bio102: plant diversity - olabisi onabanjo...

BIO102: Plant Diversity

OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD

www.bupoyesiku.net ~ 1 ~ Department of Plant Science

DIVERSITY OF LICHENS

http://www.bupoyesiku.net/




Contents Topic: Diversity of Lichens........................................................................................................... 3

Objectives................................................................................................................................... 3

Reading Assignment ................................................................................................................... 3

Lecture ....................................................................................................................................... 3

Introduction ............................................................................................................................... 4

Main Content ............................................................................................................................. 4

Background of Lichens ............................................................................................................ 4

Reproduction in Lichens .......................................................................................................... 5

Vegetative .......................................................................................................................... 5

Asexual method .................................................................................................................. 6

Classification of Lichens .......................................................................................................... 6

Characteristics of Lichens ........................................................................................................ 7

Diversity of Forms in Lichens ................................................................................................... 7

Habitats of Lichens................................................................................................................ 12

Ecology of Lichens ................................................................................................................. 12

Economic uses of Lichens ...................................................................................................... 13

Conclusion ................................................................................................................................ 14

Summary .................................................................................................................................. 15

References/Further readings/Links ........................................................................................... 15

Test Yourself Questions (TYQ) ................................................................................................... 16





Topic: Diversity of Lichens

Objectives

In this lecture students will learn the following:

Awareness and knowledge of the Lichens

Acquisition of hands-on skills to identify members of the Lichens around us

Commercial importance of lichens

Ecological contributions of lichens to our environments

Reading Assignment

In addition to the discussion in this lecture read current textbooks in the main

campus library of Olabisi Onabanjo University Ago-Iwoye and visit:

[email protected]; ilearn.bupoyesiku.net for the online

lecture.

Lecture

Lichens are mostly land dwelling plants. If you are looking for an example of

marriage of alliance, look no further than the lichens. This remarkable

cooperative marriage is composed of two different types of organisms from

different kingdoms. One type from the kingdom fungi is called the mycobiont and

the other types come from kingdom monera and algae they are both called

photobiont, because they are the photosynthetic partners. The participating types

combined to produce a new organism different from any of the participating

types.

Lichens play a few key roles in the natural ecosystems. Like bacteria, lichens

with photobiont partner are capable of fixing nitrogen into nitrate, in nitrogen

deficient habitats, for the use of other plants.


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BIO102%20LICHEN.docx




In today’s lecture, we shall be discussing the lichens, which consist of mainly two

unrelated organisms in one body different from either partner. For those of you

with focus to major in lichenology, as well as those that require the knowledge in

various fields of study, you will gain more understanding about the unusual

alliance of Lichens and their contributions to our ecosystems, particularly their

medicinal and economic importance to humans.

Introduction

Lichenology is the study of lichens. Scientists that studies Lichens are called

lichenologists. Lichen (Greek=tree moss) is not a single plant, but a partnership

of two unrelated plants living mutually together. It is better to think of lichen

partnership as controlled parasitism rather than symbiosis. We have examples of

fungus and cyanobacteria, and fungus and single celled algae. Similar

partnerships (Mycorrhiza) do exist between fungi and roots of vascular plants.

Lichens are fascinating and unusual species, distinct from other plants. The

important fact is that lichens are unique among other plants as a single organism

derived from two unrelated living organisms. Lichens relationship with the

environment is very different from that of any given organism; they occupy

inhospitable places that other organisms could not survive. They are discussed in

this lecture because they have traditionally been grouped with fungi. Although no

clear evolutionary connection with fungi, except for they share reproductive

structures with fungi.

Main Content

Background of Lichens

Lichens are primarily terrestrial. It has been estimated that the number of

different lichen plants range between 13,000 and 18,000 species belonging to

500 genera. Principal partners in a typical lichen body include fungus

(Ascomycetes and Basidiomycetes), Cyanobacteria and Algae. Lichen thallus





shape and color are determined by the fungus the major partner. The minor

partners algal or cyanobacteria partner are sandwich between the upper and

lower layers of the major partner. It is important to know that both algae and

cyanobacteria partners can survive as a free living, but the fungus partner can

never survive for long without a compatible minor partner.

Reproduction in Lichens Some of the important modes of reproduction in Lichens are as follows:

Vegetative

Asexual

Sexual

Vegetative

Lichens can reproduce by vegetative propagules; Soredia and Isidia. Soredia are

tiny powder (20-100 μm dia.), which are restricted to localized areas of the thallus

called sorelia, developed along the apices or margins of the thallus lobes or on

the stem Fig1.1). The Isidia are tiny outgrowth of the thallus (50μm -1 mm high)

vary in shape depending on species from bulbous to cylindrical to branching and

tentacles. Both Soredia and Isidia composed of major and minor partners and

are dispersed by wind and animals.

B

A

Figure1.1 Vegetative propagule- Soredia (A) in sorelia (B).





Asexual method

In asexual reproduction only the major partner fungus is involved. Many fungal

partners have been observed to produce asexual propagules in globose structure

called pycnidia, which resembled perithecium in fungi. However it is important to

note that while asci in a perithecium produce sexual spores, the pinhole pycnidia

contain asexual fungal propagules.

Sexual methods

In sexual reproduction only the fungal partners are involved. The most commonly

used sexual structure is apothecia; a circular and cup-shaped (1 mm- 2 cm long)

commonly sitting on the surface of thallus while immersed in few species.

Classification of Lichens

Classifications of lichens are never stable. Some lichenologists believed that

lichen should have a separate division called Lichenes while others were of the

opinion they should remain as different division under the kingdom Fungi,

because of the shared reproductive structure. However, lichens are classified by

only the fungal partner. In this lecture we shall classify lichen members into two

broad categories based on the origin of the fungal partners. They include the

Ascolichen and Basidiolichen. Nevertheless, it is important to know that

Ascolichens cover 95% of the total lichen members. And the most common

photobiont partner of the lichen is Nostoc, and is abundantly in most jelly lichens.

Other method of classification is based on the habitats.

Bark – corticolous

Decayed wood – lignicolous

Leaf – follicolous

Moss – muscicolous

Rock – Saxicolous

Soil – terricolous





Characteristics of Lichens

The fossil record of lichens is scanty. The oldest fossil lichen is estimated to be

400 million year old (MYO).Other characteristics of Lichens include the

followings, rigid cell walls cemented with cellulose and hemicellulose (as in plant

cells) and chitin (as in animal cells)

Diversity of Forms in Lichens

Although numerous lichen forms exist, despite this all lichens have a similar

internal morphology.

Two groups of lichens will be discuss here; Ascolichen and Basidiolichen. In both

groups forms are based on thallus growth pattern and fruiting bodies.

Ascolichens are traditionally grouped into three based on their thallus forms;

crustose, foliose and fruticose (Fig 1.1).

Crustose (Crumbs)

This is the simplest form of lichen (Fig1.2, 1.3, 1.4). It resembles bread crumbs

attached strongly flattened on the substrate. Growth pattern is radial having

apical growing point at the margins and center remains the oldest region. For

ease of identification on the field you may need to know the following hints.

Thallus edges flat, unlobed and closely attached to substrate

Thallus hard to remove without damaging substrate or lichen

Alga or cyanobacteria usually dispersed

Unlobed leprose and squamulose inclusive





Figure1.3 Powdery lichen (leprose) growing on dried bark of tree

Figure1.2 Crustose lichen species growing on tree bark in partial shade





Foliose (Leafy)

Foliose lichens are leaf-like structure, attached to their substrate by root-like

rhizines (Fig1.5). The thallus is profusely lobed and raised above the substrate in

many species. They have the under surface being lighter than upper surface.

Growth takes place at the margins of the lobes as can be found in Cladonia spp.

For ease of identification on the field you may need to know the following hints.

Circular growth, lobes

Small rootlets called rhizines attach it to substrate

Dorsal and ventral layers color different

Algal mat in middle of fungal dorsal and ventral layers

Figure1.4 Squamulose lichen (pebble-like) growing on soil





Fruticose

Fruticose or umbilicate lichens attached to their substrata by a holdfast

(Fig1.6). The main body of the lichen is either erect or pendulous, and

commonly profusely branched like shrub or tree. Growth takes place at the

ends of the stem-like thallus. Field identification hints include the followings.

Round branches with its fungal layer outside, its algal layer within

No root-like rhizines

vertical or pendulous growth pattern

odd-shaped structures such as wine glass, strap belt

Small rounded shrub-like growth or small tangled beard-like

Hanging down from the substrate by means of holdfast disk

Thallus is circular in cross-section.

Figure1.5 Foliose lichen spp. growing on twig and

branches of plant





Basidiolichen

This group of lichens is very few compared to Ascolichen. Most common genera

in the rainforest Biome in southwest Nigeria include Multiclavula and Omphalina

(Fig1.7).

Figure 1.7 Basidiolichen. A=Multiclavula spp. B=Omphalina spp.

Basidiocarp

Thallus

A B

Figure1.6 Fruticose lichen spp. growing on woody electric pole and shrub twig in

open situation





Habitats of Lichens

Lichen habitats range from the Tropics to the Polar Regions. You can find lichens

growing on any parts of the tree (bark, twig, branch, leaf surface) except root

beneath the ground. Other habitats include boulder, rock, stone, decaying

woods, humus soil, and tundra permafrost soil and desert sands. Few are found

in water, for example Peltigera spp.

Ecology of Lichens

Although all lichens grow slowly except for the fruticose. They grow at a rate of

about 0.5 to 5 mm per year as measured by the expansion of their outline.

However, fruticose lichens grow vertically and rapidly up to 20 mm per year

provided the substrate is long-lived and stably undisturbed. It is quite common for

a lichen to have a lifespan of several centuries for example, crustose lichen;

Rhisocarpon geographicum was estimated to be over 10,000 years old!

Lichens are important species in the world ecosystems as they occupied the

most inhospitable environments. Although lichens are known for symbiotic

alliance.

Almost all lichens contain fungi from the division Ascomycetes and are easy to

recognize by the fruiting bodies. The role of the fungal partner (mycobiont) is to

protect against extreme light intensity and evaporation and to absorb water and

mineral nutrients. The photobionts (Cyanobacteria and Algal partners) synthesize

organic nutrients from carbon dioxide and water in the presence of light. Certain

photobionts also produce yet other nutrients, nitrate, ammonium and other

nitrogen compounds. Almost all living plants directly or indirectly depend upon

lichens for nutritional requirement. It will be interesting to know that a photobiont

partner, cyanobacteria is capable of fixing nitrogen by combining nitrogen gas

from the atmosphere with hydrogen; an important ecological role that help

support other life forms. Nitrate produced by this minor partner are used by other





organisms that cannot convert nitrogen to useable energy for the formation of

proteins, chlorophylls and DNA.

Nitrate from decomposing lichens help fertilize the surrounding soil and stimulate

plant growth. You will recollect in lecture on bacteria, similar association between

bacteria and the root nodules of vascular plants, legumes; fixes nitrogen in

nodules of legume roots and enhance soil fertility balance. Like bacteria, Lichens

are known to be potential biodeterioration of artworks and objects of historical

and cultural importance, such as monuments and synthetic materials; cloths,

paper, leathers, optical lenses, glasses and almost any materials possible to

imagine.

It is also known that lichens are sensitive to environmental pollution. And found to

be effective biomonitor of environmental pollutants. Fruticose lichens are mostly

sensitive to air pollution. Absence of this group from a place indicates poor air

quality.

The role of lichens in soil formation cannot be overemphasized. Lichens help to

form soil by physical and chemical processes. They release carbon dioxide

through respiration, which dissolves in water and forms carbonic acid capable of

dissolving rocks into soil. Physically lichens are capable of penetrating rocks

causing them to fracture and disintegrate; the fungal bodies of lichens expand

and contract with changes in temperature and humidity. It has been observed

that secondary metabolites of lichens react with metals in rocks to produce

organic complexes that help soil formation. Many lichens grow on the soil

surface, protecting it from erosion and enriching it at the same time.

Economic uses of Lichens

Besides the ecological role, Lichens have a great economic value to humans,

animals and plants. It will also interest you to learn that the qualities that make





Lichens important ecologically also make them important source of foods and

medicines. Most lichens generally are bitter tasting and provide reduced

nutritional value and palatability to the ecosystems. Human consumption of

lichens is limited. Only the genus Umbilicaria is reported to have been consumed

by humans.

The current trend in the study of economic benefits of lichens have shown that

they are traditionally a valuable sources of dyes use to color wool and fabric.

Some genera of lichens are known to have natural antibiotic properties. A

common example is Usnea spp. use commercially for preparation of first-aid

ointment and other products. Polysaccharides from the lichens have been shown

to inhibit replication of the HIV virus in laboratory tests

Other medical uses of lichens include preparation of laxatives, deodorants,

expectorants and tonics.

Lumbermen often contact dermatitis through constant exposure to lichens called

“woodcutters eczema”. This allergic reaction is as a result of various lichen acids.

Examples of lichens responsible for dermatitis allergies in humans include

genera of Alectoria, Cetraria, Cladonia, Evernia, Lecanora, Parmelia, Physica,

Usnea and Xanthoria.

Lichens are also used as component of flora arrangement by florists and in

landscaping and building model by architects

Conclusion

You must have learnt how to recognize lichens in the wild, and the diversity of

their divisions. Habitats to find many of the Lichens as emphasized here.

Existence and functioning of the ecosystem partly depend on lichens. There is a

need for further research as to discover more commercial and ecological uses of

lichens.





Summary

Having study this lecture, you should:

Have some understanding of different types of lichens

Have a better idea of the characters that separate lichens from other plants

Be ready to look around your environment for the common lichen members

Develop skills to distinguish groups of lichens in the wild

Have knowledge of ecological and economic benefits

References/Further readings/Links

Reference

Hirabayashi K, Iwata S, Ito M, Shigeta S, Narui T, Mori T et al. (1989). "Inhibitory

effect of a lichen polysaccharide sulfate, GE-3-S, on the replication of human

immunodeficiency virus (HIV) in vitro.". Chem Pharm Bull (Tokyo) 37 (9):

2410–2.doi:10.1248/cpb.37.2410. PMID 2575016.

Questions for further readings

1. Why Fungi are not Lichens?

2. Are lichens decomposers?

3. Is lichen a producer or consumer?





Test Yourself Questions (TYQ)

Matric No Department Attendance Code Session/Student’s Level

AC_______________

Question TRUE FALSE

1. Lichen is made up of two related organisms

X

2. All Lichens are photosynthetic organisms X

3. Algal is mycobiont partner in a lichen

X

4. Pycnidia is an asexual propagules in lichen X

5. Association of algal and fungal is symbiotic X

6. Soredia and Isidia are sexual propagules of lichens X

7. Fruticose lichens are leaf-like

X

8. Sexual reproduction in lichens involve only the mycobionts X

9.Lichen on the rock is called terricolous

X

10. Lichen fixes nitrogen

X


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