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Learning with Prof Bup www.bupoyesiku.net Updated 1st January 2020
KINGDOM: FUNGI
PLS201: BIOLOGY OF SEEDLESS PLANTS (crustose lichen)
OLABISI ONABANJO UNIVERSITY | Department of Plant Science
OLABISI ONABANJO UNIVERSITY PLS201: CRYPTOGAMS
Updated 1st January 2020
Learning with Prof Bup www.bupoyesiku.net Page 1
Contents
Contents ........................................................................................................................................................... 1
Introduction ................................................................................................................................................. 2
Objectives ................................................................................................................................................... 2
Main content ............................................................................................................................................... 2
Background of lichen ............................................................................................................................ 2
Members of lichen ................................................................................................................................. 3
Characteristics of lichens ..................................................................................................................... 3
Forms/Habits of lichens ........................................................................................................................ 4
Habitats of Lichen .................................................................................................................................. 5
Ecology of lichen ................................................................................................................................... 5
Economic uses of lichen ...................................................................................................................... 6
Conclusion .................................................................................................................................................. 6
Summary .................................................................................................................................................... 6
References/Further readings ................................................................................................................... 6
Tutorial-marked questions ....................................................................................................................... 7
OLABISI ONABANJO UNIVERSITY PLS201: CRYPTOGAMS
Updated 1st January 2020
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Introduction
Today, we are moving up the evolutionary ladder to look at a unique organism, the
lichens of dual relationship, a marriage between fungus and algae or blue-green algae
(Cyanobacteria). Today’s lecture will harness the interests of those going to become
lichenologists, as well as others needing the knowledge in their various field of study.
Additionally, the study of lichens diversity will make a conscious of our surroundings and
their ecological and economic importance.
Objectives
At the end of this lecture, w will be able to:
1. appreciate the need to study the lichens
2. have a definite feeling of the features that separate lichen from other plants
3. be more confident in identifying lichen in our surroundings
4. appreciate the contributions of lichen to our lives
Main content
Lichen (Greek=tree moss) is a dual plant in a relationship. This partnership relationship
binds mutually together two or occasionally three unrelated cryptogams. We have
examples of fungus from the class of Basidiomycetes binding with Cyanobacteria (green
bacteria) or single-celled green algae, and occasionally, the lichen fungus binds with both
the green bacteria and algae simultaneously. Other similar partnerships (mycorrhizal) do
exist between other fungi and roots of vascular plants, but morphologically and
physiologically differs from the lichens. It is better to think of lichen partnership as
controlled parasitism rather than symbiosis.
Background of lichen
Lichenology is the study of lichens (Greek=tree moss). It is important to note here that
the English word "moss" used to refer to several, what we now consider very different
types of plants. The "true" moss refers to bryophytes, which we shall be discussing in our
next lecture, while other plants morphologically resembling bryophytes are actually “false”
moss. Examples of such false moss include cup-moss refers to the lichen Cladonia spp.,
Irish moss refers to the red algae Chondrus spp. Spanish moss refers to the angiosperm
Tillandsia spp.; club moss refers to the pteridophyte Lycopodium spp. (Welch 1948: 32).
At this point that we can confidently make a distinction of the lichen that resembles the
real moss, we move on to discuss in details the morphological and physiological attributes
of the lichens. The fungus (principal partner) determines the shape and often the colour of
OLABISI ONABANJO UNIVERSITY PLS201: CRYPTOGAMS
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the lichen thallus. The principles of survival in lichen depend on the algae or
cyanobacteria partner, which on their own can survive as free-living, the fungus partner
can never survive to maturity age without compatible algae or cyanobacteria.
At this point, we want to support the belief that lichen involves a mutual relationship in the
sense that neither the fungus nor the green partner grows independently where the lichen
grows. Moreover, the physiological evidence suggests it could be probably more correct
to say that the fungus parasitises the green partners in a controlled manner, which could
be destroying the chlorophyllous cells of the partner.
Members of lichen
Lichen members, derived from three fungi divisions, Ascomycetes, Basidiomycetes and
Deuteromycetes. The three members are Ascolichens (e.g. Cladonia spp.), basidiolichens
(e.g. Omphalina spp.) and deuterolichen (unknown fruit body or sexual cycle). It will be
interesting to know that well over 18,000 species of
lichens belong to about 500 genera. The green partners
include three genera of algae and a genus of
cyanobacterium. Lichen, however, has its unique
species of fungus, while one species of alga found in
many different lichens. It is interesting also to know that
the participating partners grow faster when they are part
of the lichen.
Figure 1. Members of basidiolichens
The fungal partner rarely found growing independently in nature, while the green partner
algal (or cyanobacteria) is known to flourish independently of the lichen. From the
preceding, the fungal partner is used to identify a lichen species.
Characteristics of lichens
The algae or cyanobacteria partner, sandwiched between the upper and lower layers of
the principal fungal partner. A typical lichen consists of a union of fungus (ascomycetes)
with alga (single cell) or cyanobacteria (blue-green algae). Lichens grow very slowly
(minimum=0.1 mm and maximum=1 cm per year).
OLABISI ONABANJO UNIVERSITY PLS201: CRYPTOGAMS
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Forms/Habits of lichens
Lichens, grouped into three growth forms, which have no direct
connection with their natural relationship. They include
1. Crustose (crusty) lichens: coloured patches on bare rocks
and tree bark, attached to the substrate by their entire lower
surface
2. Foliose (Leafy) lichens: grey overlapping leaf-like thalli,
weakly attached to the substrate, margins are lobe-like
3. Fruticose (miniature tree or shrub): attached at one point to
the substrate and hanging down, branched thalli, which are
cylindrical
Figure 2 A-C. Forms of lichens. A=Crustose, B=Foliose. C=Fruticose
B
C
A
A
B
C
OLABISI ONABANJO UNIVERSITY PLS201: CRYPTOGAMS
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Habitats of Lichen
Lichens are majorly terrestrial except for one species that grows wholly submerged on
ocean rocks. One of the reasons for the full range of tolerance of lichen is the presence of
a protective gelatinous substance that enables them to withstand the harsh period of
rapid drying alternating with the wet period. It is interesting to know that while they are
dry, their water content may drop as low as 2% of their dry weight. The opaque upper part
of the thallus prevents much of the light that falls on them. Hence, most of the habitat
extreme conditions do not affect them as they temporarily become dormant.
The followings are examples of where we can find lichens. Bare rock in the blazing sun or
bitter cold in deserts sand, cleared soil, dead wood, tree barks. Others include materials
such as rusty metals, glass, concrete, asbestos and animal bones (in the desert)
Ecology of lichen
As discussed a moment ago that lichen survives in a harsh environment where no other
plant can survive. We shall now look at the physiological process that goes on in healthy
lichen. Photosynthesis in Lichen reaches the peak when the water content in the thallus is
above 65%. Lichen can absorb about 35 times its dry weight. They also absorb nutrients
from the surrounding air and rainwater. Lichens store nutrients and make the habitat
suitable for a new plant that maybe establishes in future.
We must know that lichens are very sensitive to toxic substances, especially sulfur
dioxide, present in the air. Such include heavy metals, radioactive elements, and sulphur.
These toxic substances remain both in living and dead thallus until wholly decomposed.
For our understanding, if we live in a palace with lots of lichens, it is suggestive of
unpolluted clean, healthy air. However, if lichens rarely found in our area, it is suggestive
of polluted unhealthy air. The source of polluted air may include exhaust from vehicles,
generators and heavy equipment; others include industrial smokes and dust. It is of
ecological interest to know that lichens with cyanobacteria partner could fix atmospheric
nitrogen into nitrate that is useable by other plants.
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Economic uses of lichen
Lichens provide food for many lower animals and large mammals (Reindeer and caribou),
however, they are not palatable food to humans because of their acidic nature and harsh
laxative effects. Is emphasised that while lichens were unpalatable, the majority of them
have antibiotic properties. Lichens were used for dyes by the Greeks and Romans. It will
be of interest to us that lichens are used raw material in the preparation of litmus paper,
(acid-alkaline indicator), which turns red under the acid condition and blue under alkaline
condition. Extracts from lichens used as perfumes in scenting soap. The architects and
toymakers used lichens (fruticose) for the scenery of model parking lots, car and
railroads, because of their resemblance to miniature trees and shrubs.
Conclusion
In this lecture note, we have learnt how to recognise the lichens among other plants, how
we can distinguish them from other cryptogams. Lichens are exceptionally sensitive to
environmental pollution, and indicator of the health of our environments.
Summary
Having studied this lecture note, we should have:
1. some understanding of the uses of familiar lichens
2. a better idea of separating them from other groups of plants
3. identification skills
4. understanding of their contribution to our lives
References/Further readings
Welch, W. H., 1948. Mosses and their uses. Proceedings of the Indiana Academy of
Science 58: 31-46.
OLABISI ONABANJO UNIVERSITY PLS201: CRYPTOGAMS
Updated 1st January 2020
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CLASSCODE: DEPT.: MATRIC NO.:
Tutorial-marked questions
1) List the categories of lichens that we know
1. Ascolichens
2. Basidiolichens
3. Lichen imperfecti
2) States reasons why lichens are rare in urban cities
Ans:
1. Sulphur dioxide in high concentration destroys the chloroplast of the algae
partner of the lichens
2. Lichens are sensitive to automobile fumes and industrial wastes
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