When you tug on a single thing in nature, you find it attached to the entire universe.”

John Muir

When I was in university, I entered grad school with the intention of studying lichen. I found these multi-species organisms fascinating. As with another love of mine—water—these organisms could be found everywhere and yet remained mysterious and little understood, or appreciated (just like water). Lichen are ubiquitous; occurring nearly everywhere from the most mundane to the most exotic habitats. Lichen lives in your backyard, on the ground, pavement, rocks, tree bark and branches, rotting logs, and moss.

“A single Sugar Maple may be home to as many as twenty lichen species,” writes Joe Walewski, author of the guide book Lichens of the North Woods (Kollath & Stensaas Publishing, 2007).

But the professor I would have studied under had decided to retire and put me onto another professor who was researching zooplankton ecology. I ended up researching the dynamics of periphyton (attached algae) in streams (also very fascinating!). I wrote some papers on the effects of current on the colonizing strategies of periphyton communities on new surfaces. Oddly enough, as I look at it now, I see several similarities between periphyton and lichen that are also primary colonizers (of rocks and other surfaces).

My fascination for lichen never abated, despite (or was it because of?) what little I knew about them. I didn’t know that in the 1700s Carl Linnaeus, founder of taxonomy, called lichens “poor trash of vegetation.” I didn’t know that Linnaeus assigned just one genus to this organism.

Thanks to the study of this “trash vegetation” this one genus—Lichen—has since expanded to encompass hundreds of genera and over 14,000 species of lichens. Ruby-throated Hummingbirds use Shield Lichen (Parmedia) in nest construction for camouflage; Warblers weave strands of draping Beard Lichens (Usnea) in their nests; White-tailed deer and flying squirrels eat lichens as do a myriad of tiny insects and slugs. Lichen are a staple for caribou who eat an average of three kilograms daily. According to Lazarus Sittichinli of the Gwich’in of the Northwest Territories, lichen takes a long time to grow; if you eat animals that eat willow, like moose, you will get hungry more quickly than eating animals that eat lichen, like caribou. Reindeer lichen (white moss or uudeezhu’ in Gwich’in) can be boiled to make a tea; Mary Kendi of Fort McPherson and Elizabeth Greenland agreed that it was good for stomach and chest pains.

Lichens are early succession primary sere colonists of rocks, preparing them for mosses, grasses and ultimately trees.

Because lichens efficiently collect airborne substances, they help recycle chemicals in the air into the soil. Because of this, lichen can be used as bio-indicators to gauge air quality and act as sentinels of air contamination. Poor lichen diversity and abundance may signal instances of air pollution.

Lichens come in three major types or forms: fruticose, crustose, and foliose. Fruticose lichen form bushy growths, sometimes with erect branches or tufted and draping. Fruticose lichen are distinguished by often having stalks (podetia) common in the Pixie Cups (Cladonia). Crustose lichen often look like spray paint, with medulla (lower surface) directly adhering to the substrate and blending in (e.g. Shield Lichen). Foliose lichen resemble leafy growths, divided by lobes that may end in apothecia (the fungal sexual apparatus) and with lower surface often differently coloured than the top surface. Typically, rhizines anchor this lichen to the surface (e.g. pelt lichen).

Types of Lichen Habitat

The Lichen is all about relationship—with itself (between its fungus and alga self)—but also with the substrate, whether living or not, on which it colonizes. Important features of the substrate to the lichen include its texture, moisture retention, and chemistry. The three main types of substrate include ground, rock, and trees.

Ground Substrates

The ground includes soil, sand, mosses and decomposing logs. The hyphae produced by lichen help stabilize and fertilize the soil with organic matter and nitrogen. Lichen that are light-coloured help keep the soil cool by reflecting heat. They also trap dust and act as substrates for other living things.

Rock Substrates

These include cliffs, talus, pebbles and boulders, as well as concrete and shingles. They are often found among the mosses that also colonize these same surfaces. Lichens grow among the rock crystals, helping to break down surfaces for mosses and other colonizers.

Tree Substrates

Lichen that grow on conifers and deciduous trees, are different based on their different surface textures, chemistry, light and moisture. Conifer bark, for instance, is rich in organic resins and gums, and is acidic. The canopy of a conifer is also more dense than most deciduous trees; this prevents some light from penetrating to the trunk. The sloping nature of spruce and fir trees also allows rain to fall to the forest floor rather than run down the trunk as it readily does on a deciduous tree. Anyone caught in a rainstorm, like me, will vouch for his difference.

As trees age, so does their bark. The bark of a sugar maple, for instance, is smooth when the tree is young; with age it softens, cracks and forms furrows that ooze alkaline nitrogenous compounds. Walewski tells us that older trees have a greater diversity of lichens. “Elm and poplar bark are low in acidity, stable and fairly absorbent. Oak, hickory and linden have hard, rough, acidic bark and host different [lichen]. Beech and other trees with smooth, living, green bark are home to yet another community of lichens.”

The Symbiotic Relationship of Lichen

As a writer, I see lichens as a cooperative  character; a tight pair of characters, really. Lichens are a complex symbiotic association of two or more fungi and algae (some also partner up with a yeast). The algae in lichens (called phycobiont or photobiont) photosynthesize and the fungus (mycobiont) provides protection for the photobiont. The fungus is commonly a member of the Ascomycetes, which include cup fungi, lobster fungi and morels. The most common algal partner is the unicellular alga Trebouxia and filamentous alga Tentepohlia. Sometimes a blue-green (Nostoc).

Walewski suggests that a lichen is not so much an organism as a lifestyle. They are Nature in miniature. And highly successful, given that lichen have populated the entire planet. Eight to ten percent of terrestrial ecosystems are thought to be dominated by lichen.

Both the algae and fungus absorb water, minerals, and pollutants from the air, through rain and dust. In sexual reproduction, the mycobiont produces fruiting bodies, often cup-shaped, called apothecia that release ascospores. The spores must find a compatible photobiont to create a lichen. They depend on each other for resources—from food to shelter and protection.

Lichen Reproduction

Lichens spread throughout the environment by reproducing both sexually and non-sexually. Justin Anthony Groves at Whiteknights biodiversity tells us that lichen reproduction: “is no simple matter; only the fungus of the lichen reproduces sexually.”

Lichen Sexual Reproduction:

Apothecia are disc or cup-shaped reproductive structures formed by the fungus part of the lichen. Spores develop in them and are then forcefully ejected or washed out and dispersed into the environment. One of two things must happen to successfully reproduce this way: the spore must land in a place where its algal partner exists in a free state; the spore may land on another lichen where the fungus (like a parasite) takes over the phycobiont of the existing lichen.

Producing units of dispersal that contain both fungus and alga would assure and speed up colonization of new sites. This is precisely what lichens do in their several techniques of asexual reproduction and propagule dispersal.

Lichen Asexual Dispersal:

Lichens have at least six ways they can disperse without the need for sexual reproduction, including the production of: 1) Fragmentation; 2) Squamules; 3) Isidia; 4) Soredia; 5) Phyllidia and Folioles; and 6) Conidia.

The lichen makes more of itself as fragments of the thallus break off and are often carried off by animals.

Some lichens have squamules (scales) on their thallus or produce them on structures called podetia (stalks, particularly of Cladonia lichen). The squamules break away to be distributed by animals or wind.

Specialized asexual structures called Isidia (peg-like outgrowths from the upper cortex of the main thallus) or clusters of Soredia (a dust like material usually on the lobe margins that contain algal cells wrapped in fungal hyphae) break off and are transported some distance by wind, rain and animals. Both Isidia and Soredia are bundles of photobiont cells bound up in fungal cells.

I saw a good example in the Trent Nature Sanctuary of soredia and isidia in the scaly thallus lobes of Cladonia chlorophaea after a dry spell followed by a light rain.

Phyllidia are small, leaf-like or scale-like outgrowths from a foliose thallus, constricted at the point of attachment and readily detached and dispersed by wind or animals. Folioles, or lobules, are similar outgrowths though less constricted. Both are considered leaf-like, flattened isidia.

Some lichen (mostly fruticose lichen) produce an outgrowth from the thallus in the form of a stalk or podetium. The Mealy Pixie Cup flask-like stalk bears a cup-like structure, a hymenial disc (apothecium) with pycnidia around its rim. The pycnidia contain conidia which are asexual fungal spores.

FRUTICOSE: Common and Lipstick Powderhorn—Cladonia coniocraea and C. macilenta

I found these two powderhorn lichens on decaying cedar stumps and logs in the forest swamp of the Trent Forest Sanctuary in the Kawarthas of Ontario. Both prefer moist and shady habitats. The Common Powderhorn is known to tolerate air pollution and appears to thrive in urban areas.

The Common Powderhorn is fruticose with two types of vegetative (thallus) forms: 1) flat, overlapping leaf-like scales (squamules); and 2) grayish-green slender unbranched stalks (podetia) that taper to a point or a very small cup. The upper two-thirds of the podetia is mealy with the covering of soredia (reproductive cluster of algal cells wrapped in fungal filaments). I saw no disk-shaped apothecia (cup-shaped fungal reproductive structure that produces spores). I’m told they are rare and, if they occur, are brown and sit on the top of the stalk. The Lipstick Powderhorn is a different thing, though…

Where the Common Powderhorn stalk tapers to an end with a slender glandular cup of the same colour, the Lipstick Powderhorn has a finely scaled stalk and several support a blunt red tip, the apothecium. Notice also the extensive squamules along the stalk (podetium) of the Lipstick Powderhorn. The squamules break away to be carried away by rain, wind or animals.

 

FRUTICOSE: Mealy Pixie Cup—Cladonia chlorophaea

The first time I found this lichen was on an old shaded cedar log in a mixed cedar forest. The second time I saw it was on the ground in a sunny place on a river bank in the Kawarthas on Ontario. As with similar trumpet lichen (Cladonia fimbriata), this lichen forms fruticose pale green goblet-shaped cups on stalks that rise from a patchy scaly mat. The Pixie Cup differs from the trumpet lichen by its wider cup and brownish crenulations (the pycnidia) on the edge of the cups.

Walewski tells us that this lichen grows on wood, bark, rock or soil in full sun or shade. The two habitats I found the Mealy Pixie Cup testify to its adaptability.

According to Walewski, the splash cups help the lichen reproduce. As rainwater splashes into the cup, spores from the apothecia (specifically, the pycnidia on the tip of the cup) are forcefully ejected, sailing to another place to colonize.

FOLIOSE: Many-Fruited Pelt—Peltigera polydactylon

I found this lichen growing among moss on rocks and boulders and the ground in several mixed cedar forests in the Kawarthas. This lichen spreads an undulating foliose brown mat (thallus) that forms upturned lobes with lighter saddle-shaped red-brown projections (apothecia). “As the name implies,” writes Walewski, “there are many fruiting bodies—apothecia—on the lobe margins.” Others describe these projections of the thallus into apothecia as fingers with bright red-orange to reddish-brown varnished finger nails. These apothecia are the reproductive structures for the fungal component or mycobiont. The tiny spores are released from the apothecia and fall to the ground and if they encounter the free-living Nostoc [a blue-green alga] will then grow into a new lichen. As I mentioned before, this seems a touch and go way to reproduce. Luckily the pelt lichen has more ways to reproduce.

I noticed Phyllidia and Folioles or “lobules” on the edges of the lobed thallus as well as what might have been Isidia (specialized outgrowths) of clusters of Soredia on the edges for easy dispersal. All of these asexual modes of reproduction provide all that’s necessary to grow another organism.

FOLIOSE: Star-Rosette Lichen—Physcia stellaris

I found this lichen on several Poplars, Elms and Buckthorns in the mixed forests and open thickets of the Kawarthas. They occurred mostly on branches and twigs. As the name suggests, the thallus forms a foliose rosette-shape that contains small dark brown disks (apothecia) that carry spores.

FRUTICOSE: Beard Lichen—Usnia sp.

I found this beautiful lichen colonizing a downed poplar tree in the cedar swamp forest in the Kawarthas. This lichen formed densely long-branched tufts and is considered pollution sensitive. Usually found high in the crown of trees, its branching form is suggested to reduce drag from the wind. Others suggest that branching has more to do with capturing light and carbon dioxide.

FOLIOSE: Bottlebrush Shield Lichen—Parmelia sulcata

I found this foliose pale gray lichen colonizing an old birch log in a cedar forest. Its thallus is dimpled with depressions and lower surface is black with unbranched rhyzines. Shield lichen may be the most common lichens in the Kawarthas. They are the first organisms to colonize trees (and even picnic tables!). Ruby-throated hummingbirds are known to camouflage their nests with bits of Parmelia.

CRUSTOSE: Fluffy Dust Lichen—Lepraria lobificans (finkii)

The bark of several trees in the local Kawartha forests were covered in colonies of Fluffy Dust Lichen, including oak, poplar, cedar and ash trees. As the name suggests, this dust lichen resembles green-gray granular dust or powder is if “spray-painted” on the tree bark. This lichen is common on many tree bases as well as shaded rock. If you’re lucky you may see dull, even or wrinkled soredia.

Fluffy Dust Lichen is widely distributed in the world and likes to grow on soil, over mosses, on bark where I see it most of the time, in moderately shaded and dry areas and on rock overhangs.

CRUSTOSE: Mapledust Lichen—Lecanora thysanophora

Many of the sugar maples in the local forest here in the Kawarthas are colonized by this crustose lichen. The best example of Mapledust’s yellowish-green fuzzy-dusty mat can be found on the smooth bark of a young maple tree. Mapledust (which also colonizes beech, oak and basswood, can be distinguished from Dust Lichen (Lepraria) by its white webby margin. The white edges are the fungal partner and the granular green surface are largely the algal partner. As the maple tree ages, its bark starts to ooze alkaline, nitrogenous compounds; these altering conditions create a more diverse community of lichen and mosses.

I found a good example of aging bark’s creation of greater diversity with an older white birch tree in a nearby swamp forest.

BIRCH LICHEN COMMUNITY

Remembering what Walewski said about the single sugar maple, I noticed the diverse lichen and moss community on an old white birch tree in the Trent Nature Sanctuary cedar-birch forest. I noticed several different lichens and several mosses in different stages of growth. As I strolled out of the dense forest that day, I reflected on Nature’s fractal arrangement: as I peered closer at the birch bark encrustations, I saw how like a miniature forest—its own universe—this bark community was. Complete with lichen, moss, fungi, algae and various foraging creatures. It was an entire functioning ecosystem.

The more you look, the more you see.   

References:

Andre, Alestine and Alan Fehr. 2002. “Gwich’in Ethnobotany,” 2nd ed. Gwich’in Social and Cultural Institute and Aurora Research Insitute. 68pp.

Gilbert, O., 2000. “Lichens.” London: HarperCollins

Lastdragon.org. 2021. “Images of British Lichens: FAQ.” Online: http://www.lichens.lastdragon.org/faq/lichen_asexual_dispersal.html

Nash III, H.T., 2010. “Lichen Biology”. 2nd ed. New York: Cambridge University Press

Purvis, P., 2000. “Lichens.” London: The Natural History Museum

Ryan, B.D., Bungartz, F., & Nash III, T.H. (2002). Morphology and anatomy of the lichen thallus, in Nash III, T.H., Ryan, B.D., Gries, C., & Bungartz, F. (eds.) Lichen flora of the Greater Sonoran Desert Region, vol. 1, Arizona State University, Tempe, pp. 8–23.

Smith, C.W., Aptroot, A., Coppins, B.J., Fletcher, A., Gilbert, O.L., James, P.W., & Wolseley, P.A. (eds.) (2009). The lichens of Great Britain and Ireland, British Lichen Society, London.

Walewski, Joe. 2007. “Lichens of the North Woods.” Kollath & Stensaas Publishing, Duluth, MN.