What is the basis of classification of algae?

Algae are classified into three main classes – Chlorophyceae, Phaeophyceae, and Rhodophyceae. These divisions are based on the following factors:

(a) Major photosynthetic pigments present

(b) Form of stored food 

(c) Cell wall composition 

(d) Number of flagella and position of insertion

Class I – Chlorophyceae 

Common name – Green algae

Major pigments – Chlorophylls a and b 

Stored food – Starch

Cell wall composition – Cellulose

Flagella number and position – 28; equal and apical

Class II – Phaeophyceae 

Common name– Brown algae

Major pigments – Chlorophylls a and c, and fucoxanthin

Stored food – Mannitol and laminarin

Cell wall composition – Cellulose and algin 

Flagella number and position – 2; unequal and lateral 

Class III – Rhodophyceae 

Common name – Red algae

Major pigments – Chlorophylls a and b, and phycoerythrin 

Stored food – Floridean starch 

Cell wall – Cellulose, pectin, and polysulphate esters 

Flagella number – Absent