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With a life's experience of teaching field studies in the Forest of Dean, Brian Cave explores the ecology of rural France. More Info

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An English Naturalist in France

An impressive Lichen

August 10, 2015

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There had been a heavy rainstorm with serious wind overnight.  That August 8th the trees were in full leaf.  Branches were hanging heavy with walnut fruits. I  imagined that the buffeting  would bring down the branches.   I foresaw damage.  In the morning I went to look for it.  Joyfully I found none,  But there on the grass I saw what looked like a lump of alga, just like one might find on a rocky shore.  I supposed that someone must have dropped it – but why or who?

But then I saw another.   Picking a mass up I quickly realised that it was a lichen.  I wedged it on a lower branch of the walnut tree to take a photo – see to the left.   The branches of the lichen were about thirty cms long and between one cm and two centimetres wide, with the appearance of  wrinkled grey green ribbons.

Along these ribbons were various mushroom shaped growths,  the more mature with a spread of about 5 mm and a similar height.  These are called apothecia and are structures of reproduction.

A glanced up into the tree to look for more but could not.  I have been walking daily beneath this tree for seventeen years and have never noticed such great growths before.  There are various lichens on the tree and I would not pretend to know

all the species.  They are after all a most difficult group of species to study.  It seemed to me extraordinary that I had not noticed this large growth of lichen before.  It is really impressive.   It reminded me in appearance of the ‘Spanish Moss’ on the trees in Florida.  That, by the way, is not a lichen.  I searched the tree using binoculars and still I could not be certain of locating the species in the high branches, but I guess that some growths must be up there.

The features of this species are fairly obvious and I soon understood it to be (i.e. after consultation with certain well known books on lichenology) to be a species of Ramalina – in fact R. fraxinea.

Is it common in France, I pondered. So I went to the French INPN site [ Inventaire National du Patrimoine Naturel] 

It surprised me to see that it was only registered in four widely separated districts of the country, mostly in Normandy, but also in the Gers, South East and East – all widely separated. I believe that it must be more common than that.  But there are few people who have any knowledge at all of such things.  Further it is difficult for me to contact the specialists who do exist.  And I fear that as an amateur who is an Englishman it is difficult to communicate.

Apothecium in section

 

The structure and growth of Lichens.   The apothecia of these specimens were so large that I decided to examine sections of them under the microscope.  There was nothing exceptional but nevertheless interesting.  To the left is a micrograph of a section.  The surface of the apothecium  is to the left. Deep in the tissue  can be seen the little round green cells which are those of a green alga. One has become detached and is suspended in the water used for mounting the specimen on a slide.  These algal cells produce foodstuffs via photosynthesis.  The surrounding tissue is a fungus which is absorbing nutriment from the alga.   A complete co-harmony where each organism supports the other in some manner, although perhaps the fungus has the upper hand.  The whole design of the co-partnership demands on the union however, for it seems that if one attempts to grow the fungus without the alga, all that grows is a shapeless mass. So in some manner the alga is imparting some form of ‘genetical’ information in the relationship.  The alga reproduces essentially by splitting in two.   The fungus reproduces by oval structures called  ‘asci’ and in these there are eight spores.  These are released at the apices of the asci on the surface of the apothecium and are  distributed in the air.  One supposes, as in normal, that the ascospores have only one set of chromosomes.  Two spores would have to meet up in growth to create a new fungoid growth. And – such a young growth would have to meet up with some fresh algal cells to begin a new lichen structure.   It would seem that much is staked against these organisms undergoing all that. 

It is not surprising that most lichens evade such a sexual process and just reproduce by creating small groups of cells consisting of both fungus and alga and letting these asexual ”soredia’ fall off as a powder to get distributed.  But Ramalina fraxinea appears to lack these ‘soredia’  . It only has the apothecia which would seem to demand a genetical sexual type of cycle  which would demand a meeting together of alga and fungus at a very early stage in development. 

How did these magnificent growths begin high up in my walnut tree?

by Brian Cave. Find out more about Brian Cave here.

Categories: Lichens, Trees