Baden-Württemberg - Lichens of Wales

Foundations and Illustrations
1 Introduction
1.1 What are lichens?
Lichens are not homogeneous organisms, but
consist of two entirely distinct organisms, and
indeed of one fungus and at least one alga, living
together in close contact. Their double nature is
outwardly not recognizable. Often the lichen
resembles neither of the synthetic partners. The
lichen is first rate in numerous specific
attainments in structural independence. These
are possible only through ”cooperative work” of
the partners. Several phenomena are only known
from this plant group.
One such, the common living together in
harmony by two different organisms one calls
symbiosis. Symbiosis is known in several
animal and plant groups, yet rarely is the
symbiosis so perfected as in the case of lichens.
The lichen symbiosis brings fungus and alga
substantial profits. The fungus receives
carbohydrate from the algae necessary for its
existence. The alga is protected in the
enveloping intertwining fungus from rapid water
loss, from intensive solar rays, or from easy
clutches of algae feeding animals. With the help
of symbiosis in the lichen the involved fungus
and alga have their ecological potentiality
considerably widened and are in the position, to
colonize habitats, where each alone could not be
successful.
The vegetative body of the lichen is known as
a “thallus.” According to the growth form of the
thallus, one differentiates crustose lichens, leafy
or foliose lichens, and fruticose lichens having
shrubby to beard-like forms, foliose lichen lobes,
more flat developing thallus, and crustose lichens
crust-like or scruffy, the thallus grows together
with the substrate, from which they can not be
removed uninjured. Gelatinous lichens are brittle
in the dry state, when moist they are swollen and
more or less like tough-gelatin (see further
below).
1.2 The Ecology of Lichens
Lichens are distributed world wide. Also in
Central Europe they are species rich represented
in a truly large number of forms and variety of
colors. We find them on tree bark and wood, on
rocks, walls, grave stones and tiles, on the soils
of open forests, in heaths and moors. Most of the
species live under very specific habitat
conditions. One knowing these conditions, can
search according to the species.
Many lichen species live almost exclusively
on bark, others on wood, still others on
calcareous rock (e.g. limestone, or dolomite) or
on lime-free silicate rock (e.g. granite, gneiss, or
basalt), others live on soil.
The mostly epiphytic, i.e. species living on
tree bark do not occur equally on all tree species,
but display a definite emphasis. One reason for
that is that the barks of various tree species
exhibit differing chemical-physical properties,
above all, differing pH-conditions produced have
accommodated single lichen species under
certain conditions. Many occur on “acid” bark
(e.g. spruce, birch, or alder), others on “base-
rich” (bark) (e.g. walnut, Norway maple, or
alder). Many species are limited to smooth bark
and then disappear, when the tree, with
increasing age, develops a rough cracked bark;
others establish first on such older stems. Such
relationships between the lichen species and the
habitat conditions, hence ecological
characteristics, can be fully valued key
characters.
Similarly single lichen species are more or
less limited to certain substrate attributes,
“preferences” by definite light and moisture
conditions. Many are “sun species”, others
“shade species”, many are limited to cool, humid
habitats and are more often found in forests,
others tolerate even sunny, dry conditions and
live on free-standing trees. Some are able to live
on rain-protected flanks and in bark crevices –
they cover their water budget from the water
vapor of the air --, others are dependent upon the
frequent soaking of the thallus with water. Such
ecological characteristics are presented in the
main part of the species descriptions.
One of the fundamental properties for the
appreciation of the biology of lichens is the
inability of these double organisms to continue
constant metabolic activity, as we know it in the
flowering plants during the vegetative period as
an indedpedent activity. Lichens can not regulate
their water budget. They have no true roots.
They can neither actively take up water nor in the
case of dryness appreciably slow down the water
loss; they have no evaporation protection. This
means that in case of dry weather they gradually
lose water that is necessary for the maintenance
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