Biology Today — December 2017

Algae of unusual habitats

• Halophytic algae - Occur in saline sea water and salt lakes and can withstand high concentration of salts, e.g.,
  Chlamydomonas ehrenbergii, Stephanoptera.


• Epiphytic algae - Grow on larger algae, bryophytes and angiosperms, e.g., Oedogonium and Microspora are found
  attached to larger species of Vaucheria, Cladophora and Rhizoclonium.


• Epizoic algae - Grow on animals such as snails, fishes and tortoise, e.g., Cladophora crispata (epizoic on snail).


• Endozoic algae - Occur in tissues of animals, e.g., Zoochlorella in Hydra viridis.


• Cryophytic algae - Grow on ice or snow and impart attractive colours to snow covered mountains, e.g., Haematococcus nivalis
  imparts red colour to alpine and arctic mountains while Chlamydomonas yellowstonensis and Mesotaenium species are
  responsible for green snow in Europe.


• Parasitic algae - Grow as parasites on many plants and animals, e.g., Cephaleuros virescens causes red rust in tea and
  coffee plantations.


• Thermophytes - Occur in hot water springs (50-70°C temperature) as are able to survive high temperatures due to absence
  of well organised nucleus, e.g., Oscillatoria brevis, Heterohormogonium sp.

Classification of Algae

• Based upon phylogeny, affinities and interrelationships, algae is classified into various classes by Dr. F. E. Fritsch. However,
  according to Whittaker’s system of classification, algae are mainly divided into three classes: Chlorophyceae, Phaeophyceae
  and Rhodophyceae.
  Table: Characteristics of different classes of algae
  Classes Structure Occurrence Major
  pigments

Reserve

food

material

Reproduction

Vegeta-

tive

Asexual Sexual

Chlorophy-

ceae, (Green

algae)

e.g., Spiro-

gyra, Ulothrix

Unicellular, colonial,

coenobial, filamentous,

siphonaceous. Cell wall

cellulosic and pectic,

pyrenoid single or

compound, embedded.

Motile cells with 2-

equal flagella.

Mostly fresh-

water, a

few marine.

A marked

tendency

towards

terrestrial

habitat.

Chl. a and b,

carotenes and

xanthophyll.

True

starch

and

sugar.

Fragmen-

tation or

fission.

Zoospores. Isoga-

mous to

advanced

oogamous.

Phaeophy-

ceae

(Brown algae)

e.g., Fucus,

Sargassum

Filamentous branched,

usually heterotrichous,

outer layer of cell wall

composed of alginic

and fucinic acids and

inner layer is cellulosic,

motile cells with 2 lateral

flagella, pyrenoid single,

stalked or projected.

Mostly marine. Chl. a and c,

fucoxanthin,

flavoxanthin,

b-carotenes.

Lami-

narin,

mannitol.

Fragmenta-

tion or

adventi-

tious

branching.

Zoospores,

aplano-

spores, etc.

Isogamous

to

oogamous.

Rhodophy-

ceae

(Red

algae) e.g.,

Polysiphonia,

Porphyra

Unicellular,

filamentous or

pseudoparenchymatous,

cell wall cellulosic and

pectic, motile cells not

known, pyrenoids simple

or compound, embedded

sometimes stalked.

Mostly marine. Chl. a and d,

phycoerythrins,

phycocyanin,

allophycocyanin,

carotenoids.

Floridean

starch.

Fragmenta-

tion.

Mono-

spores,

carpo-

spores,

etc.

Advanced

oogamous

type.