Sunday, February 8, 2009

A lichen Aspicilia calcarea

I am an amatuer naturalist trying to discover what lives in my garden.

Those following my recent posts will know I have been on something of a mission to blog the lichen-life on the exterior of my house. Photo 1 shows yet another inhabitant - another crustose lichen (for those unfamilar with lichens, see my post here).

Incidentally, photo 1 also captures (upper left) our old friend, the moss, Tortula muralis.

After a little research I'm confident the lichen here is Aspicilia calcarea. Characteristic features include the cracked, white thallus (the main body of the lichen) and the irregularly shaped apothecia (the black, spore-liberating cups) sunk into the thallus. The books tell me that A. calcarea is common on hard calcareous walls etc. in lowland Britain. Photo 2 shows a closeup.

For those wanting a cheap photographic key to some common, British, urban lichens incidentally, I recommend the short-form guide sold by the good people of the Field Studies Council . For something more detailed the book Lichens (Frank S.Dobson) is especially good.

I'm fond of lichens. Their ability to shrug off the worst the elements can throw at them gives them, for me, an appealing minature 'feistiness' - I picture them squatting on exposed boulders on windswept mountain sides goading the rain "Come on! Give me your best shot! Is that all you've got pal !?"

On a more rational note (!), something that intrigues me is the diverse array of colours and shapes lichens adopt. I have no deep expertise in evolutionary ecology but as I understand it, there is nothing haphazard about the forms taken by species. Life is hard and an ever-present scarcity of resources and the threat of predation and disease is a constant imperative, forcing species to individually specialise in unique methods of suvival. A famous example is of course the beaks of finches, with different species having been driven to evolve different beak-shapes to allow them to eat different nuts and seeds. Different birds evolving different beaks to help them occupy different feeding niches is one thing. The distinct environmental pressures or purposes that drive two lichens such as A. calcerea and C. citrina to adopt such different colours and (once you look closely) really quite different textural forms, when both seemingly occupy the same ecological niche of lowland stone (indeed, the same household windowsill in my case!) - I struggle to guess. Do leave a comment if you can help me.

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