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

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

Physcia - '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.

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