3.2 Salient features of major plant groups under Cryptogams:
A. Division : Thallophyta
Members are mostly aquatic, few grow on other plants as epiphytes.
Some grow symbiotically and epizoic i.e. growing or living non-parasitically on the exterior of living organisms.
Aquatic algae grow in marine or fresh water.
Most of them are free living while some are symbiotic.
Plant body is thalloid i.e. undifferentiated into root, stem and leaves.
They may be small, unicellular, microscopic like Chlorella (nonmotile), Chlamydomonas (motile).
They can be multicellular, unbranched, filamentous like Spirogyra or branched, filamentous like Chara.
Sargassum, a huge macroscopic sea weed which measures more than 60 meters in length is also an alga.
The algal cell wall contains either polysacchrides like cellulose / glucose or a variety of proteins or both.
Reserve food is in the form of starch and its other forms.
Reprocuction takes place by vegetative asexual and sexual way.
The life cycle shows phenomenon of alternation of generation, dominant haploid and reduced diploid phases.
Algae are classified as per its pigments like chlorophyll, Xanthophylls and phycobilin.
a. Chlorophyceae (green algae) :
These are mostly fresh water (few brackish water and marine).
Plant body is unicellular, colonial, filamentous.
Cell wall contains cellulose.
Chloroplasts are of various shapes like discoid, plate-like, reticulate, cup-shaped, ribbon-shaped or spiral with chlorophyll a and b.
The stored food is in the form of starch.
Pyrenoids are located on Chloroplast.
Members are rich in protein, so used as food; used even by space travellers, e.g. Chlorella, Chlamydomonas, Spirogyra, Chara, Volvox, Ulothrix etc.
b. Phaeophyceae (Brown algae):
Plant body : Mostly marine, rarely fresh water. Simple branched / filamentous (e.g. Ectocarpus) / profusely branched (Petalonia).
Cell wall has cellulose, fucans and algin.
Photosynthetic pigments like chlorophyll-a, chlorophyll-c and fucoxanthin are present.
Mannitol, laminarin and starch are stored food materials.
Body is usually differentiated into holdfast, stalk called stipe and leaf-like photosynthetic organ called frond.
Many species of marine algae are used as food. e.g. Porphyra,Laminaria,Sargassum.
Some species are used for production of hydrocolloids, e.g. Ectocarpus, Fucus, etc.
c. Rhodophyceae (Red algae) :
Plant body These are found in marine as well as fresh water on the surface, deep sea and brackish water.
Plant body is thalloid.
Cells contain chlorophyll a, chlorophyll d and phycoerythrin.
Cell wall is made up of cellulose and pectin glued with other carbohydrates.
Stored food is in the form of Floridean starch.
Commercially important agar-agar which is used as solidifying agent in tissue culture medium is obtained from red algae.
e.g. Chondrus, Batrachospermum Porphyra,Gelidium,Gracillaria, Polysiphonia etc.
Can you Tell ?
