Various lichen crowd over the gnarly bark of a red maple tree on a wet winter day, ON (photo by Nina Munteanu)
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After my fence post lichen study, I felt compelled to look for lichen everywhere else in my neighbourhood. The most prevalent surfaces I encountered during my walks were trees that lined my residential street, and most were sugar and red maple trees. The gnarly trunk of one particular red maple seemed to light up with brilliant yellow-orange patches of lichen, as if it was splashed with yellow paint. I leaned in closer and brought out my hand lens. Revealed before me on the trunk and branches was a profusion of shape and colour, a complex community of corticolous (bark-dwelling) lichen.
Sunburst and Candleflame Lichen shine in the sun, dominating the lower trunk of this red maple tree with colour, ON (photo by Nina Munteanu)
They formed an unruly horde of texture and colour, crowding each other like suburban housewives at a sale and covering every small valley and hill of bark in a miniature forest. Looking past the show-stopping bright orange rosettes, I took in the other lichen that ranged from blue-grey to grey-green and olive-green—and even flat white, like my favourite coffee!
Red maple trunk displaying a shaggy multi-coloured carpet of several lichen including the dull white of Whitewash Lichen, the bright yellow of Hooded Sunburst Lichen and Candleflame Lichen, and the ‘bulby trees’ of Hooded Rosette Lichen, ON (photo by Nina Munteanu)
I remembered a quote by lichenologist Joe Walewski, author of the guide book Lichens of the North Woods: “A single Sugar Maple may be home to as many as twenty lichen species.”
Physcia biziana, P. adscendens and Candelaria concolor lichens in dry conditions on red maple trunk, ON (photo by Nina Munteanu)
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Determined to identify as many species as I could, I set out to photograph them with my macro lens. When I returned home to study the images, my camera often found what my eye had missed. I first encountered the lichen in their dry forms and colours on an early winter day. Successive visits, particularly after snow or rain, revealed more intense colours in the wet, as the lichen showed off their photosynthesising algal partners. Some differences in appearance were quite dramatic.
Physcia biziana (with apothecia) and P. adscendens (bottom centre) along with Sunburst Lichen and Candleflame Lichen under wet conditions on red maple trunk, ON (photo by Nina Munteanu)
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Unless highly pigmented (like sunburst lichens), the lichen cortex (made of fungal cells) looks gray or greenish-gray when dry. When wet, the cortex becomes transparent, allowing the algal layer to show through with bright green or olive colours, which enhances photosynthesis under better conditions of moisture.
The secondary metabolite pigments produced by the fungus serve a myriad of functions. Aside from making lichens wonderfully colourful, they help deter foraging by herbivores such as moluscs; they are allelopathic, helping against competitors; they help weather rock; and they act as sunscreen. You could say that the fungal layer serves as a ‘greenhouse’ for the photosynthesizing algal layer.
So far, I’ve identified eight lichen species, ranging from crustose (crust-like) to foliose (leaf-like) forms. Here are my maple tree lichen:
Hooded Sunburst Lichen (Xanthoria fallax)
Deep orange Xanthoria fallax displays soralia and deeper orange apothecia disks, red maple, ON (photo by Nina Munteanu)
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This deep orange-yellow lichen attracted my attention first. Like a clarion call, each large rosette seemed to scream at me: I’m so bright like the sun! Look at me! So, I did. The lobes of Xanthoria fallax were flat to convex and raised along the margins between the upper and lower cortices where crescent-shaped bird’s nest-like soralia (chambers carrying powdery soredia) carried greenish-yellow powdery soredia (asexual reproductive structures).
In the dry this foliose lichen formed orange-yellow rosettes all over the maple’s trunk and rough bark, dominating the tree trunk and branches with splashes of colour. When wet, the lobes of Xanthoria fallax turned greenish; but the powdery soredia on the edges formed a bright contrast with their startling yellow colour. Several colonies had lecanorine apothecia (sexual disk-like fruiting bodies) with the orange disk considerably darker than the thallus.
Various colour displays of Xanthoria fallax from deep orange in dry (A) conditions to yellow-green in ever wetter conditions to deep green in wettest (E) conditions; soralia with yellow powdery soredia form wonderful contrast, red maple, ON (photos by Nina Munteanu)
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All sunburst lichens contain the anthraquinone pigment parietin, which gives them their stunning orange-yellow colour, and helps them absorb UV-B radiation. According to some researchers, this gives sunburst lichens a competitive advantage over other lichens as the ozone hole grows (which it is). Walewski also relates the space journey of its sister lichen, Xanthoria elegans: after exposure to the perils of space for two weeks, this lichen when returned to its normal habitat continued to photosynthesize and grow!
Bright orange rosette of Xanthoria fallax cozies up to ‘hairy’ Physcia adsendens on red maple tree in dry conditions, ON (photo by Nina Munteanu)
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Nitrogen is a limiting factor for most sunburst lichen that get their needs from the air. I’m told that these orange lichens become more prevalent next to farmland where fertilizers are applied. Nitrogenous compounds may also drip from tree bark or other lichens during a rain. This is most certainly why this colourful lichen seemed more concentrated on the older trunk and old bark of the maple tree over its younger, smoother branches. Walewski explains that as a tree matures, its bark softens, cracks and forms furrows that ooze alkaline nitrogenous compounds.
Xanthoria fallax colonizes trees and wood, usually in exposed environments, and is common in parks and urban environments. Ways of Enlichenment reports Xanthoria fallax colonizing the bark of oak, aspen, pine, and paper birch trees. Others have reported it growing in Norway on various sun-exposed broadleaved trees such as maple, elm, beech, birch, ash, poplar, and basswood.
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Candleflame Lichen (Candelaria concolor)
Candelaria concolor forms chaotic rosettes of tiny branched lobes and dense granular soredia on red maple bark, ON (photo by Nina Munteanu)
Rosettes of Candelaria concolor with Phaeophyscia orbicularis on red maple bark in dry conditions, ON (photo by Nina Munteanu)
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Chaotic rosettes of this tiny but bright yellow (when dry) lichen were scattered everywhere on the red maple trunk and branches. At first, I thought they were tiny immature versions of the sunburst lichen, but closer examination revealed that this finely branched foliose lichen was its own species. When the sunburst lichen turned a deep orange during dry conditions, this little lichen remained bright lemon yellow. During wet conditions, both lichens demonstrated green to yellow-green thalli that were actively photosynthesizing. Yellow granular soredia are common, particularly on the lobe margins and at times so dense to obscure the lobes.
Xanthoria fallax (left) and Candelaria concolor (right) on red maple bark in dry conditions, ON (photo by Nina Munteanu)
Xanthoria fallax (top) and Candelaria concolor (bottom) on red maple in dry conditions, ON (photo by Nina Munteanu)
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iNaturalist notes that this common lichen prefers well lit aspect of the bark of maple, ash, willow and elm. They add that Candelaria concolor, also known as Lemon Lichen, is regularly found in nutrient-enriched habitats and can be an indicator of high nitrogen in the environment when found as the dominant lichen species. This diminutive lichen is quite tolerant to pollution, found in many urban environments. Walewski tells us that Candelaria concolor likes to grow along rain tracks on tree trunks.
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Hooded Rosette Lichen (Physcia adscendens)
Physci adscendens drapes down the red maple cracked bark over the whitewash of Phlyctis argena under dry conditions, ON; note pale whitish hooded sorelia containing powdered soredia and long curly cilia (photo by Nina Munteanu)
Physcia adscendens showing marked hooded sorelia on raised lobes with powdery yellow-green soredia, long curly cilia at ends of lobes and tiny dark pycnidia on mottled maculate thallus, red maple bark (whitewashed with Phlyctis argena) under dry conditions, ON (photo by Nina Munteanu)
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This strange looking green-grey foliose lichen distinguished itself with ostentatious inflated pale helmet-shaped hoods (soralia that contain cream-coloured soredia) on raised lobes. Another distinguishing feature were the long white dark-tipped hairs (cilia), curly ‘whiskers’ that extended out from the tips of its lobes. When wet, Physcia adscendens took on a deeper green Mediterranean Sea colour, showing more marked white mottling (maculae) on the thallus.
Physcia adscendens rosette on red maple trunk in dry conditions (A) and same rosette in wet conditions (B), ON; both show hooded ‘helmets’ of soralia containing copious pale yellow-green powdered soredia. Wet thallus is a darker sea-green colour and shows more marked mottling by maculae (photo by Nina Munteanu)
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Walewski notes that, while other lichens increase up the trunk of a tree, Physcia adscendens decreases in abundance as one moves higher up the trunk. This may have something to do with light conditions or more likely nutrient conditions of the tree. Walewski tells us that older maple bark is softer and more absorbent with cracks that ooze alkaline, nitrogenous compounds. The British Lichen Society mentions that Physcia adscendens is very common on nutrient enriched tree bark, often forming luxuriant colonies along rain tracks on tree trunks. P. adscendens also demonstrates a saxicolous strategy by inhabiting low acid rocks rich in organic matter.
Physcia adscendens (right and lower right–note the pale ‘hoods’ or soralia) among other lichens on red maple trunk during wet conditions, ON (photo by Nina Munteanu)
Deep sea-green Physcia adscendens along with darker yellow-green Phaeophyscia orbicularis (far left) add colour to red maple bark whitewashed with Phlyctis argena during wet conditions, ON (photo by Nina Munteanu)
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Tanunchai et al. determined that P. adscendens was a generalist and often dominated the foliicolous lichen growing on the leaves and needles of 12 temperate tree species they studied. They also detected algae and cyanobaceria—potential photobionts—colonizing these surfaces, which partially explained why the lichen thrived there. The researchers acknowledged that factors including tree species, tree type, water content, pH and location help shape the diversity and community composition patterns of lichen.
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Frosted Rosette Lichen (Physcia biziana)
Physcia biziana on rough bark of red maple trunk showing brown young disks and older pruinated disks of apothecia during dry conditions; Xanthoria fallax in background, ON (photo by Nina Munteanu)
Rosette of Physcia biziana on red maple trunk during dry conditions; note the copious tiny dark pycnidia and more central pruinose apothecia, ON (photo by Nina Munteanu)
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Physcia biziana formed sprawling rosettes on the trunk and branches of the maple tree. When dry it was bluish-grey, which turned blue-green when wet. The upper surface was densely pruinose, covered with coarse white spots (maculae), and abundant pycnidia (tiny dark fruiting bodies). Apothecia (disk-like fruiting bodies) were common, often clustered at the centre, and dark brown, particularly the smaller younger ones; most of the disks looked bluish because they were covered in dense pruina (whitish dust or bloom). Pale rhizines darkened at the tips.
Three views of Physcia biziana on red maple under wet conditions; note the reproductive structures, disk-shaped apothecia and tiny dark pycnidia, and marked white mottling (maculae) on the lobed thallus, ON (photos by Nina Munteanu)
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Physcia biziana grows on a wide variety of deciduous tree bark and large branches in open locations. Lichens Maritimes recorded it on the dead wood of Juniper and on the bark of Pine. Ways of Enlichenment recorded it on Oak, Juniper, and Eastern Cottonwood. They also found it growing saxicolously on granite.
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Mealy Shadow Lichen (Phaeophyscia orbicularis)
Olive green Phaeophycia orbicularis, showing rhizines at lobe edges and dark mealy soralia at centre of rosette during wet conditions of red maple tree, ON; note greenish thalli of Candelaria concolor (bright yellow when dry) often associated with this lichen (photo by Nina Munteanu)
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This sprawling foliose bluish charcoal grey lichen (when dry) seemed concentrated on the trunk of the maple tree. The crustose part of the lichen was gnarly and charcoal gray, almost black and again blending in with the dry colour of charred wood, with only the leading lobes the colour of dry wood, a non-descript bluish grey. When it was wet, the lichen looked olive green like the wood itself.
When I first encountered this lichen on the nearby fence post on a wet day and concentrated on the top exposed part of the post, I thought it was just part of the wood. The leading edges of the crustose jumble were long divided slightly convex lobes with black undersides and darker edges with dark rhizines, visible at the leading margins. These extended out from large masses of dense creamy-greenish soralia (hence the term ‘mealy’), often speckled with bright green from the algal partner.
A. Darker green Phaeophyscia orbicularis (left) next to pale blue-green Physcia biziana (right) with apothecia and marked mottling; B. Phaeophyscia orbicularis surrounds Physcia biziana (with many small dark pycnidia) at centre on wet red maple bark; note the dark mealy soredia and brown-disked apothecia (right and left) on the shadow lichen, ON (photos by Nina Munteanu)
Two views of densely apotheciated Phaeophyscia orbicularis in wet conditions on red maple bark, ON (photos by Nina Munteanu)
Phaeophyscia orbicularis on red maple bark under dry conditions, ON (photo by Nina Munteanu)
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Dorset Nature notes that this lichen commonly grows on nutrient-rich bark, twigs, stones and concrete and roads. Lichenologist E. Troy McMullin notes that P. orbicularis grows on a wide variety of trees and is a known suburban and urban dweller. Based on the substrates it has been found, this highly adaptive lichen is corticolous, lignicolous, and saxicolous.
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Mealy Rosette Lichen (Physcia millegrana)
Physcia millegrana (lower right), showing frills of granular soredia, with Xanthoria fallax at upper left on red maple during dry conditions, ON (photo by Nina Munteanu)
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I found a few scattered small patches of this frilly blue-grey foliose lichen on the main trunk of the maple tree, often adjacent to Xanthoria fallax. When dry, Physcia millegrana has a pale gray thallus, spotted with white maculae. Its lobes are thin, highly dissected with margins thick with granular soredia. Apothecia (sexual reproductive structures) are also frequent, with lecanorine margins and dark brown-bluish pruinose disks. This highly successful lichen uses both sexual (apothecia) and asexual (pycnidia and soredia) reproductive strategies.
P. millegrana is a pioneer species, frequently the first to colonize stems and branches of young woody plants. Its preferred habitat is exposed bark in a forest or human altered habitat. P. millegrana is a very common lichen, often dominating urban settings and described as the most pollution-tolerant macrolichen in eastern North America. Ways of Enlichenment report finding it on various deciduous trees including the American Sycamore, and even exposed rock. While I found it only sparsely on the mature bark of the red maple, it was far more abundant on on the pine fence post I was studying down the street, growing as a lignicolous lichen. It may be more abundant on the higher younger branches of the maple, but I’m only so tall.
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Brown-Eyed Rim Lichen (Lecanora allophana)
Lecanora allophana at bottom left of photo with Physcia biziana above, showing dark pycnidia, red maple under dry conditions, ON (photo by Nina Munteanu)
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I found a few small patches of Lecanora allophana on the main trunk. All I could make out were the large ‘brown eyes’: the apothecia with distinct red-brown disks rimmed by pale grayish epruinose margins. Not surprisingly, this lichen is known to reproduce mainly sexually (through spore dispersal in its apothecia).
The Consortium of Lichen Herbaria notes that this temperate region lichen colonizes the bark and wood of both deciduous and coniferous trees. Ways of Enlichenment records it colonizing the trunk of alder and willow in BC, and poplar in Alberta. Italic 8.0 noted that this lichen was found on deciduous trees with base-rich bark, particularly walnut, maple, and ash. Sharnoffphotos recorded it on pine bark in California and trembling aspen bark in Ontario and Alaska. I also found it growing as a lignicolous lichen on the pine fence post I was studying down the street.
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Whitewash Lichen (Phlyctis argena)
Lower main branch of red maple showing dull white paint-like wash of Phlyctis argena. Note the profusion of other foliose green-gray and yellow lichen on the rougher main trunk behind, ON (photo by Nina Munteanu)
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Whitewash Lichen is well-named for resembling a dull white wash of paint. This crustose lichen formed large patches throughout the younger trunk and branches of the tree where the bark was smoother. At first, I mistook Phlyctis argena for the actual bark of the tree branches, these being concentrated on the smaller branches of the tree, much like a poplar tree will show smooth bark in its younger trunk and branches. But with closer inspection, I knew it was some kind of thin crustose lichen.
Phlyctis argena covers upper branches of red maple like white paint, ON (photo by Nina Munteanu)
Phlyctis argena covers red maple bark in a dull flat white wash under wet conditions, ON; Physcia adscendens on lower left corner of photo (photo by Nina Munteanu)
Close up of Phlyctis argena, showing bark cracks of red maple tree under wet conditions, ON; very green thalli of Physcia adscendens on lower left corner (photo by Nina Munteanu)
This generalist epiphyte grows on the bark of many deciduous trees and is reported particularly on willow, ash, oak, and red maple, even cedar. Phlyctis argena is known as being acidophyllic and tolerant of air pollution. This lichen neither harms nor benefits the tree.
Flat white Phlyctis argena on lower branch of red maple during wet conditions; other lichen include mostly Physcia asdendens (vivid sea green), Xanthoria fallax (yellow-green), and Phaeophyscia orbicularis (olive green to black), ON (photo by Nina Munteanu)
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References:
Rosette of Physcia biziana on gnarly bark of red maple trunk during dry conditions, ON. Large disk-like apothecia show abundantly (photo by Nina Munteanu)
Brodo, I. M. 2001. “Lichens of North America”. Yale University Press, New Haven, Conn.
Brodo, I. M. 2016. “Keys to lichens of North America: revised and expanded”. Yale University Press, New Haven, Conn.
De Vera, J.O., G. Horneck, P. Rettberg. 2002. “The potential of the lichen symbiosis to cope with extreme conditions of outer space—1. Influence of UV radiation and space vacuum on the vitality of lichen symbiosis.” International Journal of Astrobiology 1(4): 285-293.
Gilbert, O., 2000. “Lichens.” Harper Collins, London.
Hale, Mason E. 1967. “The Biology of Lichens.” Edward Arnold Ltd., London. 176pp.
Hawksworth, David L. and Francis Rose. 1977. “Lichens as Pollution Monitors” Edward Arnold Ltd., London. 60pp
Liška, Jiří; Herben, Tomáš. 2008. “Long-term changes of epiphytic lichen species composition over landscape gradients: an 18 year time series”. The Lichenologist. 40(5): 437-448
McCune, B. 2000. “Lichen communities as indicators of forest health.” The Bryologist 103(2): 353-356.
McMullin, R. Troy. 2023. “Lichens: The Macrolichens of Ontario and the Great Lakes Region of the United States.” Firefly Books Ltd., Richmond Hill, ON. 607pp.
Perlmutter, G.B. 2010. Bioassessing air pollution effects with epiphytic lichens in Raleigh, North Carolina, U.S.A. The Bryologist 113(1): 39-50.
Tanunchai, Benjawan, et.al. 2022. “More than you can see: Unraveling the ecology and biodiversity of lichenized fungi associated with leaves and needles of 12 temperate tree species using high-throughput sequencing.” Front Microbiol. 16(13):1-17.
Tumur, A. 2006. “Biomass of arboreal lichens and its vertical distribution in coniferous forest in western Tianshan”. Proceedings of the China Association for Science and Technology. 2: 741–744.
Walewski, Joe. 2007. “Lichens of the North Woods.” Kollath & Stensaas Publishing, Duluth, MN. 152pp.
Physcia biziana rosette on gnarly red maple trunk, showing apothecia disks and small dark pycnidia during dry conditions, ON (photo by Nina Munteanu)
Several foliose lichen colonize red maple trunk, showing their wet forms: Physcia adscendens with prominent whitish ‘hoods’; Xanthoria fallax with bright yellow or green thalli with yellow soredia; Candelaria concolor with smaller greenish-yellow thalli; Physcia biziana with apothecia disks at centre of its rosette; and Phaeophycia orbicularis with dark olive green thalli and darker powdery soredia, ON (photo by Nina Munteanu)
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Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit www.ninamunteanu.ca for the latest on her books. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press(Vancouver) was selected by Margaret Atwood in the New York Times ‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” was released by Inanna Publications (Toronto) in June 2020.
