8. Royal Park

The identification of lichens 

Below you will find the audio and text of the walk !
Have a good adventure !

To identify lichens, two criteria are important: 

  • The forms of the lichen : foliose, crustose, fruticose, leprose
    (see Stop 2, here for more info)
  • The reproduction methods (see the previous stop (7) here for more info)

Other details are important such as the colour of the lower surface of the lichen, the type of rhizines (which are the attachments that allow the lichen to hold onto the surface). The rhizines can be single or double (among others).  

The tree you are facing now is filled with a foliose lichen that we have seen a lot before. Do you remember its name ?

It’s Xanthoria parietina.

If you look at the wall behind the tree you can see the same species with many others. On the upper part of the wall there is a panel of crustose lichens. Look at the pictures below to help you recognise them.

What is an identification key?

It is a tool that allows you to identify a living species (animal or plant). The key (document) contains a series of questions that allow you to find the name of the organism in front of you, based on observable morphological features. Below is an example of some questions found in an identification key. I will refer to an identification key as ID key in this text. A full ID key that I created based on the urban lichens I found in Edinburgh and in Brussels can be found here.

How does an ID key work?

In an ID key, you read the first statement. If it matches (one of) the morphological traits you see on the organism you are trying to identify, you continue on to the next statement referred to with a number. You continue following the numbered statements until you find the name of the lichen (or other organism) you are trying to identify.

What is taxonomy ? How do you name a species ?

Taxonomy is a way of naming and recognising species. It is a similar process to naming humans with their first name and their last name. For example, your family name indicates the larger family to which you belong, and the first name represents your individuality within that family.

Remember the species we saw: Xanthoria parietina, Physcia adscendens, Physconia grisea, Candelariella aurella. In general, the first part of the name is the genus (like the family name for humans), indicating the family to which the individual under study belongs. Then, parietina, the second part of the word indicates the species. This is more unique – like your first name.

Before 1753 (in the early 18ᵉ century), plants were differentiated based on a description. For humans that would be like saying: “the person with a pointy nose”.

What’s wrong with this kind of description?

In 1753, Linnaeus started to use (Latin) names to differentiate plants… which is much easier. There are several taxonomic ranks, which are classifications ranging from broader families to the most precise (the species name).

Here is an example of the different ranks of life:

Kingdom > Division/Phylum/Branch > Class > Order > Family > Genus > Species

Classification ranks used in taxonomy. Credit: Taxonomic ranks, by Awkwafaba found on Wikimedia under a CC BY-SA 4.0 license

For example for Xanthoria parietina, its taxonomy would be: 

Fungus > Ascomycete > Lecanoromycetes > Teloschistales > Teloschistaceae > Xanthoria > parietina

As you can see, these are mainly Latin words. 

Now that you know some common species in the urban ecosystem, you will be able to identify them when you walk down the street !
How fun is it to greet other organisms !? 


The trunk is full of Xanthoria parietina that we have already seen earlier. Between the Xanthoria parietina you will find a few different species like a specimen of the genus Physcia. The maculae of Physcia – which are the whiter coloured areas on the thallus – are quite clear in the pictures below. You will also find Lecidella elaechroma (second photo). This lichen is crustacean-like and has black apothecia on an almost transparent white thallus. It is quite small, keep an eye out!

If you look at the low wall behind the tree, you can see Xanthoria parietina but on rock.

Above the wall there are also lots of different crustose species. The white lichen with the black dots in the middle of its thallus is Pertusaria perfusa. This black dot is the apothecia. The thallus is whitish-grey to greenish in colour. This lichen is regularly found on memorials, siliceous rocks and walls. There are also Phaeophyscia orbicularis that we have already seen and Lecidella elaechroma.


To access a determination key, I recommend this link which presents the common lichens in town in a schematic way. Thanks to this walk, you have been introduced to almost all terms. 

This presentation, created by UCL, introduces tree identification and follows a series of questions to identify the species.

Finally, for more details on lichens in Belgium, I recommend the determination key for macrolichens from Belgium, Luxembourg and Northern France, available online here

If you want to go further in identifying lichens, I suggest you look into these books:

  • A great book in English (the one I use), which helps identifying lichen species in Great Britain, but also often found in mainland Europe:
    Dobson, F. S. (2018). Lichens: an illustrated guide to the British and Irish species. Richmond Publishing.
  • An identification book in French, for epiphytic (on branches) and corticolous (on bark) lichens :
    Van Haluwyn, C., & Asta, J. (2014). Guide des lichens de France. Lichens des arbres. Belin.
  • An identification book in French, for terricolous (growing in the soil) lichens :
    Van Haluwyn, C., Asta, J., & Boissière, J. C. (2014). Guide des lichens de France. Lichens des sols. Belin.

See you soon at the Place du Sablon! 👇🏼👇🏼

If you don’t continue the walk, can you give us feedback on your experience here? It will help us improve !

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