August W. Eichler

German botanist

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ALGAE

Algae are simple, chlorophyll bearing photosynthetic non vascular

plants (Thallophytes).

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Salient Features

• Body is relatively simple, unicellular or multicellular thallus, not

differentiated into roots, stem and leaves

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• Algal cells – Prokaryotic or Eukaryotic

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• Cells are covered with a rigid cell wall

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• Cells contain plastids and three classes of pigments.• Chlorophyll

• Carotenoids

• Phycobilin

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• The reserve food includes mostly starch and oils.

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• Absence of vascular and mechanical tissue. The entire thallus is made

up of parenchyma cells

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Reproduction

• Vegetative method – New identical individuals are produced from

vegetative parts of the algae. No change in protoplasm.

• Asexual method – New identical progenies are produced by the means of

special structures formed. Involves changes in protoplasm

• Sexual method – Progenies are formed as a result of fusion of gametes.

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• Sex organs are usually unicellular and non – jacketed.

• Multicellular sex organs are rare and in them each cell is fertile

without jacket of sterile cells.

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• Embryo is not formed after gametic fusion

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• In most genera the only diploid stage in the life cycle is the zygote,

which immediately undergoes meiosis.

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• Sporophytic and gametophytic generations, when present in the life

cycle, are independent.

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Habit- Plant body

• Thallus organization

• Unicellular forms

Motile - Chlamydomonas Non motile - Chlorella14

Multicellular forms

1) Colonial types – The cells are grouped into aggregations called colonies

Motile - Volvox Non motile - Pediastrum

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2) Filamentous forms – Multicellular branched or unbranched

Unbranched filamentous - Spirogyra Branched filamentous - Chladophora

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Heterotrichous habits

• Heterotrichy means producing two types of branches. (a) Prostrate

branches (prostrate system) (b) Erect branches (erect system).

Ectocarpus 17

Siphonaceous habit

• Tube like plant body

Eg : Vaucheria

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Smallest and largest ?The genus Micromonas is comprised of small single-celled micro-algae

Macrocystis pyrifera, commonly known as giant kelp or giant bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus Macrocystis

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Habitat- The place where they live

• According to habitat, the algae may be classified as follows:

• Aquatic algae

• Terrestrial algae

• Aerophytes

• Cryophytes

• Thermophytes

• Algae of unusual habitats

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Aquatic algae

• Majority of the algal genera are aquatic

• Found usually in ponds, pools, tanks, ditches, streams or slow running

rivers.

• Fresh water algal forms like Chlamydomonas, Volvox are found in

stagnant water where as Chladophora, Oedogonium occur in slow

running waterbodies.

• Marine algae are found in sea are commonly called as sea weeds.21

• The free floating and free swimming microscopic algal forms together

with other similar organism constitute the planktons of water bodies.

• Euplanktons – Never attached

• Tychoplanktons – in the beginning may be attached, but later they get

detached.

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Terrestrial algae

• Algal genera found on or beneath the moist soil are called terrestrial

algae.

• Eg : Fritschiella, Nostoc

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Aerophytes

• Algal forms adapted for aerial mode of life and occur on tree trunks,

moist walls, rocks etc.

Eg : Trentepholia

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Cryophytes

• Algae found on low temperature or snow.

Red snow – Haematococcus nivalis25

Thermophytes

• Algal genera occurring in hot springs at quite high temperature.

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Algae of unusual habitats

1. Halophytic algae – Algae found in saline water ( High percentage of

salts) Eg: Dunaliella

2. Lithophytic algae – Algae grow on rocks or rocky surface. Eg : Rivularia

Dunaliella Rivularia 27

3. Epiphytic algae – Algal forms grow on other aquatic plants – Oedogonium

4. Epizoic algae – Algal forms grow on animals – Chladophora

5. Endozoic algae – Algal forms found inside aquatic animal – Zoochlorella

6. Parasitic algae – Algal forms found on host organism which gets its

nourishment from host – Eg : Celphaleurose virescence – red rust of tea

Oedogonium CelphaleuroseZoochlorellaChladophora 28

7. Symbiotic algae – Algae lives in mutualistic relationships

- Eg : Nostoc, Anabaena, Lichenized algae

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Algal pigments

• Pigments are chemical substances which can impart their

characteristic colour. The main pigments in algae include

1. Chlorophylls

2. Carotenoids – Carotenes and xanthophylls

3. Phycobilins – Phycoerythrin, Phycocyanin

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Pyrenoid

• The algal plasmids often contain a proteinaceous body called pyrenoid.

• Very common in green algae

• Pyrenoids store starch over them as plates

• Usually a cell contains either one or more of these bodies.

• Pyrenoids are completely absent in BGA.

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Reproduction

• Vegetative reproduction• Cell division

• Fragmentation

• Splitting of colonies

• Hormogones

• Budding

• Tubers

• Amylum stars

• Stolons

• Adventitious branches

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• Cell division – Seen in unicellular forms Eg: Diatoms

• Fragmentation – Due to physical disturbance, thallus gets broken into bits.

Each bit is capable of independent living by successive cell division and

enlargement. Eg – Filamentous forms like Spirogyra.

• Splitting of colonies – At maturity, a single colony gets divided into two

and later the doughter colonies attain their maximum size. Eg:

Aphanotheca

• Hormogones – In cyanobacteria, plant body is filamentous and is called

trichome. The trichome gets separated into smaller units called

hormogones. Each hormogone becomes an adult filament by further cell

division. 33

• Budding – In some algae the plant body develops buds which further

constrict and separate to form new algae. Eg : Protosiphon.

• Tubers – Starch filled globular bodies produced from rhizhoids and

nodes which later detach from the plant. Eg : Chara

• Amylum stars – Star shaped vegetative propagule filled with amylum

starch. They also get detached. Grow out to form a new algae. Eg:

Chara34

• Stolons – Special outgrowths or rhizoids grow from the filament. They

produce new plants at distance. Eg : Chladophora

• Adventitious branches – Special branches formed from the thallus.

They separate and form independent plants. Eg : Fucus

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Asexual reproduction

• Asexual reproduction is a process in which the protoplast (or protoplasts)

is released from the cell.

• This protoplast germinates into a new plant.

• It takes place by the formation of various types of spores like zoospore,

synzoospore, aplanospore, hypnospore, autospore, tetraspore, etc.

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Zoospore

• Flagellated, asexual reproductive bodies, usually each having an

eyespot, e.g. Chlamydomonas, Ulothrix and Cladophora.

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Synzoospore

• multinucleate and multiflagellated zoospore.

• It is also called compound zoospore.

• Eg : Vaucheria

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Aplanospore

• Aplanospore is a non-motile, thin-walled zoospore formed by the

cleavage of protoplast within a cell. Eg : Chlamydomonas

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Hypnospore

• Hypnospore is a thick-walled aplanospore eg: Vaucheria.

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Autospores

• Autospores are the replicas of the parent cell and formed by the cell

division., e.g. Chlorella

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Tetraspore

• Tetraspores are haploid, thin-walled, nonmotile spores formed after

reduction division in diploid tetrasporangia of many Red algae and

also in some Brown algae (e.g. Dictyota)

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Sexual reproduction

• Takes place by the union of cytoplasm and nuclear material of two

gametes of two organisms of the same species.

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Classification of algae

• Classification proposed by A.W. EICHLER (1886)

• Eichler recognized following five groups in algae:

1. Cyanophyceae

2. Diatomeae

3. Chlorophyceae

4. Phaeophyceae

5. Rhodophyceae

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Classification proposed by F.E. FRITSCH

• In the system proposed by Fritsch, algae are divided into following 11 classes.

1. Chlorophyceae

2. Xanthophyceae

3. Chrysophyceae

4. Bacillariophyceae

5. Cryptophyceae

6. Dinophyceae

7. Chloromonadineae

8. Euglenineae

9. Phaeophyceae

10. Rhodophyceae

11. Myxophyceae 45