About Lichen

Chewing Gum Lichen (Lecanora muralis)
Chewing Gum Lichen (Lecanora muralis)

Next time you are out on your travels in the country, or even in the park, garden or city, take a closer look at the trees, shrubs, rocks, walls and paving, and you will see it is alive with a matt or a spot of lichen, which comes in many different forms and colours.  So what is lichen? Well, it is usually two organisms living in perfect harmony. One is a mycobiont, the fungal partner of the relationship, and the other is  a photobiont, the photosynthetic partner which contains chlorophyll, which can be a green alga or a cyanobactarium.

Tube Lichen (Hypogymnia physodes)
Tube Lichen (Hypogymnia physodes)

The names we give lichens is with reference to the fungal partner as every lichen has a unique fungus. The combination of this unique symbiont arrangement between fungus and algae and/or cyanobacteria form the distinct body of the lichen called the thallus. Yet some lichenologists believe that the fungus is actually a parasite, and biologically changes and use the alga or cyanobacterium to obtain nutrients it cannot source elsewhere to sustain itself. Either way, this relationship, symbiont or parasitic, has enabled both parties to survive in many diverse habitats, the fungi gaining essential carbohydrates from the alga or cyanobacterium, and in return the alga or cyanobacterium is protected by the fungus by helping to keep it moist and from solar damage. To complicate matters, and what can be somewhat of an enigma, the same fungal element maybe present within the alga or cyanobaterium, and may take on completely different forms of lichen which are called photomorphs. Also, some lichens have both algae and cyanobacteria, and also may change these around using other photobionts during the different stages of the lichen’s life cycle.

Golden Shield Lichen (Xanthoria parietina)
Golden Shield Lichen (Xanthoria parietina)

The lichen body is normally made up of mostly fungi, the photobiont is usually only about 20% or less. The different forms of lichen range from foliose, which are leafy forms, crustose, which are powdery or crust-like structures, fruiticose, are like tiny shrubs or tufted vegetation, and squamulose, which are like scales or plates.  Within the body the lichen produces fruting bodies which aid in reproduction. Like other non-licenised fungi, these structures contain spores which are released into the environment.

Various lichens on canal coping stone
Several species of lichen on old canal coping stone

Lichens are very resilient organisms, and they live in extreme habitats other species could simply not tolerate or survive in. They can also survive on our industrial waste pollutants, and can be good biometers for the environment. As important elements within the ecosystem, lichens provide a good food source for invertebrates and vertebrates. Yet some lichens don’t survive the chemical attack of toxins we humans release into the environment, finding it difficult or impossible to exist, and even if they do they can carry these toxins with them through the food chain. So next time you are out and about, take a look around and spare a thought for these most beautiful, enigmatic, and important treasures of our world, and consider that these were amongst the very first living things to emerge from the primordial soup and which allowed others to colonise the land.

Lichen encrusted trees
Lichen encrusted trees

Please note that lichen identification is not easy through visuals alone, and to definitively identify some of the similar species specifically would need a microscope and chemical testing. I have identified the species gathered here mainly via morphology and the substrate they were found on, and the environmental conditions. On some tricky species I have spent many hours studying various reference material to ensure the most accurate identification, but please be aware that errors still may creep in,  and if so please let me know via my contact page.

6 thoughts on “About Lichen

    1. Thank you, Victor. It must have been a wonderful experience with the workshop. I have always been fascinated by lichens, which we can pass by without even noticing they are there. They are a world of their own.

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