Classification of Algae (Fritsch's System 1935)

Algae are chlorophyll bearing thallophytes in which the sex organs are either unicellular or multicellular and not protected by sterile envelope. They are included under thal-lophytes as they have no roots, stem and leaves. The impor-tant features of algae are

1. Algae are primitive aquatic plants.

2. The plant body is a unicellular or multicellular thal-lus. Roots, stem and leaves are absent.

3. Algae are photosynthetic.

4. They may be prokaryotic or eukaryotic.

5. Starch is the common reserve food.

6. Algae reproduce by vegetative, asexual and sexual methods.

7. The sex organs are naked.

8. The sexual reproduction may be isogamous or anisogamous or oogamous type.

9. Most species are haploid.

The International Code of Botanical Nomenclature recommended certain suffixes for use in the classifica-tion of algae in order to avoid confusions in different levels

of classification. According to this code, the name of divi-sions should end in -phyta, the name of classes should end in-phyceae, the name of sub-classes should end in phycideae, the name of orders should end in -ales, the name of sub-orders should end in-inales, the name of families should end in -aceae, the name of genus should be the derivative of a Greek word, and the name of species should be the derivative of a Latin word.
Fritsch's System
F.E.Fritsch, the well-known algologist of the Great Britain, has published two volumes of books on Structure and reproduction of the algae in 1935 & 45, and discussed his own system of classification for algae in it. His system is the most comprehensive and authoritative account on al-gae even today.
His classification is based on pigmentation, details of flagella, storage food, presence or absence of true nucleus in cells, range of thallus structures, methods of reproduction and patterns of life cycle. Based on these characters, Fritsch divided algae into 11 classes. They are -
1. Chlorophyceae
7. Chloromonadineae
2. Xanthophyceae
8. Eugleninae
3. Chrysophyceae
9. Phaeophyceae
4. Bacillariophyceae
10. Rhodophyceae
5. Cryptophyceae
11. Myxophyceae
6. Dinophyceae
The different classes of algae are discussed as under:
1. Chlorophyceae
The members of Chlorophyceae are otherwise called green algae. This class includes 9 orders, namely Volvocales, Chlorococcales, Ulotrichales, Cladophorales, Chaetophorales, Oedogoniales, Conjugales, Siphonales and Charales. It includes 43 families with 360 genera and about 5700 species. The distinctive features of this class are given below:

1. These algae have grassy-green chromatophores which contain chlorophyll-a, chlorophyll -b, xanthophyll and caro. tenoids. All these pigments are approximately in the same proportion as in higher plants.

2. Their storage food are true starch and oil. The pyrenoids present in the chromatophores are surrounded by starch sheath.

3. The cell wall is rich in cellulose.

4. The cells exhibit 2 or 4 flagella which are equal in length, if motile.

5. The sexual reproduction may be isogamy, anisogamy or oogamy.

6. The thallus may be unicellular or multicellular. If multicellular, it may be filamentous or heterotrichous or siphonous or pseudo-parenchymatous.

7. Many species are haploid, but some are diploid.

8. They are more common in fresh water than in salt

water.

Chlamydomonas, Volvox, Chlorella, Oedogoniun, Caulerpa, Coleochaete, etc. are examples for green algae.

II. Phaeophyceae

The members of this class are otherwise called brown algae. Phaeophyceae includes 9 orders, namely Ectocarpales, Tilopteridales, Cutleriales, Sporochnales, Desmarestiales, Laminariales, Sphacelariales, Dictyotales and Fucales. There are 64 families with about 195 genera and 1000 species. The distinctive features of Phaeophyceae are as under:

1. The members of the class have brown coloured chro-matophores which contain excess of fucoxanthin and small proportion of chlorophyll -a and c, carotenoids.

. Food reserves are stored as alcohols, mannitol and laminarin. Rarely oils or fucosan granules.

3. In majority of the cases the cells contain fucosan vesicles.

4. The motile reproductive cells possess two lateral fla-gella, of which one faces upwards and the other faces down-wards.

5. The cell wall is made of cellulose, fucinic acid and alginic acid.

6. Sexual reproduction is very common, and it varies from isogamy to oogamy.

7. The zygote exhibits no resting period.

8. The thallus may be heterotrichous filaments or pseudo-parenchymatous filaments or true parenchymatous filaments.

9. Most of the members live in marine water as brown sea-weeds. A few live in fresh water.

Sargassum, Dictyota, Fucus, Macrocystis, etc. are com-mon representatives of Phaeophyceae.

III. Rhodophyceae

The members of this class are otherwise called red al-gae. Rhodophyceae includes 7 orders, namely Bangiales, Nemalionales, Gelidiales, Cryptonemiales, Gigartinales, Rhodymeniales and Ceramiales. There are 42 families with 400 genera and 2500 species. The distinctive features of Rhodophyceae are listed below:

1. The members of the class have red colour chromato-phores which contain excess of phycoerythrin and small amount of chlorophylls, carotenoids and xanthophylls.

2. Pyrenoids are often present in lower forms.

3. Food reserves are stored as floridean starch, galac-tan sulfate and floridosides.

4. Motile reproductive cells and flagellated members are not known.

5. The cell wall is made of polysaccharides and polyuronic acids.

6. Asexual and sexual reproductions are common. Sexual reproduction is mainly of oogamous type. After fer-tilization many branches of female sex organs fuse together and produce a cluster of carpospores. This phenomenon is called post fertilization change.

7. The thallus may be unicellular or multicellular. The multicellular forms may be either filamentous or pseudo-parenchymatous.

8. Many species live in marine water as red sea-weeds, but a few live in fresh water. Some are living on muddy soil.

Polysiphonia, Gracilaria, Batrachospermum, etc. are representatives of Rhodophyceae.

IV. Cyanophyceae (Myxophyceae)

The members of this class are otherwise called blue-green algae (BGA). This class includes 5 orders, namely Chroococcales, Chamaesiphonales, Pleurocarpales, Nostocales and Stigonematales. There are 18 families with about 150 genera and 1500 species in the class. The distinc-tive features of the class are listed below:

1. The members of this class are prokaryotic, and do not possess membrane bound cell organelles.

2. Chromatophores and pyrenoids are absent.

3. The colour of the cells is blue green due to the pres-ence of excess of phycocyanin and varying proportions of chlorophyll-a, ẞ- carotene, flavacine, myxoxanthophyll, myxoxanthin, oscillaxanthin and phycoerythrin in their pro-toplasm.

4. Reserve foods are stored as sugars (cyanophycean starch) and glycogen.

5. The cell wall consists of mucopolysaccharides and gelatinous envelope.

6. There is no sexual reproduction. Vegetative and asexual reproductions are common.

7. The thallus may be unicellular or colonial or filamen-

8. The members of the class are widely distributed in fresh water and moist soils. But some species live in sea water also.

The modern algologists have slightly modified the Fritsch's system and divided algae into 11 divisons. They are Cyanophyta, Chlorophyta, Charophyta, Xanthophyta, Chrysophyta, Bacillariophyta, Pyrrophyta, Cryptophyta, Euglenophyta, Phaeophyta and Rhodophyta.

Common representatives of Cyanophyceae are -Oscillatoria, Nostoc, Gloeocapsa, Scytonema, etc.