No, it isn’t the work of a careless painter, nor the result
of someone disposing of their chewing gum, it’s natural. And not just white patches, but yellow, green,
red and brown; it’s lichen, moss and some kinds of algae.
One of the must-have DVDs of Christmas 2016 was the newly
released film of Swallows and Amazons.
Before the film-makers decided to introduce a hint of espionage, there
was a sub-plot in Arthur Ransome’s book about Captain Flint’s book of his
travels, “Mixed Moss” by “A Rolling Stone”.
Ransome was referring to the proverb, “a rolling stone gathers no moss”,
a reminder that moss grows slowly and likes steady conditions. Moss can be found in damp, shady parts of the
neighbourhood, a nuisance to those whose lawns are “grass mixed with moss”, but
a way of softening the hard, harsh surfaces of pavements and walls. Biologists will tell us that there are over
10,000 species of moss, flowerless plants which spread by spores, not
seeds. Gardeners rely on moss as a
constituent of peat – suffering from over-use these days – and florists use
moss for decoration and to retain water (many mosses can hold over 10 times
their weight of water). In the First
World War, moss was collected and used as a dressing for wounds – a memorial at
Widecombe is a reminder of the amount collected on Dartmoor. Moss was superior to cotton as a dressing for
wounds, being mildly antiseptic. There
is speculation that some birds choose to use moss in their nests for the health
of their chicks. So, if the moss on your
patio or roof is being pecked by birds, it may be for the insects living there,
or to help raise the next generation.
Lichens also generally prefer damp conditions; their biology
is more complex than that of mosses, and even now there are some aspects of how
lichens live that are not fully understood.
The professional society that studies them explains that “A lichen is
not a single organism; it is a stable symbiotic association between a fungus
and algae and/or cyanobacteria.” And I
am not going to attempt to explain that here!
Around the neighbourhood, there are countless patches of
what is called a crustose lichen (crustose simply means that it has a crust)
which can be mistaken for chewing gum on pavements. (Not many lichens have common English names,
and I will leave Latin in the Neighbourhood News to the editor’s fluency.) The commonest species here are very tolerant
to urban pollution; generally, though, lichens prefer an unpolluted
environment, and so you find more different lichens where the air is
cleaner. (My brother points out that he
finds many more lichens when he visits Exeter than in his workplace of Sussex.) Next time you are walking in the
neighbourhood, stop to look at the crusty lichens on the walls. Walls with a lot of lichens are providing the
right kind of conditions; acidity, moisture, quality of air, chemicals in the
stone. So glazed bricks don’t grow many
lichens; older bricks often do. Lichens
are scarce on local granite features, even though the tors of Dartmoor are home
to many. It is all to do with moisture
and pollution. Lichens colonise some
pavements more than others; it may be the type of surface, or simply the amount
of foot traffic from passers-by. Have a
look under a roadside bench to see how they spread where they are
undisturbed. Different crustose lichens
can be found on the bark of trees, usually on the north side of the trunk or
branch, because that is moister. But you
may notice that some species of tree have no lichen, while a neighbouring tree
has plenty. Trees differ in the acidity
and nutrient content of their bark, and lichens grow where the conditions are
just right.
Older garden trees may have fruity or fibrous lichens, and again,
the number and type of lichen depends on the species of the tree. Generally, the tree will not suffer from the
presence of lichen, so if you have some, rejoice – your garden has pure
air.
What’s the use of lichens?
Of course, you can feed your pet reindeer on lichen; they enjoy it. Humans sometimes eat lichen, but it is not
for everyday diets – unless you are desperate, and even then, take care. But from prehistoric times, lichens have been
used to make dyes for wool, and some weavers and spinners still do this. Brown, gold, orange, green, purple, blue and
red colours are all possible, depending on the species of lichen used and the
type of extraction process. And if your
favourite perfume contains oakmoss, you are scented with an extract from that
lichen – despite the name!
The poet John Clare wrote about the natural world. It is perhaps appropriate that his gravestone
in Helpston churchyard in Northamptonshire is covered with lichen. The lichen has spread into the inscription so
that his epitaph now reads “A POET IS BORN NOT MAD”, hiding the final “E”.
(Published in Neighbourhood News, Jan-Feb 2017)
(Published in Neighbourhood News, Jan-Feb 2017)
Keywords: St Leonards, Exeter, history, geography, beauty lichen