Introduction to lichens

Lichens on Trees - common, easily identifiable species
high resolution poster - it can be
downloaded here 

It's an A2  PDF (which is 4 times A4, but the will resize to A3 or A4).

There is a a bit of a lichen bonanza on this branch
Leafy ash lichen -Ramalina fraxinea (long trailing one on the left - uncommon)
Shaggy Strap Lichen - Ramalina farinacea (bushy one bottom left - very common)
Ramalina fastigata (bushy, 'flasky' one in the middle)Hammered shield lichen - Parmelia sulcata (grey leafy 'hammered metal'- very common)Wall lichen - xanthoria parientina (yellow one near top - very common) also Lecidella elaeochroma & Lecanora chlarotera

I've found that with several difficult groups (mosses being another one), it's difficult for a novice to find a 'way in'. You're immediately plunged into the deep-end - lots of similar, hard to identify species, unfamiliar terminology and resources mainly aimed at experts. For this reason I've created a...

...Beginners Guide to Lichens

What are lichens?
Lichens are fascinating - they consist of a fungus and algae partnership. The fungus benefits from the arrangement because the algae produce food by photosynthesis. The algae benefits by being protected and anchored by the fungus.

When trying to identify a lichen, it's useful to note:

a) the form of the lichen
Crust (Crustose) closely adhering to the substrate.
Leafy (thallose) lobes with root like structures (rhizines).

Bushy (foliose) attached to the substrate only at the base.

b) what is it growing on (the substrate)
On wood - trees, fences
on rock / brick
on the ground - amongst, 
moss, grass, soil
c) does it  have fruiting bodies
These can take several forms, the most obvious ones being 'flasks', 'saucers' or 'spots' (apothecia)*

E) what colour is it -
 in the case of the leafy and bushy lichens it's useful to look not at the colours underneath as well as on top of the thallose
'Starter Species'
I find that a big part of the 'way in' for any difficult group is to have 5 or 6 'starter species'. These are common and easily recognised - not easily confused. Once I have learnt to recognise these then I can start to add to my knowledge.
Xanthoria parietina
- Yellow & leafy, on wood & rock

Parmelia sulcata
- 'hammered metal' pattern on thallus

Evernia prunastri
- several look similar to this
but look for white (not green) undersides

- fine and beard-like
U. subfloridana is the commonest

- 'whiskers' on thallus P. tennella & P. adscendens are the commnest

Lecidella elaeochroma (black) and Lecanora chlarotera (white)
 -individually these are confusable
with other species,
but when together (as they often are) they are likely to be these species

Indicators of  Pollution
Many lichens are sensitive to atmospheric pollution. Different species are sensitive to different pollutants. For this reason the can act as 'canaries' - bio-indicators of air quality.

Ramalina fraxinea (the large straggly lichen in the top photo) is very sensitive to sulphur dioxide pollution. It became extinct in many areas in the 70's. Now with improving air quality it's starting to return.  On the other hand, Xanthoria parietina (pictured is above) is very tolerant of pollution.

My favourite lichen-fact
It's estimated that 6% of the Earth’s land surface is covered by lichens. By my calculations that’s 450 times the size of Wales (as every schoolboy knows a 'Wales' is th standard unit of measurement of surface area).

Useful Links
British Lichens
A guide to lichens on twigs
A key to common lichens on trees in England
Alan Silverside's Lichen pages

Thanks to those who've help with suggestions and information.

*there are other kinds of reproductive structures - namely Isidia and Sorelia.
Get this


  1. From Jan - A great starter guide to an otherwise daunting topic! Thanks for the links too. :)

  2. This is a really wonderful site!

    But I think your calculation on the number of Wales's covered by lichens is out...

    Total land surface area =~ 150,000,000 km^2
    6% of land surface area =~ 9,000,000 km^2
    Wales surface area =~ 20,000 km^2

    Number of Wales sized units covered by lichens =~ 450

    (Still quite a lot!)

    1. Many thanks for pointing that out, you're right I was miles off. not sure what I was thinking there!

    2. ...and thanks for your kind words

    3. You can never have enough Wales'

    4. I agree, I'd like to see it expand to encompasses 'England'

    5. I've downloaded the Lichen leaflet. Thank you very much for your work. Regards from Yorkshire.

  3. Lots of lichens of all kinds in Finistere, Far West of Brittany - 'End of the Earth' (or end of the world, or the land' - Finistere has two mountain ranges, Monts d'Aree in the North and the Montagnes Noires in the South (like Wales) and is also the size of Wales! So the whole of Brittany (Bretagne) would be 40 x the size of Wales! (Love its 'Welshness'
    Thank you very much for this great work on Lichens - and for previous work on trees and buds!

    1. sorr - couple of errors there - Bretagne is four times the size of Wales/Finistere, not forty! And es, in those areas of SSSI, the national parks, there is stll a lot of natural, original mixed deciduous woodland where man species of lichen still abound. The air n the mountains is for the most part very clean, due to the prevailing westerlies, (for the same reason as Wales is, except for the industrial south) but a lot of woodland is falling under the axe due to 'ecological' choices of woodburning as a form of renewabe heating - a shame as old woodland is cleared rather than specific fast growing plantation for converting to pellets for use in burners (efficient and avoids destroying forest habitat and slow growing hardwood)
      Also modern burners are better at rendering energ and releasing lower exhaust gases. Ideally rocket stoves using fast growing hazel or willow would be adequate in a reasonably small thicket for a famil's heating/cooking needs if carefull managed.

  4. thanks for your photos, i'll show your photos to my student in my presentation


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