Baden-Württemberg - Lichens of Wales

consists of an accumulation of tiny, ± spherical
reproductive granules, the soredia. The soredia
usually lie close to the algae layer of the thallus.
Position and form of the soralia are species
specific distinctions. They may sit upon the
surface, at the edge or on the ends of lobes, have
a long streak linear or rounded outline and be
concave to strongly convex or lip-form. The
various types of soralia are considered in the list
of technical terms. An oversight of distinct
forms results in the following illustration. Many
lichen species produce no normal bordered
soralia, but large areas of the upper surface
becomes sorediate or even the entire thallus.
Rhizines, Cilia, and Pseudocyphellae
On the underside of foliose lichens are found
attachment organs which serve to attach the
thallus to the substrate. The most frequent are
rhizines (fastening filaments); which may be
regarded as simple, forked or like a brush or
bottle cleaner (Illustrated on page 729). In the
case of many foliose lichens the underside is
covered with a ± thick hairy layer, in others a
network develops. Soil-dwelling fruticose
lichens sit loosely on the substrate, rock and bark
dwellers are generally attached with a somewhat
broader base, an attachment disk.
In the case of some few species of foliose and
fruticose lichens the indigenous flora the lobe
margins or lobe ends are provided with
characteristic setiform projections (also known as
cilia) (See page 75). Pseudocyphellae are also
important diagnostic structures. These are very
delicate point or linear whitish eruptions or
lacunae in the cortex above all of foliose and
fruticose lichens (See page 75 and 276).
Sometimes the lines are reticulate and sit upon
very weakly raised ridges (See page 663).
3.2.3 Structure of the Thallus
In the lichen the fungus envelops with a mesh of
filamentous structures (hyphae) usually
numerous single, rarely multicellular algae the
partner species. The algae are commonly
concentrated in a zone, in the case of gelatinous
lichens mostly distributed over the whole thallus.
The residual space in the lichen is taken up by
the fungus partner, which also by the
arrangement of the hyphae often determines the
form of the lichen.
Toward the outside the fungus hyphae often
produces a thick protective, especially structured
cortex. The algae layer, in which the algae are
entwined by fungus hyphae, lies under the cortex.
Under the algae layer is developed a usually
relatively thick medulla of loosely interwoven
hyphae. In the case of crustose lichens, the
thallus with the medulla rests upon the substrate.
In the case of foliose and fruticose lichens, a
cortex is usually also developed on the
underside, i.e. the lichen is encircled by a
surrounding cortex layer. Special attachment
organs often also occur on the underside, e.g.
rhizines.
The cortex in section shows a structure of
more or less rounded-multiangular cells (see
page 24), which are called paraplectenchymous
or pseudoparenchymous (reminiscent of a
parenchyma of higher plants). If they are more
parallel structured of elongated cells, they are
called prosoplectenchymous (see page 24).
Almost all lichen fungi belong to the
ascomycetes, to which e.g. also are numbered the
cup-fungi and morels. Yet the lichen fungi do
not often occur free-living, but have become
completely dependent upon the lichen symbiosis.
The lichen algae belong for the most part to the
green algae, to a smaller degree to the blue-green
algae or cyanobacteria. Each lichen species is
characterized by a specific fungus, occurring
only in it, as well as by a mostly definite species
of algae. One and the same alga species may
occur in various lichen species. For an oversight
of the most frequent algae see page 64 and
illustrations on page 64 and 65.
3.2.4 Form and Structure of the Fruiting
Body
General
Fruiting bodies are relatively frequent in the case
of crustose lichens. Many native foliose and
fruticose lichens on the other hand do not
commonly fruit and reproduce instead
vegetatively with the help of soredia, isidia,
thallus fragments. Conversely, as a rule,
regularly fruiting species do not produce
vegetative reproductive organs.
Fruiting bodies appearing in lichens result in
connection with sexual process of the lichen
fungus. Since almost all lichen fungi belong to
the Ascomycetes, the fruiting bodies are the so
called ascocarps. When the spore generating
tissue (hymenium) lies open to view, it is an
apothecium, if it is enclosed in a more or less
spherical structure and only open to the world
10