Fritsch classified algae on the bases of phylogeny, affinities, and interrelations. Characters like structure of the plant body, nature of the plant body, nature of the pigments and reserve food materials, methods of reproduction, occurrence are few basic consideration in his classification. He has considered algae as one group equivalent to a division and has divided living forms of this group into 11 classes as fallows.
1) Chlorophyceae
Occurrence- Fresh water but few are marine
Pigments- The chief pigments are chlorophyll a and b and two yellow pigments. Thus chromatophores are grass-green in color.
Reserve food material- Starch
Structure- The plants are unicellular motile to heterotriches filaments. Cell wall consists of cellulose. Pyrenoids are commonly surrounded by starch sheath. Motile cell have equal flagella.
Reproduction- Sexual
2) Xanthophyceae
Occurrence- Fresh water few are marine
Pigments- Chromatophores are yellow-green. Yellow xanthophyll is found abundantly.
Reserve food material- Oil
Structure- Unicellular to filamentous. Cell wall is made up pectic compounds and motile cells have two unequal flagella.
Reproduction- Sexual
3) Chrysophyceae
Occurrence- Cold fresh water some are marine
Pigments- Phycochrysin, Chromatophores are brown or orange colored.
Reserve food material- Fat & Leucosin
Structure- Unicellular motile to filamentous. Flagella are unequal.
Reproduction- Sexual
4) Bacillariophyceae
Occurrence- Fresh water, marine water and terrestrial habitats.
Pigments- Chromatophores are yellow or golden brown.
Reserve food material- Fat
Structure- Unicellular or colonial. cell wall is partly made up of silica and partly made up of pectin and it is ornamented.
Reproduction- Sexual
5) Cryptophyceae
Occurrence- Fresh water and marine habitat.
Pigments- Chromatophores are shade of brown
Reserve food material- Carbohydrates
Structure- Plant body have motile cells and most advanced forms are coccoid.
Reproduction- Isogamous
Structure- Contain motile cells, flagella are slightly unequal.
6) Dinophyceae
Occurrence- Occur widely as sea water planktons. Few are fresh water form.
Pigments- Chromatophores are dark yellow, brown etc.
Reserve food material- Starch and Oil.
Structure- Unicellular motile to branched filamentous.
Reproduction- Sexual
7) Chloromonadineae
Occurrence- Fresh water
Pigments- Xanthophyll. Chromatophores are bright green in color.
Reserve food material- Oil
Structure- Plants are motile and flagellate
Reproduction- Sexual
8) Euglenineae
Occurrence- Fresh water forms.
Pigments- Chromatophores are pure green.
Reserve food material- Polysaccharide, paramylon.
Structure- The plants are motile flagellate. Plants have complex vacuolar system and a large and prominent nucleus.
Reproduction- Sexual
9) Phaeophyceae
Occurrence- All forms
Pigments- Fucoxanthin
Reserve food material- Alcohol, polysaccharide and fats.
Structure- Plants are filamentous to bulky parenchymatous form.
Reproduction- Sexual, alternation of generation type of lifecycle.
10) Rhodophyceae
Occurrence- Fresh water and marine
Pigments- Phycoerythrin and phycocyanin
Reserve food material- Starch and Polysaccharide
Structure- Simple filamentous. Except few forms, cells show protoplasmic connections.
Reproduction- Sexual. After sexual reproduction some special spores are formed.
11) Myxophyceae
Occurrence- Sea, fresh water and moist soil.
Pigments- Chlorophyll, carotenes, xanthophylls, phycocyanin and phycoerythrin.
Reserve food material- Sugar and Glycogen
Structure- Simple to filamentous which shows false and true branching. Cells have rudimentary nucleus.
Reproduction- No sexual reproduction.