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LICHENS

… are living organisms familiar to everyone but known by no one.

Lichens spread globally through spores carried by air, establishing new habitats far from their origins. Once spores reach a suitable environment, they grow into new lichens if they find the right algal partners.

Lichens represent a philosophical enigma, existing in a liminal space that defies simple categorization—they are neither completely plants, nor algae, nor strictly inanimate. Their presence on stones and trees speaks to a profound adaptability and a unique evolutionary history that challenges human understanding. As life forms that cross boundaries, lichens provoke us to rethink life and survival, illustrating a world where mutualistic relationships are essential but often misunderstood.

Six months ago, I ventured into a fascinating micro-universe, seemingly plucked from Miyazaki’s anime, with a curiosity revived from childhood. After receiving a magnifying glass to observe these communities on the walls of historic buildings in Amsterdam, I was invited by Adriana Knouf (tranxxeno lab) to write them a letter. Suddenly, something changed in my relationship with lichens. Their story inspired me. I now carry a small magnifying glass and a UV flashlight to discover them in nature. So far, I’ve encountered 14 species.

Lichenologists estimate that there are between 13,500 and 30,000 species worldwide. Approximately 6-8% of the Earth’s surface is covered by lichens, described as “autonomous miniature ecosystems” and “bioindicators for air quality” or “being singular plural”.

Lichens live at the boundary between species and ecosystems, embodying questions about adaptation, resilience, and interdependence. These mutualistic entities can survive in extreme environments, from polar regions to space, where they demonstrate remarkable resistance to radiation and temperatures. Their varied forms and colors reflect an impressive diversity that challenges conventional classifications.

Symbiosis describes the intimate, mutualistic relationship between species that enhances survival. Lichens—a partnership between algae, cyanobacteria, and fungi—offer mutual benefits, such as photosynthesis and nutrient absorption.

I. LICHENS

The lichen species presented were carefully collected from Romania, Greece, Austria, Hungary, Germany, France, and Spain with the help of passionate and curious friends, to whom I extend my thanks: Monica, Nicoleta, Bogdan, Philip, Crișan, Tudor, and Alina.

The identifications provided below are approximately 80% accurate, as lichenology is still an evolving field with many known and unknown species yet to be fully explored or classified, reflecting both the complexity of lichens and the limitations of visual identification without more detailed analysis.

1. Xanthoria parietina

• the “common orange lichen” or “yellow wall lichen”. This species is characterized by its vibrant yellow to orange coloration, with flattened, cup-like structures known as apothecia, which are reproductive structures.

Xanthoria parietina is often found in nutrient-rich, sunny environments, such as rocks, walls, and tree trunks. It is a common species, widely distributed, and is often used as an indicator of air quality. (Xanthoria found in: Romania, Hungary, Germany and Austria)

The partners that form this species of lichens are:

1. Fungus (Mycobiont):  – provides the structural framework and physical protection to the algae or cyanobacteria and creates a stable environment for the photosynthetic partner by absorbing water and nutrients from the air and substrate (e.g., rocks, trees). The fungus forms most of the visible body of the lichen (the thallus), which helps the community survive in harsh environments like rock surfaces or tree bark.

2. Algae and/or Cyanobacteria (Photobiont):- Photosynthesize and produce carbohydrates (sugars) through photosynthesis, which they share with the fungus. The algae or cyanobacterium supplies food, allowing the fungus to survive in environments where it would normally not be able to thrive alone.

2. Peltigera

• commonly known as “dog lichen”. This genus is known for its large, leafy, and sometimes lobed thalli with a distinctive fuzzy or hairy appearance along the edges.

“Peltigera” species are typically found in moist, shaded environments, often on soil, moss, or rotting wood. In Romania, where I found this specimen, it would likely be in a forested area, possibly near streams or in damp places.

Ecological Role:

1. Nitrogen Fixation: Some species of Peltigera have cyanobacteria as their photobiont partner (instead of green algae), which allows them to fix atmospheric nitrogen into a form usable by plants. This means they play an important role in adding nitrogen to the ecosystems they inhabit, especially in nutrient-poor environments.

2. Soil Formation: Like many other lichens, Peltigera species contribute to the breakdown of organic material and the creation of soil over time. Their growth on decaying wood or soil helps with the decomposition process.

3. Symbiotic Structure: Like all lichens, Peltigera is a symbiotic relationship between a fungus (mycobiont) and a photosynthetic partner (photobiont). The fungal partner provides protection and structure, while the photobiont (either green algae or cyanobacteria) photosynthesizes to produce food for both organisms.

3. Evernia prunastri (oakmoss)

• This lichen species is widely distributed in Europe, including Romania, and is typically found growing on the bark of trees, especially oaks, but also on conifers and other deciduous trees.

“Evernia prunastri” has a fruticose (shrub-like) growth form with flattened, strap-like lobes. The lobes are often branched and loosely attached to the substrate, which gives it a slightly tangled or bushy appearance.

The thallus (body) of this lichen is usually pale green or greenish-white on the upper surface and lighter or white on the underside.

Evernia prunastri prefers growing in temperate forests, often in areas with good air quality, as it is sensitive to pollution, particularly sulfur dioxide. In Romania, it can be found in forests and natural areas with clean air, growing on the bark of trees in both rural and forested areas.

Fragrance Industry: This lichen is highly valued in the fragrance industry and is harvested for use in perfumes. Oakmoss is a key component in many fragrances, contributing a deep, woody, earthy scent.

4 Phaeophyscia orbicularis

This is a common foliose lichen species that grows on various substrates, including tree bark, rocks, and wood, often in urban environments like Paris, France.

Phaeophyscia is a very adaptable lichen and can be found in both rural and urban environments. It is tolerant of air pollution, which is why it can thrive in cities like Paris, where air quality may not always be ideal for more sensitive lichen species.

Lichens like *Phaeophyscia* play a role in breaking down surfaces, contributing to the formation of soil over time. They also provide microhabitats for small invertebrates and help retain moisture in their immediate environment.

5 Lecanora muralis

This species is commonly found in Mediterranean climates, such as Greece, and is recognized for its crustose (crust-like) form and distinctive apothecia.

The lichen has prominent cup-like -apothecia-(the reproductive structures), which are a hallmark feature of the genus Lecanora. It is very common in sunny, exposed areas on rocks, walls, or even man-made structures, especially in Mediterranean climates like those in Greece. It can tolerate dry conditions and grows on nutrient-poor substrates.

Pioneer Species- Lichens like Lecanora muralis are important pioneers in harsh environments. They contribute to the slow breakdown of rocks, leading to soil formation, which is vital for other plant species to eventually establish themselves.

6 Ramalina farinacea, (dust lichen or cartilage lichen)

This is a common lichen species found in Mediterranean regions, including Greece.

the species name “farinacea”meaning : “floury” or “powdery”.

Ramalina commonly grows on tree bark, rocks, and occasionally other surfaces such as wood. It prefers dry, exposed environments, which makes it well-suited to the Mediterranean climate.

Ramalina lichens have a fruticose growth form, which means they grow in a branching, bush-like structure. The branches are flattened and strap-like.

7. Physcia adscendens

This genus is commonly found in temperate and Mediterranean regions, including Greece, and is known for its foliose (leaf-like) structure.

Physcia species often reproduce vegetatively through soredia, which are powdery granules containing fungal and algal cells.

Some species of Physcia, like *Physcia adscendens*, are known for having hair-like projections (called cilia) along the margins of the lobes, though these are not clearly visible in this image.

– Physcia species are commonly found growing on tree bark, rocks, and sometimes man-made surfaces like walls. They thrive in exposed, well-lit areas, and they can tolerate a certain level of pollution, making them quite common in both urban and rural environments.

-Lichens like Physcia contribute to nutrient cycling by breaking down organic matter and helping form soil over time.

FOTO FLAVOPARMELIA

8. Flavoparmelia caperata(common greenshield lichen)

This species is widely distributed and can be found on tree bark, rocks, and sometimes man-made surfaces.( found in Spain)

The surface appears to have a rough or powdery look, possibly due to the presence of **soredia**, which are reproductive structures used for vegetative reproduction. The granular texture suggests the lichen is reproducing through soredia rather than by producing apothecia (fruiting bodies).

This lichen, like all others, is a symbiotic relationship between a fungal partner (mycobiont) and a photosynthetic partner (photobiont). The fungal partner provides the structure, while the photobiont (green algae) produces sugars through photosynthesis.

9. Aspicilia or Lecanora

which are common in Mediterranean climates and can be found on rock surfaces.

This lichen has a crustose form, which means it grows closely attached to the substrate (rock or tree bark) and cannot be easily separated from it. The surface appears rough and somewhat granular, which is typical of crustose lichens.

germania

FOTO CLADONIA

10. Cladonia rangiferina ( reindeer lichen).

While this genus is most commonly associated with boreal forests and tundra, some species can be found in temperate forests, including Germany.

Cladonia species are often found in nutrient-poor soils, on rocks, or on decaying wood. In forest ecosystems, they grow on the forest floor or on tree trunks and thrive in open, well-lit areas with little pollution.

Like all lichens, this species is a symbiotic organism as well.

Some species of Cladonia are important food sources for animals like reindeer and other herbivores in northern climates. Even in temperate forests, lichens serve as a habitat for small insects and microorganisms.

11.Verrucaria

Verrucaria species are often found growing tightly attached to rock surfaces and are common in temperate regions like Austria. 

The lichen has a tightly adhered, crust-like appearance, growing directly on the rock surface. This is typical of crustose lichens, which form a thin, continuous crust that is difficult to separate from the substrate.

The reproductive structures (perithecia) often appear as small black dots or slightly raised bumps. These structures produce spores that help the lichen propagate. The dark spots visible in the image could be these perithecia.

Verrucaria lichens contribute to the weathering of rocks over time by secreting acids that slowly break down the substrate. This process plays a role in soil formation and nutrient cycling in ecosystems.

Crustose lichens, especially those in the Verrucaria genus, can also serve as bioindicators of environmental conditions, particularly air quality and water flow in their habitats.

12. Parmotrema perlatum (pearly shield lichen)

This genus is characterized by its foliose (leaf-like) growth form, lobed structure, and often a distinctive texture.(found in Austria)

The lichen has a foliose growth form, with large, flat lobes that are loosely attached to the substrate. The lobes have a wavy appearance, which is typical of Parmotrema species.

The thallus (body) is light gray to bluish-gray in color, with a slightly powdery or cracked surface texture, as seen in the image. This is common in Parmotrema species.

No Apothecia Visible: In this image, no apothecia (fruiting bodies) are visible, but *Parmotrema perlatum* is known to produce black apothecia along the edges of its lobes when it does reproduce sexually.

Parmotrema species are sensitive to air pollution, especially sulfur dioxide, and their presence is often an indicator of good air quality.

As with other lichens, Parmotrema species are symbiotic, consisting of a fungal partner (mycobiont) and a photosynthetic partner, typically green algae (photobiont). The fungus provides structure, while the algae perform photosynthesis to produce nutrients.

### Conclusion:

II. Bracket fungus

• (also known as shelf fungus), bracket fungi are part of the Basidiomycota phylum and grow on trees or wood, often indicating a wood decay fungus. They are essential decomposers in forest ecosystems.

•    – Bracket fungi play a critical role in breaking down lignin and cellulose, two complex components of wood. By doing so, they help decompose dead trees and organic matter, turning them into simpler compounds that enrich the soil.   – This process recycles nutrients back into the ecosystem, benefiting plants and other organisms that depend on nutrient-rich soil

•   – As fungi break down dead wood, they help create habitat for various organisms, including insects, birds, and small mammals. Decomposing wood can become a home for a variety of species, contributing to biodiversity.

•  – While many bracket fungi are saprotrophic (feeding on dead wood), some species can form mutualistic relationships with living trees, aiding in nutrient exchange.

•   – Like most fungi, bracket fungi are composed of hyphae, which are long filamentous cells. These hyphae grow together to form a network called a mycelium, which penetrates the wood and secretes enzymes that break down organic material and Fruiting Body:   – The visible part of the bracket fungus, often called the conk or bracket, is the reproductive structure of the fungus. This part produces spores that are released into the air to propagate the fungus.

• Without fungi, forests would accumulate dead wood, and the nutrient cycle would be much slower.

Lichens embody deep ecological wisdom, emphasizing the interconnected nature of existence.

They challenge rigid life classifications and hold significant cultural value in many indigenous communities for their medicinal and ritual uses. The study of lichens, or ethnolichenology, explores human-lichen interactions, highlighting the integral connection between humans, non-humans, and the broader environment. By adopting a “lichenized” consciousness, we can recognize the relational nature of life, promoting a transformative approach to environmental and social engagement.