BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 1 ~ Department of Plant Science
DIVERSITY OF LICHENS
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 2 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 3 ~ Department of Plant Science
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.
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 4 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 5 ~ Department of Plant Science
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).
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 6 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 7 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 8 ~ Department of Plant Science
Figure1.3 Powdery lichen (leprose) growing on dried bark of tree
Figure1.2 Crustose lichen species growing on tree bark in partial shade
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 9 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 10 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 11 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 12 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 13 ~ Department of Plant Science
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
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 14 ~ Department of Plant Science
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.
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 15 ~ Department of Plant Science
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?
BIO102: Plant Diversity
OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD
www.bupoyesiku.net ~ 16 ~ Department of Plant Science
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