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What is Lichen:

Map Lichen:

What Is Lichen:

I was driven by the question, What is Lichen, to research this amazing organism. The more I read the more intrigued I became. This is a freaky relationship between two separate classifications of organisms that bond and form a symbiotic relationship that works across most surfaces of the world.

A Great Macro-photography hub on Lichen By Homesteadbound:

Crustose Lichens:


What Is Lichen:

Lichen is a type of fungus and is not a plant at all. Lichen is also a relationship that exists both on a chemical level and on a biological level. Lichen is a family of fungus that are certainly complex and yet simple organisms. We have all seen lichen though we may not have known what it is. Many people refer to lichen as moss and that is not a correct analogy. Moss is part of the plant kingdom while lichen belongs to the fungus family which are not plants.

Lichen is a type of fungus but not quite in the same sense that a mushroom is a fungi. The difference is slight but lichen are symbiotic where other funa are parasitic. I would say that the best way to define lichen is by its relationships. This is an organism that develops a symbiotic relationship with another plant that is capable of a photosynthetic reaction. The second plant is usually a form of green algae, though not always. The symbiotic relationship between lichen and its host cell is something right out of the depths pf sci-fi.

Lichen on Tree Branch:


The Crux of Symbiosis:

The family of fungus/fungi are not capable of producing chlorophyll and as such can not create their own food source. An even more pronounced differentiation between fungi and plants is that a fungus does not have vascular structures with in its tissue. Plants use veins to transport water and nutrients from the roots to the cellular structures within the plant. Fungi have flesh that is sponge like. They absorb food from the air and from absorption. This is why lichen fungus forms a symbiotic relationship with an algae cell. The fungus receive photosynthesis from the algae and the algae receives the benefit of an extended environment. Algae are quite remarkable on their own. They are capable of living in salt water or freshwater but when combined with a lichen they can survive almost anywhere here on earth. Lichen live in the hardest regions of the earth. Their habitat range from the polar tundra to the hottest desert. They are often the first form of life in any sterile environment. Because of the symbiotic relationship they share with algae, they can live on or in environments that have no standard substance, such as, cement walls, tombstones, or icy tundra.

There are arguments that the relationship between lichen and algae is not purely symbiotic. This is primarily because humans associate these types of relationships with free will. In nature, free will has not yet been defined. Does the algae choose this relationship or it is just part of the natural order of things? For the sake of argument, I think it can be assumed that the lichen chooses this type of relationship by mechanism of survival. The lichen certainly does not fatally harm the algae and the two live together quiet peacefully. The algae reproduces as pure algae and then is absorbed by a lichen and thus the lichen is able to grow.

Crustose Lichen on A Black Walnut Tree Trunk:


The Biology of Lichen:

To begin a discussion on lichen biology requires that we first look at the general biology of plants and the differences between lichen and plants. Structurally, plants are more like humans then are lichen. Though even that statement is a stretch of the imagination, there is still truth in those words. Humans consumer food as a means of producing energy. That food is broken down and then distributed through the human body by the circulatory systems of heart,veins and arteries. Plants use a root system as a mouth and though the root system of plants is not anything like the mouth on a human the function remains the same... an intake port for nutrients. Nutrients that plants absorb are distributed by a system of veins (xylem) to the cellular structure of the plant. Plants, unlike humans or lichen, also have the capacity to produce chlorophyll which is a form of energy that is produced in the plants cells. Plants utilize sunlight to make chlorophyll and as long as there is sunlight and water, plants can feed. Lichen have no such vascular structures and they are not capable of making chlorophyll. Their "root" system is only used for anchoring the lichen to its environment. The flesh of lichen is sponge like and does not have a waxy surface or cuticle like plants do. This is the reason behind the symbiotic relationship that lichen forms with algae cells...As a means of surviving.

The physical structure of lichen is much like a lasagna with layers of lichen fungi and algae. Together the two make up what we know as lichen. Lichen is very beautiful and amazing in its own right.

A formed lichen consists of four layers. The basal layer (E in diagram below) has a single purpose, to attach the lichen to its environment. A basal attachment may be in one of two forms. Rhizines are threads or chains of lichen cells that hold the lichen to a surface through many different contact points. A holdfast is the second type of lichen basal attachment that is is much like a pedestal or a pillar. Neither basal structure contains venous structures nor do they have any purpose other then to hold the lichen in place. The lichen cortex (A/D in Diagram below) is the outer layer of the cellular structure of the lichen thallus. A thallus is a group of cells that form sheets or strings which make up the body of fungi or alga type plants. A thallus is a simple cellular form without a higher function. For the sake of this article, the Thallus should be considers the flesh of the lichen. The cortex of a lichen is the outer layer of cells that in humans would be much like our skin or on a tree may be considered the bark. The third layer is the algae (alga) layer (B in diagram below). Most lichens utilize green algae as their host or partner. Though sometimes lichens may use a blue-green algae or even cyanobacteria. In some cases a lichen may use both the algae and the cyanobacteria. Cyanobacteria are a type (phylum) of bacteria that utilize photosynthesis to produce energy. The fourth structure of a lichen is the medulla (C in diagram below) which is what makes up the inside of a lichen structure. The medulla are cellular structures that have thin cell walls and are formed in long threads. They give the lichen a soft cottony center.

Cross Section of A Lichen:

Electron Microscope View of A Green Algae Cell

Cell Diagram of Green Algae:

I added the diagram to this cell photo.

I added the diagram to this cell photo.

Inside the Symbiotic Relationship:

Because the fungi does not produce chlorophyll and because they do not have a vascular system to move nutrients from cell to cell, the fungi that forms lichen bonds with an algae cell. The relationship is formed around the mutual cooperation and survival. It is this relationship between these two organisms that interested me the most. This is a plant (algae) and non-plant (fungus) which have bonded in order to heighten their chances of survival. Each is capable of surviving without the other; however, when bonded they form a single organism which we call Lichen.

The relationship is symbiotic because neither organism harms the other. This is quite different then parasitic relationships in which one organism feeds off the other until the hosting organism is dead or the vital resource to the parasite is consumed. A parasitic relationship is often seen when studying insects. An example would be a parasitic wasp that lays her eggs on a living caterpillar. As the eggs from the wasp hatch, the larva begin to feed on the living caterpillar until and usually after the caterpillar is dead or until the wasps mature enough to undergo a metamorphic change into an adult wasp.

In the world of all living organism there are few if any other relationships that exist between the lichen fungus cell and the green algae cell. There are of course symbiotic (of sorts) relationships that exist such as the relationship between the ant and the aphid. The difference between these two symbiotic relationships is that the ant remains an ant and the aphid remains an aphid. With lichen the two cells become one organism. The benefits and the power of this relationship is amazing and the results are an organism that is complex, but capable of surviving in every landmass on earth. To make this statement clearer... If one earthly organism could colonize the moon it would be lichen. Yes that is a big if... but considering all of the other organisms including man, that answer would be none! This is the power behind Lichen.

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An Unknown Lichen Exhibiting Color:

The Three Main Types Of Lichen:

The lichen family consists of three main types of lichen. Within those "types" are a great many morphed species. The morphing occurs when more then one kind of algae is used as a host. Environmental elements can also cause lichen to morph.

The first type of lichen is called Foliose Lichen. This is best identified as a lichen that has two very discernible sides or a top and a bottom. The Foliose Lichen may have many characteristics and physical attributes such as curly lettuce type foliage. Foliose Lichen can also be flat or it can be very textured with a surface that is made up of ridges and bumps

The second type of lichen is called Fruiticose Lichen. These are more of the long hairy type lichens such as Old Man's Beard. Old Man's Beard looks much like spanish moss but moss and lichen are not even closely related. Some Fruiticose Lichen also have cups and look like small fungus.

The third type of lichen is called Crustose Lichen, and is much as the name describes, It forms a type of crust. These lichen like to cover a surface. These are most likely the lichen you would see on old rocks and newer stone walls. They can be very brightly hued and can be quite beautiful to look at both from afar and up close.

Foliose Lichen:

Old Man's Beard Fruticose Lichen:

Crustose Lichen:

Lichen are Amazing:

They survive on almost every part of the earths surface including Antarctica. They live in the hottest desserts, on the highest mountains, and the coldest areas of earth. They live more places then do ants and that alone is amazing. How do they survive such diverse climates and habitats? There survival is linked directly to the unique relationship between the fungi and the algae. Both organisms give something to the relationship. The algae provides photosynthesis. The fungus provides a state of stasis that allows both organisms to survive harsh and dire environments. Because fungus do not have vascular structures they rely on moisture and wind to provide them with sustenance. The outer layer of the fungal thallus is very thick. It is capable of preserving the liquid that is found in the inner cells. As long as the algae has liquid it can continue the process of photosynthesis. If the lichen reaches a state where it is too hydrated to provide the algae with water, both organism enter a state where they merely are. This is called stasis. There they wait until water or liquid comes into contact with the fungi's thallus or outer cortex. The liquid is then absorbed and normal life continues. Lichen are able to survive such extremes because they store food and supplies in their inner cells. This enables the lichen to go long periods without water or photosynthesis.

Lichens are very beneficial because of their ability to absorb everything in their surroundings. Because of this lichens provide a great deal of information to science about the quality of an environment. They also do not thrive in areas where there is higher levels of air pollution. This makes monitoring air pollution a matter of watching lichen colonies.

Lichens are so amazing that they are often the first organism to invade a sterile environment. Because of their cooperative relationship, Lichen are able to adapt. Over a period of time lichen actually prepare an environment for other forms of life. Lichen live and die and as such build up the soil, provide nutrients, and continue the process of life for organisms that are much more fragile.

Gelatinous Lichen:

Gelatinous Lichen:

Lichen further amaze us by utilizing bacteria instead of algae as a partner. Cyanobacteria are bacteria that preform photosynthesis. The lichen funga will incorporate cyanobacteria as a partner in their symbiotic relationships. They will sometimes include both algae and cyanobacteria. The partnership with the cyanobacteria causes the lichen to be jelly like when they have absorbed water or when located in a wet environment. True to their lichen forms these gelatinous lichen will also become dry if denied water but will spring back to life when watered.

Cyanobacteria were thought to be a specialized algae but have since been moved from there classification and placed in another phylum.

Lichen Reproduction:

Lichen reproduction is bizarre. It is a form of A sexual reproduction that is similar to cell reproduction but at the same time completely different. This is because for lichen to reproduce, two organisms must share in the A-sexual reproduction. That would seem a contradiction but that is the very essence of lichen.

Lichens reproduce by Soredia which are tiny clusters of lichen fungi and algae cells that are delicately wrapped around each other. The parental lichen produces soredium through a cellular fragmentaion process. Because lichen is made up of two organisms, both organism must be present if reproduction is to occur successfully. The soredia are housed in a tubular structure that is referred to as an Isidium. The Isidium is fragile and meant to be broken off by animals or even by the wind. The lichen soredia then drift away and form another lichen colony. Lichen are only dependent upon themselves for reproduction, they do not require pollination. The fragmentation process involves both the fungal lichen and the algae. To relate this process to humans... imagine cutting off a very small piece of your finger and having it grow into another you.

Disecting Microscope view of Lichen and Soredia-Soredium




If we consider that the relationship of a lichen is a cooperative effort of two very different organisms which are fungal and a plant the other a fungus, and we know that there are aquatic fungi and aquatic algae, is it possible that lichen could be related to or even found on a salt water reef?

While most reef structure is created by cellular waste and exoskeleton shedding of animals but what about consideration to reef life such as coraline algae or red slime algae which is a cyanobacteria... Is not the possibility there?

Coral Reef:

Other Quality Lichen Hubs


Imogen French from Southwest England on November 08, 2013:

Quite fascinating, and lichen is really rather beautiful when you look close up.

jeff on July 22, 2013:

Hi all

I’m writing from BBC TV in London. We are making a film for BBC Science about the atmosphere. It involves travelling in a giant airship from Florida to California carrying out a variety of experiments along the way.

We plan on coming to Houston, Texas, where I understand there has been a remarkable improvement in air quality during the last 14 years. My understanding is that this improvement is due to a number of factors – good science, new technology and robust legislation.

We are very interested in finding an indicator species which points to this improvement in air quality (if such a thing exists). Ideally it will be a species that has made a comeback in the city due to cleaner air. Can anyone help please? Is there a type of lichen perhaps – the presence of which indicates cleaner air? Please contact me via email on

Would appreciate your advice on this …

Best wishes

Jeff Wilkinson

BBC Producer Director

BBC Science

Deborah L. Osae-Oppong from Chicago, IL on February 27, 2013:

Very cool, and very well done! :) Symbiosis is such an interesting phenomenon! I appreciate the expertise and explanations in this post! Thanks for sharing.

David Stillwell (author) from Sacramento, California on September 17, 2012:

each lichen has its own scientific name that follows the taxonomy chart used by science. Some examples of lichen are Caloplaca flavescens or Hypogymnia physodes. Notice that the second name in each example is not capitalized... that indicates species... and the capitalized name indicates family.

Tim on September 17, 2012:

What's the scientific mean for Lichen?

David Stillwell (author) from Sacramento, California on September 16, 2012:

Ea The Querier: Like the word FISH, lichen is both singlar and plural, though it is common to hear lichen made plural by adding an S to it... lichens. A large group of lichen would normally just be called lichen... though the term colony can also be applied. Many large lichen are just one organism. It would be acceptable to say There is a colony of lichens ... if you are discussing a vast amount of lichen or a group that is made up of different types of lichens. ...

Ea The Querier on September 16, 2012:

Hi Dave,

I'm new here... and I just want to ask you something???

What do you call a large group of lichens???


ea on September 16, 2012:

Hi dave!

Im a seventh grader ,and im just asking what do u call a large groups of lichen??please answer...

David Stillwell (author) from Sacramento, California on December 20, 2011:

Think of it like the pickleweed plant of the salt marsh...It also absorbs salt then then turns red. The red lichen picture was taken at the shore...

Cindy Murdoch from Texas on December 20, 2011:

That makes sense that the cyanobacteria would be red from salt, because in the marine environment it is definitely red. When I look at the similarities of a picture of the coral reef and a lichen colony, it is pretty amazing and would be easy to see lichen existing.

Thanks for the clarification.

David Stillwell (author) from Sacramento, California on December 20, 2011:

HSB: Lichen do not thrive and sometimes die if the air quality is poor. Scientist also can extract tissue from the lichen to measure air pollution... that is because lichens absorb things into them. The red slime algae is a cynobacteria but in lichen it the red coloration could be a number of things such as absorption of salt. I still think there are lichens that live under the the sea..., etc.

Cindy Murdoch from Texas on December 19, 2011:

I did not know that Old Man's Beard was a lichen. I thought it was a moss!

You said, "Because of this lichens provide a great deal of information to science about the quality of an environment." That is really cool!

Could that unusual colored lichen have some of the cyanobacteria in it to give it that color. Cyanobacteria algae in my saltwater tanks was always red - a deep wine red.

That gelatinous lichen looked like mercury!

I love the last picture of the coral reef, and it does look like lichens from that perspective. At first I thought it was. Very interesting.

I truly enjoyed this hub. It was so well researched. It was amazing.

David Stillwell (author) from Sacramento, California on December 18, 2011:

Derdriu: Thank you for reading... the relationship of lichen fascinates me a great deal. I am equally impresses by lichen's ability to live practically anywhere where is not high levels of air pollution. The coral reef and potential link to lichen also fascinates me... both are ancient!

Derdriu on December 18, 2011:

Davenmidtown, What an engrossing, informative, useful summary of what it means to be a lichen in a world of animals and plants! In particular, I like the way you use your own pretty pictures as well as illustrative photographs and scientific illustrations. You do a great job in saying what a lichen is and is not as well as in defining it by what it does and whose company it seeks and keeps. Additionally, I'm impressed how you raise our interest to the point that you end with suggestions of future areas of investigation.

Thank you for sharing, etc.,


David Stillwell (author) from Sacramento, California on December 16, 2011:

Kelsie: It makes sense to me about your observation of lichen placement. Lichen is usually spread by the wind or by animals that brush up against it. Sometimes it will spread a great distance from its parent plant or at other times a few inches. It really depends on the vector of distribution. In the case of the larger rock and the sagebrush... I would look and see if both have lichen... it is possible that the sagebrush introduced the lichen to the rock via simple gravity. That would be exciting because the lichen would have been (most likely) carried by the wind from elsewhere. Another question that intrigues me is how lichen might have reached the arctic and Antarctica. I suspect that the answer is migratory birds feet... hmmmm. It seems to me I did come across some light research on lichens use by Native Americans... I will have to see if I can remember where. I do know that lichen was often used in making dyes.

Orchids are the largest family of plants. The next largest I believe is the sunflower family. The care of Orchids is also interesting because they do not really require soil in the sense of a garden. They are often what I call an aerial that they grow on things like trees but not necessarily on the ground. They also seem to not be so much parasitic as just opportunistic by making their home in a small crook of branches that may hold moss, etc. Orchids rely on dissolved minerals in rainwater to feed themselves. Orchids for the most part at not carnivorous, though they have an extremely complicated relationship with pollinating insects and use basin like blooms to attract insects but that relationship is purely for pollination. Orchids like Lichen are fairly amazing. They are one of the most important plants on the planet and I would guess that as much as 50% of orchids have not even been discovered or labeled yet.

KelsieGriggs from Provo Utah on December 16, 2011:


I love to think so the thought that my words help you think gives me great pleasure. Thank you for being open to the "out of this world" :) ideas I might throw at you. I have noticed walking around in fields that have a variety of "rocks" that the lichen seem to have their own choice in material as well as environment. Some lichen preferred being on a large rock tucked under a sagebrush bush and yet other lichen as well as the same type of lichen preferred small pebbles in the open on top of dirt and ant mounds and such. I believe lichen do have a "free will" so to speak however my beliefs lie in that everything is moved and changed with the winds and tides as well as our moon. What does this mean? I believe it is our proof that nature's "free will" is simply a natural law that only The Mother will know and science will never be able to label simply due to not being able to open our minds to things that are not concrete. Science can label simple things however cannot identify or study many great things in this world. I feel it is our Mother's way of reminding us that she is and always will be our greatest teacher. It feels so great to know that I am not the only one to see the rarities which we are abounded with. Thank you for sharing Dave! Here's another one for you. The orchid does not qualify under any other category. It falls in it's own category and there are many categories which it is close to (such as the flytrap plant which is also a parasitic plant however the orchid (and all of the many varieties which encompass this name) has qualities that aren't parasitic but symbiotic as well. If I were to actually compare lichen to another living thing I feel it would be the orchid due to the rarities as well as other factors you discussed earlier. Also have you come across any research that includes information from our ancestors about lichen? The information I have found is very little so I am hoping someone might have a source or two to share. Thank you again Dave! Great subject!


David Stillwell (author) from Sacramento, California on December 16, 2011:

Peggy W: Thank you for the comment and the complements. I think Lichen is quite beautiful and it comes in so many different colors. It was once used to make dye.

David Stillwell (author) from Sacramento, California on December 15, 2011:

Hello livelonger: I think Lichen is amazingly capable of freewill...I have always been interested in how plants communicate... I know trees communicate using chemicals... maybe one day we can crack that code as well.

Jason Menayan from San Francisco on December 15, 2011:

Fascinating! Great photographs, too. I had only been familiar with the "standard" yellowish-green kind of lichen before; I wasn't aware that gelatinous and "beard" lichen existed. Some of the other types you describe I might have confused with something else entirely, based on their texture and color. I know that some people try to encourage its growth (for home/garden decoration) but it's apparently very difficult to encourage its growth on its own. I guess it does have a free will! Thanks for a great Hub.

David Stillwell (author) from Sacramento, California on December 15, 2011:

Kelsie: No need to apologize...I love that you make me think about things.... you are correct about the life energies... and that is one of the things that attracted me to the lichen... they have a power that nothing else I have found on earth possesses.... I see that in the intelligence of the octopus too. I see that in the inquisitiveness of a Praying Manid that will sit on my hand and study me as I study her. There is a lot more to creatures, plants, minerals and rocks, etc then we give credit for. To a degree I mean energy but not quite in the way of metaphysics...It is like walking deep into a vast forest and feeling it pressing down upon you... Please keep me thinking... I enjoy it a great deal...

KelsieGriggs from Provo Utah on December 15, 2011:

Dave, :)

I apologize for my writing leading you astray into thinking I was comparing the two. The only comparison of the two is that they are both rare species within their respective worlds. I have thought about connections such as you are speaking about however I am a generalist and have an intuitive generalistic view on the world. My mother always said I take a paragraph and write a book because i go on all of these side trips. Hmmm sort of like I am doing here. :) Okay my point is only to expand the thought of black and white thinkers. Simply put, if there are rarities within each category of animals, plants, bugs, birds, reptiles, minerals, moss, fungi, and what I consider it's own species lichen, then there is a possibility that this element in the lichen which is it's life force may have different energies associated with the life force energy that may be more advanced than other living matter which may be the same source that enhances certain properties which may bring validity to our ancestor's belief of it's healing properties. I apologize for misleading you about my views with obviously poor writing as well as my tendency to ramble such as I am continually doing here.:) Thank you for your information and for making me smile at myself. :) Thank you Dave! :)


David Stillwell (author) from Sacramento, California on December 15, 2011:

Hello Kelsie: Thank you for reading and for the great comment. I have had to ponder this a wee bit. Interesting connection between Lichen and Cephalapods. The pedestal foot is certainly a clue. Where I lose faith in the argument is in the difference in flesh between the two orders. I suppose an argument could be made that evolutionary forces could cause the differentiation between muscular flesh and the Lichen Thallus due specifically to the methods by which each organism collects food. Further differences could be attributed to the vast environmental difference experienced by both sets of creatures. One of the keys to this argument would be the common snail which has members of their family in both environments and yet the differences between land and water snails is usually slight... especially if one were to compare the turbo snail and the mystery snail to the common garden snail. Each have a basil foot, each are capable of A sexual reproduction, and each can live on land or in water for a short period of time... the difference in adaptation to a marine environment or freshwater environment not withstanding) ... And though snails are gastropods they are still mollusk. Snails also have an odd way of preserving themselves during extreme droughts and reappearing after the rains. There could be a connection if we looked deep enough and that is probably our greatest weakness.... how much of what is written is based on assumption due to the fact that did not have the technology at the time to prove something one way or the other. While I see the potential of a relationship between the two, at this point I would have to say maybe not so much.... find the link to lichen and symbiotic corals and the bridge to making your argument would be stronger.

KelsieGriggs from Provo Utah on December 15, 2011:


Thank you for the exceptional scientific information about lichen. I love lichen and have a great deal of respect for it. Amazing how air polution affects nature a great deal yet we have "standards" that tell us when we are safe or not.:) I want to add that lichen are actually considered to be in their own class of order. It is neither moss or fungi due to a compound it contains that is not found in any other species of plant, moss, or fungi. It was thought by our ancestors to be very powerful due to this compound which they of course were unable to identify however they saw the energies in the lichen and used lichen regularly in many medicinal preparations as well as spiritually. And I wanted to hear your thoughts about this: I feel lichen are the cephalapods of the land environment. If you think about this, there are only three cephalapods with variations of each, octopus, squid, and the cuttlefish. Cephalapods are classified due to their having a "headfoot" which is their basal foot that is their "mouth" so to say. The world is full of variations and such. Science has only been able to go so far as to classifying organisms however Mother Nature has thrown in a few surprises here and there which are unexplainable to keep us on our toes. The life force energy that science can't figure out is what drives us all. I thrive on the knowledge that our world is full of secrets and also full of wisdom at the same time. I enjoy learning about what Mother Nature has given us to figure out. She is and always will be our greatest teacher. To find the answers look to her and she will provide. Thank you for sharing this great information. I hope this drives many to the wonders that abound us. Thank you Dave! :)


Peggy Woods from Houston, Texas on December 14, 2011:

Very interesting hub regarding lichen. I always admire it when discovered on trees and elsewhere. It can be quite beautiful. Voted up, useful and interesting.

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