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
|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|
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.
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 1,473,699 times the size of Wales (as every schoolboy knows a 'Wales' is the standard unit of measurement of surface area).
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.