Classification of Chlorophyceae (Green Algae)

The class Chlorophyceae is divided into the following orders:

Order. 1. Volvocales:

The order Volvocales includes 60 genera and about 500 species.

Important characteristics:

1. They are commonly found in freshwater bodies. Some are grown in brackish water, marine water, and also on soil surfaces.
2. The plant body or thallus is unicellular or multicellular(many-celled) and the multicellular ones are colonial in habit.
3. Both unicellular and colonial members are motile(Having flagella), either throughout or some part of their life cycles.
4. They reproduce both sexually and asexually. Asexual reproduction takes place by zoospo­res, aplanospores, hypnospores, etc., and sex­ual reproduction takes place by isogamy, anisogamy, and oogamy.

Classification:

Fritsch (1935) divided the order Volvocales into 3 suborders and 7 families.

Order. Volvocales:

2. Sub order. Chlamydomonadineae
3. Sub order. Tetrasporineae
4. Sub order. Chlorodendrineae

Order. 2. Ulotrichales

Order Ulotricales includes 80 genera and about 430 species. Most of them are found in freshwater, while a few are marine (e.g., Ulva).

Important characteristics:

1. They are commonly found in freshwater bodies(e.g., Ulothrix) or on soil, but a few are marine (e.g., Ulva, Enteromorpha).
2. The plant body is commonly unbranched fila­ment like, but in Ulvaceae, it is parenchymatous or foliaceous.
3. Cells are uninucleate(single nucleus) and contain different types of chloro­plast  like C-shaped, pari­etal, axial, etc.
4. Each chloroplast contains/have one or more pyrenoids.
5. Asexual reproduction occurs through biflagellate zoospores or Quadri-flagellate zoospores, aplanospore, and akinetes.
6. Sexual reproduction takes place by the gametic union and may be isogamous, anisogamous, or oogamous type.

Classification:

Fritsch (1935) divided the order Ulotrichales into 3 suborders and 6 families.

Order. Ulotrichales

Sub order. Ulotrichineae

Family. Ulotrichaceae

• Microsporaceae
• Cylindrocapsaceae
• Ulvaceae

Sub order. Prasiolineae

Family. Prasiolaceae

Sub order. Sphaeropleineae

Family. Sphaeropleaceae

Family. Ulotrichaceae

Important characteristics of Ulotrichaceae

1. The plant body is an unbranched filament.
2. Cells of the filament are uninucleate(One Nucleus).
3. Cells have single girdle-shaped, parietal chloroplasts.
4. Sexual reproduction is isogamous and takes place by the union of biflagellated gametes

Order. 3. Chaetophorales:

Chaetophorales are plants with hair or setae

Important characteristics:

1. Members of Chaetophorales are generally found in freshwater.
2. The plant body is filamentous and shows promi­nent heterotrichous(prostrate  +Erect system) habit; however, in Coleochaete, the prostrate system(creeping) is well- developed and in Microthamnion the erect system is well-developed.
3. Some members have setae (Coleochaete) or hairs (Stigeoclonium) of different types. The hairs may be in the form of single elon­gated cells or rows of fine and elongated cells.
4. The cells contain a parietal-shaped chloroplast with many pyrenoids (starch-containing bodies).
5. The erect system bears/contains reproductive structures.
6. Vegetative reproduction takes place/done by frag­mentation.
7. Asexual reproduction occurs through biflagellate zoospores or quadriflagellate zoospores, aplanospores, or akinetes.
8. Sexual reproduction is commonly isogamous (Fritschiella, Stigeoclonium), anisogamy (Aphanochaete), and oogamy (Coleochaete) are found occasionally/Rarely.

Fritsch (1935) classified this order into 5 families.

These are Chaetophoraceae, Trentepohliaceae, Coleochaetaceae, Chaetosphaeridiaceae, and Pleurococcaceae.

Family. Coleochaetaceae:

Important characteristics:

1. Plant bodies possess a typical heterotrichous(erect + prostrate) habit. Generally, the projecting(upward) system is dominant and looks like a disc.
2. Cells are uninucleate(one Nucleus) with a single lamellate parietal chloroplast with one or two pyrenoids(Starch containing bodies).
3. All or some cells bear/having/containing a single long sheathed bristle or seta.
4. The sheath is present in the form of a basal cylinder of mucilage layer.
5. The growth always takes place through the apical region.
6. Asexual reproduction takes place by means of biflagellated zoospores.
7. Sexual reproduction is an oogamous type.

Order. 4. Oedogoniales

Important characteristics:

1. Most of the members grow in fresh water. The order is represented by only three genera, Oedogomium, Oedocladium, and Bulbochaete.
2. They are filamentous and the filaments may be branched (Oedocladium and Bulbo­chaete) or unbranched (Oedogomium).
3. The plant body is differentiated into the apical and basal regions.
4. It consists of cylindrical cells and the cells are longer than breadth.
5. Cells are uninucleated and have reticulate chloroplast with pyrenoids.
6. Cell division is elaborate and a cap is formed at the upper end of the daughter cell.
7. Asexual reproduction takes place by pyriform, multinucleate, and multiflagellate zoospores. Flagella are arranged in a ring around the beak-like anterior end.
8. Sexual reproduction is an advanced oogamous type.
9. Both androspores and antherozoids are multiflagellate.
10. Male gametes are similar to zoospores but smaller in size.
11. Heterothallic or dioecious species are of two types: macrandrous (where male and female filaments are of normal size) and nannandrous type (where the male is very small i.e., dwarf male or nannandrium and the female one is of normal size.

Classification:

According to Fritsch (1935), the order Oedogoniales contains only one family Oedogoniaceae. The family has only three genera: Oedogomium, Oedocladium, and Bulbochaete.

Order.5. Siphonales:

Important characteristics:

1. Most of the members of Siphonales are marine. A few members are freshwater. Some members grow as epiphytes or endophytes.
2. The thalloid plant body is variously branched, aseptate and multinucleate i.e., coenocytic.
3. Plant body may be simple vesicular type (Protosiphon) to much-branched filamentous type.
4. Numerous small and discoid chromato- phores are arranged peripherally inside the thallus.
5. Nuclei are present in the inner layer.
6. The characteristic pigments of this order are siphonin and siphonoxanthin.
7. Presence of siphon-like central vacuole throughout the plant body, which remains filled with sap. The cytoplasm is present between the outer wall and the vacuole. The order is named “Siphonales” because of the presence of a siphon-like vacuole.
8. The plant reproduces by all three means vegetative, asexual, and sexual. Vegetative reproduction takes place by fragmentation, asexual reproduction by multiflagellate zoospore, aplanospore or hypnospore, and sexual reproduction by oogamy. Rarely do they perform iso- and anisogamy.

Classification:

Fritsch (1935) divided the order Siphonales into 9 families.

These are:

1. Protosiphonaceae
2. Caulerpaceae
3. Dasycladaceae
4. Derbesiaceae
5. Codiaceae
6. Valoniaceae
7. Chaetosiphonaceae
8. Phyllosiphonaceae
9. Vaucheriaceae.

This classification is also followed by M. O. P. lyenger (1951)

Order.6. Charales 

Important characteristics:

1. Members of this order are distributed throughout the world.
2. Commonly they are found in freshwater with a muddy or sandy bottom and also in water flowing over limestone.
3. Plants are macroscopic, much branched, and erect and commonly up to 30 cm in length.
4. The plants are differentiated into nodes and internodes. Some of the nodes bear bran­ches of unlimited growth, those are again divided into nodes and internodes. Each node of the main axis and branch of unlimi­ted growth bear a number of branches of limited growth.
5. Cells are very long, uninucleated, and contain many discoid chloroplasts.
6. Most of the species show cortication in the internodes. The cortex consists of a vertically elongated row of cells.
7. Sexual reproduction is a highly advanced, oogamous type.
8. The male and female reproductive bodies are globule and nucule, respectively. Globule develops many antherozoids and nucule contains only one egg.
9. A zygote is produced after sexual reproduc­tion. It shows very elaborate post-fertilization changes. During germination, the zygote undergoes meiosis and gradually it forms the plant body.

Classification:

Fritsch (1935) placed the order Charales under the class Chlorophyceae includes only one family the Characeae having 2 subfamilies: 1. Nitelleae and 2. Chareae.

Bold and Wynne (1978) placed the order Charales alone under the only class Charophyceae, under the division Charophyta. The order Charales includes only one family Characeae.Divn. Charophyta: Class. Charophyceae.

1. C. Bold and M. J. Wynne (1978) in their classification took out Chara along with some other genera like Tolypella, Nitella, Nitellopsis, Protochara, Lamprothamnium, and Lychnotham- nus from Chlorophyceae and placed them in a separate Division Charophyta. The Charophyta consists of a single class Charophyceae; the order Charales and the family Characeae.Chlorophyceae

Important characteristics of Characeae:

1. The division Charophyta includes the members of green algae, commonly known as stoneworts.
2. The plant body shows much elaboration of vegetative structures encrusted with calcium carbonate.
3. The plant body is erect and consists of elon­gated, jointed, commonly green main axis bearing branches, differentiated into nodes and internodes.
4. Each node bears a whorl of lateral branchlets.
5. Asexual reproduction is absent.
6. Sexual reproduction is of oogamous type.
7. Antheridia (globule) and oogonia (nucule) show more complexity and elaboration than other Chlorophycean members.
8. Motile cells are asymmetrical and two flagella are attached in the lateral position of an antherozoid.
9. Sex organs are so large that they can be visible to the naked eye.
10. Zygotes on germination form protonema (Chara, Nitella) from which vege­tative plants are developed.

.Order.7. Chlorococcales:

1. Unicellular or colonial,
2. non-motile in the vegetative condition,
3. reproduced by zoospores or aplanospore;
4. almost exclusive fresh water.

Examples:

• Hydrodictyon
• Pediastrum, etc.

Order.8. Cladophorales:

1. Simple or branched,
2. filamentous with cells containing two too many nuclei and usually with elaborate large chloroplasts;
3. mostly isogamous;
4. freshwater and marine.

Exam­ple: Cladophora.

Order.9. Conjugales:

1. Most are Unicellular or colonial (generally filamen­tous) with elaborate chloroplasts;
2. They Have motile gametes ;
3. Re­production takes place by vegetative cell division or by conjugation of amoeboid gametes;
4. exclusively freshwater.

Examples:

• Spirogyra,
• Zygnema,
• Cosmarium,
• Closterium,