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All About Lichens

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Lichenologists are scientists that study lichens.  They can spend hours studying the living crust of a rock. 

So what are lichens?  They are, in fact, two organisms that are living and working together.  If you read about mushrooms (fungi), you learned about "hyphae" or fungal filaments which are strands of the fungi that form a mesh as they grow.  Living among the filaments are algal cells.  About one-quarter of all known fungi, world-wide, are lichenized.  According to the Association for Lichenology, a lichen is "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure".

The dominant partner is the fungus from which the lichen gets the majority of its characteristics.  Alga may be green or a blue-green alga, otherwise known as cyanobacteria.  Many lichens have both types of algae.  While lichens are fibrous and stiff, non-lichenized fungi are usually soft, fleshy and delicate.  

Note for students regarding spelling: "alga" is the singular form; "algae" is plural.  Pronounced:  "al-jee".

Some lichen types can provide a glimpse into a region's air quality and pollution levels.  Have you noticed that there are few lichens in large cities, but many in the countryside?  Lichens have the ability to absorb everything in their atmosphere.  Scientists can extract absorbed toxins such as heavy metals to measure levels present in our atmosphere.  

You can read more from the USDA Forest Service National Lichens and Air Quality Database and Clearinghouse how this is done.  (Note, this link will take you outside the FreeTiiuPix. website.)


Did you know....

- lichens can be found in many colours and sizes;

- while lichens have properties similar to plants, they are not plants;

- lichens can be found almost everywhere, even in extremely dry environments;

- there are 13,500 to 18,00 known species;

- a "macrolichen" is one that is leafy or bush-like;

- all other lichens are called "microlichens";  Note:  "macro" and "micro" do NOT refer to size!

- while many lichen names include the word "moss", they are NOT related to mosses or other plants;

- lichens do not have roots with which to absorb water or nutrients;

- a lichen can absorb 3 - 35 times its weight in water getting its moisture from the rain, dew and fog;

- lichens can be found growing on rocks, walls, tombstones, roofs, soil, or other plants;

- some lichens live for a very long time!  

- lichen growth may be used to judge air pollution in a region.


Lichens have various types of growth formations



Fruticose (shrubby) lichen grow in a three-dimensional fashion.  They may grow like little shrubs upward, or hang down in strands.  It is often difficult to tell which is the upper and which is the lower surface.  These lichens look shrubby and can be removed from their surface by hand. Examples of genera:  Alectoria, Bryoria, Letharia, Ramalina, and Usnea.


Foliose (leafy) lichen look like they have leaf-like, two- dimensional, parallel flat layers made up of lobes.  This type of lichen are attached by root-like threads and can be easily removed with a knife.  Examples of genera:  Hypogymnia, Lobaria Parmelia, Peltigera, Physcia, Platismatia, Rhizoplaca and Umbilicaria.


Crustose (crusty)  lichen look like they have formed a crust over rocks, trees, or walkways.  These lichen cannot be removed from their surface without them crumbling away.  Examples of genra:  Graphis, Lecanora, Lecidea, Lepraria, Ochrolechia, Pertusaria and Rhizocarpon.


Squamulose lichen are somewhere between foliose and crustose which are scale-like.  They are composed of small "foliose" thalli but are much smaller - they look like little lichen "flakes" growing in colonies.  Examples of genera:  Cladonia, Hypocyenomyces, Pannaria, Psora and Stereocaulon.



*** Warning ***

Although there aren't many lichen that are poisonous, there are some that are high in vulpinic or usnic acid and they are toxic.  

While I have tried to link images with lichen names, I am not a specialist in this field.  I have used books and images to try to look up, categorize and name the various species.  My identification should in no way be relied upon as accurate. YOU alone are responsible for properly identifying any lichen that you may be interested in.  I have attached names to images which I merely THINK resemble the species.

I am grateful for corrections to taxonomic determinations, please contact me at FreeTiiuPix 


Did you know....

that other than fruticose lichens, the others grow very slowly, about .5 to 5 mm each year?  Measurements are taken as to how much their circles have expanded.

Fruticose lichens grow quickly, up to 2 cm each year.  

The term "lichen" is derived from the Greek word "leichein" which means "to lick" - most likely in reference to the tongue-like structure of many lichens.


Unidentified Lichen Species


Lichens on granite rocks iin northern Ontario.

Lichen - 8
Various lichen growing on granite rock of Canadian Shield near Parry Sound, Ontario.

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Lichen - 9
Various lichen growing on granite rock of Canadian Shield near Parry Sound, Ontario.

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Did you know....

that lichens grow on every continent?  Different species can survive in all climates and at all altitudes.  They need an undisturbed surface, time and clean air in order to grow.


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Lovely Lichens &
Magnificent Mosses








Lichens - Two types of organisms living together - a fungus and an alga.  The fungus makes the body that protects the alga, and the alga provides the food for the fungus.




















Thoreau once wrote:  "I find myself inspecting little granules as it were on the bark of trees - little shields or apothecia springing from a thallus - such is the mood of my mind - and I call it studying.











Classification - 

Lichens were problematic for biological classification but are now classified as fungi under the genus and species of the host fungus.











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