Lichen | CEE Academy

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INTRODUCTION

▢ Study: Study of lichens = Lichenology

▢ Definition: Lichens are symbiotic associations between an algal partner and a fungal partner.

▢ Nature:

•
Composite or dual organisms
•
Possess a distinct structure different from either partner
•
Show very slow growth
•
Plant body represented by an irregularly shaped and variously coloured thallus

▢ Partners:

❖ Algal Partner:

◉ Name: Phycobiont

◉ Groups:

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Green algae
•
Blue-green algae or cyanobacteria

◉ Function: Photosynthesis and food production

❖ Fungal Partner:

◉ Name: Mycobiont

◉ Groups:

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Ascomycetes
•
Basidiomycetes

◉ Functions:

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Absorption of water and minerals
•
Protection
•
Attachment
•
Reproduction

▢ Nature of Association:

❖ Helotism:

◉ Definition: Association in which the fungus acts as the master and the alga as the slave

◉ Fungal Role:

•
Absorption
•
Protection
•
Reproduction

◉ Algal Role: Photosynthesis

❖ Alternative Description: Fungus parasitizing an alga

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AIR POLLUTION SENSITIVITY

▢ Sulphur Dioxide:

❖ Effect: Lichens are highly sensitive to \(SO_2\) pollution

❖ Mechanism:

\(Mg^{2+}\) in chlorophyll is replaced
A toxic substance called phycophytin is formed
The lichen dies

▢ Distribution: Lichens generally do not grow near large cities, industrial areas or places with heavy smoke and air pollution.

▢ Indicator Role: Useful biological indicators of air pollution

▢ Radioactivity: Lichens are efficient absorbers and accumulators of radioactive substances

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CLASSIFICATION

▢ Based on Habitat:

Table 1: Habitat-Based Classification

Type	Habitat
Saxicolous	Grow on rocks or stones
Terricolous	Grow on soil
Corticolous	Grow on the bark of trees
Lignicolous	Grow on wood

▢ Based on Fungal Partner:

❖ Ascolichens:

◉ Fungal Partner: Ascomycetes

◉ Occurrence: Majority of lichens

◉ Algal Partner: Usually green algae; rarely blue-green algae

◉ Types:

◈ Gymnocarpae:

■ Fruiting Body: Apothecium

■ Shape: Cup-shaped

◈ Pyrenocarpae:

■ Fruiting Body: Perithecium

■ Shape: Flask-shaped

❖ Basidiolichens:

◉ Fungal Partner: Basidiomycetes

◉ Algal Partner: Usually blue-green algae

❖ Partner Distribution:

Table 1: Algal Partners in Lichens

Algal Group	Approximate Frequency
Green algae or Chlorophyceae	Approximately 80%
Blue-green algae or Cyanophyceae	Approximately 20%

Most lichens are associations between green algae and Ascomycetes.

◉ Important Green Algal Partners:

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Trebouxia
•
Cladophora
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Pleurococcus

◉ Important Blue-Green Algal Partners:

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Anabaena
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Nostoc
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Scytonema

▢ Based on Thallus Structure and Attachment:

Table 1: Thallus-Based Classification

Type	Characteristics	Examples
Crustose	◉ Features: • Crust-like thallus • Entire thallus firmly attached to the substratum • Cannot be removed without damaging the thallus	• Graphis • Lecanora • Dermatocarpon • Rhizocarpon
Foliose	◉ Features: • Leaf-like or lobed thallus • Attached to substratum by rhizines • Partly free from substratum	• Parmelia • Peltigera • Physcia
Fruticose	◉ Features: • Shrubby or bushy thallus • Highly branched • Attached to substratum at one point by a disc	• Usnea • Cladonia • Cetraria

❖ Crustose Lichens:

◉ Examples:

◈ Graphis: Crustose lichen

◈ Lecanora: Crustose lichen

◈ Dermatocarpon: Crustose lichen

◈ Rhizocarpon: Crustose lichen

❖ Foliose Lichens:

◉ Parmelia:

◈ Common Name: Rock flower

◈ Uses:

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Used as curry powder
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Traditionally used in the treatment of epilepsy

◉ Peltigera:

◈ Common Name: Dog lichen

◈ Use: Traditionally used as medicine for hydrophobia

◉ Physcia:

Foliose lichen

❖ Fruticose Lichens:

◉ Usnea:

◈ Common Name: Old man's beard

◈ Importance:

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Source of usnic acid
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Usnic acid is a broad-spectrum antibiotic
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Dry thalli may contribute to the spread of forest fire during hot seasons

◉ Cladonia:

◈ Common Name: Reindeer moss

◈ Importance:

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Serves as food for reindeer in Arctic regions
•
Traditionally used in the treatment of whooping cough

◉ Cetraria:

◈ Common Name: Iceland moss

◈ Importance:

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Edible in Iceland
•
Traditionally used as medicine for diabetes

❖ Filamentous Lichen: Racodium

▢ Based on Algal Partner:

❖ Chlorophycophilous Lichens: Algal partner belongs to Chlorophyceae or green algae

❖ Cyanophycophilous Lichens: Algal partner belongs to Cyanophyceae or blue-green algae

▢ Based on Internal Anatomy:

Table 1: Anatomical Classification of Lichen Thallus

Type	Distribution of Partners	Occurrence	Examples
Homoiomerous	Algal and fungal components are uniformly distributed throughout the thallus	Rare	Commonly represented by simple crustose forms
Heteromerous	Thallus differentiated into distinct fungal and algal zones	Most lichens	• Foliose lichens • Fruticose lichens

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THALLUS STRUCTURE

▢ General Organization: Lichen thallus is formed by closely associated algal cells and fungal hyphae.

▢ Typical Heteromerous Thallus:

❖ Upper Cortex: Compact fungal hyphae forming the upper protective layer

❖ Algal Zone: Layer containing algal cells surrounded by fungal hyphae

❖ Medulla: Loosely arranged fungal hyphae

❖ Lower Cortex: Compact fungal layer on the lower surface

❖ Rhizines: Root-like fungal structures attaching the thallus to the substratum

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SPECIAL STRUCTURES

Table 1: Special Structures Associated with Lichen Thallus

Structure	Location or Nature	Function
Breathing Pores	Loosely arranged areas in the upper cortex	Gaseous exchange
Cyphellae	Loosely arranged areas or depressions in the lower cortex	• Gaseous exchange • Analogous to stomata of higher plants
Cephalodia	Special swellings or outgrowths of the thallus	Retention of moisture
Isidia	Corticated outgrowths of the lichen thallus	• Increase surface area • Vegetative reproduction
Soralium	Localized powdery patch on the thallus	Produces soredia

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REPRODUCTION

▢ Vegetative Reproduction:

❖ Fragmentation: Each detached fragment containing both partners may develop into a new thallus

❖ Isidia:

◉ Definition: Small outgrowths of the lichen thallus containing both algal and fungal components

◉ Process: After detachment, each isidium may form a new lichen thallus

◉ Functions:

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Vegetative reproduction
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Increase in photosynthetic surface area

❖ Soredia:

◉ Definition: Small granular propagules composed of one or more algal cells surrounded by fungal hyphae

◉ Site of Production: Produced in large numbers in a patch called a soralium

◉ Process:

Soredia develop in the soralium
They detach from the parent thallus
They are dispersed
Each soredium regenerates into a new lichen thallus

▢ Asexual Reproduction:

❖ Spores:

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Pycnidiospores
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Pycniospores

❖ Pycnidium: Flask-shaped structure in which pycniospores are produced

❖ Ostiole: Pore through which the pycnidium opens to the exterior

▢ Sexual Reproduction:

❖ Responsible Partner: Fungal partner only

❖ Role of Algal Partner: No direct role in sexual reproduction

❖ Male Reproductive Structure:

◉ Name: Spermatogonium

◉ Product: Numerous non-motile male cells called spermatia

❖ Female Reproductive Structure:

◉ Name: Carpogonium

◉ Parts:

◈ Ascogonium: Lower coiled portion

◈ Trichogyne: Upper elongated receptive portion projecting through the upper cortex

❖ Fertilization:

Spermatium reaches and attaches to the trichogyne
Male nucleus passes into the carpogonium
Fertilization occurs
Ascogenous hyphae develop
A fungal fruiting body is formed

❖ Fruiting Bodies:

Table 1: Fruiting Bodies in Lichens

Type	Shape
Apothecium	Cup-shaped or disc-shaped
Perithecium	Flask-shaped

Q1.

A group of algal cells surrounded or imprisoned by fungal mycelium and serving in vegetative multiplication of a lichen is called:

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ECONOMIC IMPORTANCE

▢ Food and Fodder:

❖ Nutritional Feature: Many lichens are rich in carbohydrates

❖ Examples:

◉ Cladonia: Food for reindeer

◉ Cetraria islandica: Edible Iceland moss

▢ Dyes and Indicators:

❖ Litmus:

◉ Source: Roccella tinctoria

◉ Use: Acid-base indicator

▢ Medicinal Importance:

❖ Lichenin: Substance associated with medicinal properties of some lichens

Table 1: Medicinal Uses of Lichens

Lichen	Traditional Use or Importance
Usnea	Source of broad-spectrum antibiotic usnic acid
Lobaria	• Traditionally used for tuberculosis and lung diseases • Used in tanning • Used in brewing • Used in perfumery
Xanthoria	Traditionally used for jaundice
Parmelia	Traditionally used for epilepsy
Peltigera	Traditionally used for hydrophobia
Cladonia	Traditionally used for whooping cough
Cetraria	Traditionally used for diabetes

▢ Perfumery and Cosmetics:

❖ Uses:

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Soaps
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Cosmetics
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Perfumes

❖ Sweet-Scented Lichens:

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Evernia
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Ramalina

▢ Ecological Importance:

❖ Pioneer Organisms: Lichens are pioneers of vegetation on bare rocks and initiate lithosere succession

❖ Rock Weathering:

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Secrete acids that dissolve rock minerals
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Trap dust and organic matter
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Promote soil formation
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Prepare the habitat for mosses and higher plants

❖ Xerosere:

◉ Definition: Ecological succession beginning in a dry habitat

◉ Pioneer Stage: Crustose lichens

◉ Sequence: \(\text{Crustose lichens} \rightarrow \text{Foliose lichens} \rightarrow \text{Moss stage} \rightarrow \text{Herb stage} \rightarrow \text{Shrub stage} \rightarrow \text{Tree or climax community}\)

❖ Pollution Monitoring: Used as biological indicators of air pollution, particularly sulphur dioxide pollution

❖ Radioactive Monitoring: Accumulate radioactive substances and may be used for environmental monitoring

▢ Poisonous Lichens:

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Cetraria juniperina
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Letharia vulpina — wolf moss

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IMPORTANT EXAMPLES

Table 1: Important Lichens and Their Significance

Lichen	Type or Common Name	Importance
Parmelia	Foliose; rock flower	• Curry powder • Traditional remedy for epilepsy
Peltigera	Foliose; dog lichen	Traditional remedy for hydrophobia
Usnea	Fruticose; old man's beard	Source of usnic acid
Cladonia	Fruticose; reindeer moss	• Food for reindeer • Traditional remedy for whooping cough
Cetraria	Fruticose; Iceland moss	• Edible • Traditional remedy for diabetes
Roccella tinctoria	Dye-producing lichen	Source of litmus
Lobaria	Lungwort	• Traditional treatment of lung diseases • Tanning • Brewing • Perfumery
Xanthoria	Yellow-coloured lichen	Traditional remedy for jaundice
Evernia	Sweet-scented lichen	Perfumes, cosmetics and soaps
Ramalina	Sweet-scented lichen	Perfumes, cosmetics and soaps
Racodium	Filamentous lichen	Example of filamentous thallus

High-Yield Points

❖ Phycobiont: Algal component

❖ Mycobiont: Fungal component

❖ Most Common Association: Green alga + Ascomycete fungus

❖ Air-Pollution Indicator: Lichens are especially sensitive to \(SO_2\)

❖ Pioneer of Lithosere: Crustose lichens

❖ Vegetative Propagule: Soredium = algal cells surrounded by fungal hyphae

❖ Broad-Spectrum Antibiotic: Usnic acid from Usnea

❖ Litmus Source: Roccella tinctoria

❖ Reindeer Food: Cladonia

❖ Iceland Moss: Cetraria

❖ Dog Lichen: Peltigera

❖ Rock Flower: Parmelia

❖ Old Man's Beard: Usnea

Q1.

Lichens are ecologically important because [MOE 2061]

📅MOE 2061

Q2.

The mode of life of lichen is: [MOE 2058]

📅MOE 2058

Q3.

Which of the following is a composite dual organism? [MOE 2063]

📅MOE 2063

Q4.

Usnea is a [IOM 2004]

📅IOM 2004

Q5.

Which is wrong about lichens? [BPKIHS 2002]

📅BPKIHS 2002

Q6.

Organism which are indicator of SO2 pollution in air are [IE 2003)

📅IE 2003)

Q7.

Lichens are indicator of: [BPKIHS - 2010)

📅BPKIHS - 2010)

Q8.

Which one of the following is a fructose lichen? [MOE 2013)

📅MOE 2013)

Q9.

Lichen is association of [MOE 2010)

📅MOE 2010)

26Lichen

Table 1: Habitat-Based Classification

Table 1: Algal Partners in Lichens

Table 1: Thallus-Based Classification

Table 1: Anatomical Classification of Lichen Thallus

Table 1: Special Structures Associated with Lichen Thallus

Table 1: Fruiting Bodies in Lichens

Table 1: Medicinal Uses of Lichens

Table 1: Important Lichens and Their Significance

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