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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

http://www.bupoyesiku.net/

OLABISI ONABANJO UNIVERSITY PLS201: CRYPTOGAMS

Updated 1st January 2020

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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




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




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).




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




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.




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.




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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