in the woods—

It is a good day to study lichens.

Henry David Thoreau

Well, any day is a good day to observe the lichens in your neighborhood. Rural or urban, desert or polar, on trees or rocks, on gravestones and monuments, they are everywhere! They favor gravestones, rock walls, cement sidewalks, telephone poles, traffic signs, rusty automobiles, windows, plastic, rubber, leather, and fence posts.

Lichens, along with mushrooms, molds, and yeasts, are members of the kingdom Fungi. Biologically, they are more closely related to humans than to plants. They are so unique they should be given their own kingdom or queendom—identifying them in terms of gender is also taxonomically challenging.

They are often neglected or ignored and have become to many humans an overlooked natural background in city and country. Lichens adapt to difficult ecologies, earning the term extremophiles.

Vincent Zonca (2023) offers his take on their role in our world:

Faceless, mineral and inert in appearance, lichen poses a moral and political problem: it inspires no spontaneous empathy. Like other “lower” beings, it has a hard time accommodating anthropomorphism . . . Must lichen be condemned to the scholarship of specialists or to our idealization of the Marginal and compassion for antiheroes?

The neglect of lichens is symptomatic of human estrangement from nature. In the mid 1970s I read E. F. Schumacher’s book (1973) Small Is Beautiful. It impacted me deeply on a personal level: how one’s individual actions can make a difference. During the same time period I was living in a hippy commune, and began to understand the benefits of cooperation, and symbiotic, mutualistic interactions and energetics.

Our community created a private school, and my godson was an early student. Our walks together in the boreal forest must have rubbed off, as he later completed his Ph.D. in lichenology from Duke University.

But in the past fifty years, the unbridled pursuits of capitalism, optimizing gross domestic product growth, burning of fossil fuels, destruction of old growth forests, and destructive globalization have led to the extinction of numerous species. At present, Earthlings collectively consume the equivalent of 2.8 hectares of land per person, meaning we use the equivalent of 1.8 Earths to meet our present demand. Clearly, this practice is not sustainable.

Sandra Lawrence (2022) notes, “The canaries in this particular coal mine are quietly slipping into unconsciousness and not enough of us seem to be noticing.”

Lichens are a metaphor for becoming more grounded, humble, and attuned to an awareness of the pressing need for a new ecology, and political change, by working on a local grounded level. This represents ancient wisdom, as well as a radical reactionary response. Lichens remind us of the need for positive environmental protection, and to learn lessons from history, not change them.

Lichens are both fragile and resistant. They have the capacity to adapt to changing environments yet are like the proverbial canary in the coal mine, foretelling impending danger. They grow slowly and are symbiotic, the exact opposite of Western society. “They invite us to leave the beaten paths, to cultivate slowness and patience to counter a consumerist ideal based on desires and the acceleration of time, to adopt a model of minimal growth to counter the hubris of exponential growth at any price” (Zonca 2023).

A collaboration between algae, cyanobacteria, bacteria, and fungi gives lichens the ability to survive and thrive in extreme conditions of temperature and lack of moisture.

Some lichens thrive around hot springs at temperatures above 200oC (392oF), while others thrive in cold extremes of minus 60oC (–76oF). The orange-colored elegant sunburst (Xanthoria elegans) lichen grows on rocks at 7,000 meters and survived eighteen months on the walls of the International Space Station. Lichens have been found as soon as four years after flowing lava has cooled.

They can go dormant during periods of drought and revive when moisture is available, swelling up and turning green as they absorb thirty times their weight in water! This process was named reviviscence by Claude Bernard in the mid-nineteenth century, and later anabiosis.

Today, the term poikilohydric is used, meaning the water regulation and content depend upon the lichen’s environment. In hot, dry climates, lichens absorb small amounts of moisture from the atmosphere, as too high a content of water might simmer their tissue or interfere with carbon dioxide and nitrogen exchange.

The life span of lichens is difficult to determine. In the arctic and Antarctica, lichen growth may measure in the millimeters, while tropical lichens can grow several centimeters annually. It appears the slowest growers live longer, and some species, such as temperate-zone Parmelia, live only a decade or two. Semidormant lichens have been found in the arctic from 3,700 to 9,000 years old, while endoliths in Antarctic glacial ice may be up to 100,000 years old (Margesin et al., eds. 2008).

Some withered deciduous ones are left to rustle, and our cold immortal evergreens. Some lichenous thoughts still adhere to us.

Henry David Thoreau

The term lichen may derive from the ancient Greek word leikhën, meaning “to lick.” Leprosy, “what eats around itself,” refers to this skin-related ailment’s peeling appearance. The Latin lîchen may have derived from an ancient Greek word, and means “ringworm,” a fungal skin infection.

This version of lichen was described more specifically by Hippocrates ( 460–371 BCE). Aulus Cornelius Celsus, a Roman physician, also used the term for “the papulae of an eroding, blistering eruption.” Pliny the Elder described lichen as “synonymous with the impetigo of the Latins.” Galen (129–217 BCE) described lichen as “a roughness of the skin, attended with much itching” (Zaghi and Griffin 2016).

Leikhën is also the root of word likanos, meaning “the finger one licks,” or the index finger. In turn, this name was given to a string on a lyre specifically played by the index finger.

The genus Lepraria and the term leprosy derive from the Greek lepein, “to peel.” The autoimmune skin diseases lichen planus and lichen sclerosus stem from this root word. Even the Latin word lepra was denigrated by early Christian writers who used it to mean sin or heresy. No surprise there. On the other hand, it is related to the word “liken,” which suggests comradeship, connectedness, contact, and affection.

But exactly how would one define the relationship between algae, cyanobacteria, and fungi?

Over time, various theories and metaphors have been proposed. Trevor Goward, a lichenologist at the University of British Columbia, suggests, tongue in cheek, that lichens are fungi that discovered agriculture. Other authors suggest lichen fungi are parasites that may become benevolent, or that lichen algae are solar panels for fungi—or the reverse, that fungi are greenhouses for algae growth.

One advantage of cyanobacteria is that it can fix atmospheric nitrogen into a useable form for plants and animals, leading to producing sugars. The fungi provide structure and protection.

Cyanobacteria, like humans, have a circadian rhythm. That is, they have a need for sleep, rest, and a restorative aspect. In humans, the recent discovery of the glymphatic tissue in the brain, with its ability to remove toxins from the brain during sleep, explains in part the ever-increasing levels of reduced mental health and increased levels of chronic neurological diseases. In terms of such rhythms, polar lichens possess internal clocks that help shift their adjustment to seasonal levels of sunlight.

Early authors depicted the fungus in the lichen as a sort of slave driver, or parasitic, describing the condition as helotism. Cooke (1893) wrote about the fungus, “It surrounds them as a spider its prey, with a fibrous net of narrow meshes, which is gradually converted into an impenetrable covering; but whilst the spider sucks its prey and leaves it dead, the fungus incites the algae found in its net to more rapid activity, nay, to more vigorous increase.”

Lichens have a unique capacity to live where no other organisms can survive. The algae provide carbohydrates through photosynthesis, and the fungi in turn provide water, minerals and a complex thallus (a plant part that does not differentiate stems and leaves, lacks true roots, and lacks a vascular system) that prevents algae from drying out. Lichens with algae cannot absorb nitrogen and depend upon their rock or tree to make amino acids. How the algal, bacterial, and fungal elements communicate remains a mystery.

Lichens are fascinating in that they create soil, by the breakdown of rocks, and provide plants with a means of growth. Lichens produce acid that breaks down stone, creating depressions to anchor themselves. When these fine crystals combine with decayed lichens, the first nitrogen-rich soil is formed.

Lichens are long-lived. The round-patched, light-green map lichens are up to five thousand years old. Yellow map lichen (Rhizocarpon geographicum) is estimated to live up to 8,600 years.