Baden-Württemberg - Lichens of Wales

The lichen species are for the most part
white-gray to bluish-gray, greenish-gray, or
yellow-greenish, rarely brown, yellow or orange
colored. Although the color of the thallus is an
important character, the proper specification of
thallus color is problematic. The lichen colors
are frequently difficult to describe. At first the
practice was to show to the reader a key little by
little, whatever he was to understand under many
color descriptions. Here the aid of color photos
is a way around the deficiency of our language.
Thus documenting a picture of Parmelia
caperata or the beard lichen Usnea, it becomes
understood what blue-greenish to
yellow-greenish is in lichens, while the mere
color description without picture documentation
always leads to further misunderstanding.
3.2.2 Structure and Organs of the Thallus
Growth Forms
Three main types of growth forms of lichens are
described: crustose lichens with pure crustose
thallus, foliose lichens with leaf-like, ± lobed
thallus and fruticose lichens with shrubby to
filamentous thallus. Between foliose and
crustose lichens are intermediate forms with
squamulose thallus and such crustose lichens,
whose margins are clearly lobed. These crude
divisions do not do justice to the majority of the
forms of the lichens. They are however very
useful for a first response. The more precise
characterization or the growth form arises from
the preparation of key parts. The group of
gelatinous lichens is characterized by the
gelatinous consistency of the thallus (in the moist
condition swelling gelatin-like); they can include
various growth forms.
Especially in the level of organization the
crustose lichens are differentiated into many
types of thallus forms, whereby above all their
position is accepted on the degree of division of
the thallus and upon nature of the upper surface.
Organization and Nature of the Upper
Surface of the Thallus
The upper surface of the foliose and fruticose
lichens is – apart from the occurrence of isidia
and soralia (see below) – smooth to rugose or
from time to time weakly organized raised
ridges. In many crustose lichens the thallus is
cracked or subdivided into ± separated areoles;
it may even consist or more or less closely
crowded to scattered granules or sometimes
completely mealy disintegrate. One speaks of a
coralloid thallus when it is made up of elongate
branched “granules.”
Organization of the Thallus of Crustose Lichens
Egg-shaped, varnish-like, or membranous
(not or scarcely cracked)
Cracked
Cracked areolate (reticulate cracked, thereby
consisting of areas, area flat)
Areolate (clearly separate areas)
Warty areolate (Areoles convex)
Squamulose (Areoles isolated, in the form of
± overlapping other areoles, the edges often
crenate or lobed, usually raised from the
substrate at the edges; if squamules more
strongly divided of clearly erect: crossing over to
“small foliose”)
Upper Surface Condition of the Thallus of
Crustose Lichens
Mealy (very finely granular, “dusty”; when
the upper surface is totally disintegrated it is
called “leprose”)
Granular (finely or coarse granular)
Warty (Thallus uneven, unevenness warty
convex)
Wrinkled (Thallus irregularly uneven)
Coralloid (of coral-like branched granules)
Smooth
Soralia and Isidia
The soralia and isidia are among the most
important diagnostic organs of the lichen thallus.
They serve for vegetative reproduction.
Existence and form of soralia and isidia are
species specific characters.
Isidia are usually simple peg or clavate form
to coralloid branched or even almost spherical
outgrowths of the upper side (see illustration),
they are easily broken off and may grow into
young lichens. They are generally colored
similar to the thallus and are even anatomically
not basically constructed other than the thallus
from which they are an outgrowth.
Soralia are a somewhat mealy, usually whitish
to greenish-gray outgrowth of the thallus, which
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