Chlorophyta: Class, Important Features and Orders!
Class: Chlorophyceae:
The class Chlorophyceae is commonly called as green algae. Chlorophyceae is very large group of algae and is represented by about 429 genera and 6500 species. Chlorophyceae are mainly fresh water algae (about 90 percent species are fresh water and 10 percent marine). Fresh water forms are common in ponds, pools, lakes, ditches, water tanks, and in river and canals.
Majority of Volvocales, Chlorococcales are planktonic forms.
Many Chaetophorales e.g., Coleochaete, Protococcus. Trentepohlia are epiphytic algae.
Many species of Cladophora and Characium are epizoic algae.
Some green algae like Trebouxia, Chlorella form symbiotic association ship with animals like Zoo chlorella and Hydra.
Some green algae form symbiotic association with fungi to form lichens.
Cephaleuros is parasitic algae on leaves of tea, coffee, piper and magnolia plants. Cephaleuros causes red rust of tea.
Chlamydomonas nivalis causes red snow and Chlamydomanas yellowstonensis causes green snow. Some Chlamydomonas species are thermophilic.
The range of thallus structure of Chlorophyceae is as follows:
(i) Unicellular motile forms—e.g., Chlamydomonas.
(ii) Unicellular non-motile forms—e.g., Chlorella.
(iii) Colonial motile form—e.g., Volvox, Eudorina, Pandorina.
(iv) Colonial coccoid forms—e.g., Hydrodictyon, Pediastrum.
(v) Palmelloid forms—e.g., Tetraspora.
(vi) Dendroid forms—e.g., Prasinocladus.
(vii) Un-branched filaments—e.g., Ulothrix, Oedogonium.
(viii) Branched filaments—e.g., Cladophora.
(ix) Heterotrichous forms—e.g., Coleochaete.
(x) Siphonaceous forms—e.g., Vaucheria.
(xi) Parenchymatous forms—e.g., Ulva, Codium, Enteromorpha.
Important Features:
(i) The cells are eukaryotic and contain mitochondria, Golgi bodies, plastids, endoplasmic reticulum and ribosomes.
(ii) The cell wall is made of two layers, the inner layer mainly consisting of cellulose and the outer layer consisting of pectic substances.
(iii) The chloroplasts are well organized, the main pigments are chlorophyll a and b, the other pigments are α and β carotene and xanthophyll’s.
(iv) The shape of the chloroplast is variable. It may be cup shaped e.g., Chlamydomonas, girdle shaped e.g., Ulothrix, reticulate e.g., Cladophora, stellate e.g., Zygonema, spiral e.g., Spirogyra, discoid e.g., Chara or parietal e.g., Draparnaldiopsis.
(v) The reserve food is in form of starch and its formation is associated with pyrenoids.
(vi) The motile reproductive structures i.e., zoospores and gametes have 2, 4 or °c flagella which can be apical, sub apical, equal in size and acronematic type.
(vii) The sexual reproduction can be isogamous, anisogamous or oogamous.
Classification:
Fritsch (1915) divided class Chlorophyceae into nine orders on the basis of morphology and reproductive structures:
Class. Chlorophyceae
Orders:
1. Volvocales
2. Chlorococcales
3. Ulotrichales
4. Cladophorales
5. Chaetophorales
6. Oedogoniales
7. Conjugales
8. Siphonales
9. Charales.
Smith (1955) divided division Chlorophyta into two classes—Chlorophyceae and Charophyceae.
The Chlorophyceae was divided in ten orders and Charophyceae has only single order:
Division. Chlorophyta
I. Class. Chlorophyceae
Orders:
I. Volvocales
2. Tetrasporales
3. Ulotrichales
4. Oedogoniales
5. Ulvales
6. Schizogoniales
7. Chlorococcales
8. Siphonales
9. Siphonocladales
10. Zygnematales.
II. Class. Charophyceae
Order. Charales.
Order: Volvocales
(i) The order Volvocales includes about 60 genera and 500 species.
(ii) The algae of this order are mainly fresh water forms.
(iii) The thallus may be unicellular e.g., Chlamydomonas or motile colony e.g., Volvox, Eudorina and Pandorina.
(iv) The members are characterized by presence of flagellated motile vegetative cells. The flagella can be two or four, equal, apical and acronematic. The cells have large cup shaped chloroplast with single pyrenoid covered with starch plate.
(v) The asexual reproduction takes place by bi-flagellated zoospores, aplanospores or by palmella stage.
(vi) The sexual reproduction can be isogamous, anisogamous and oogamous.
Family: Chlamydomonadaceae:
(i) Algae of this family are mostly unicellular.
(ii) The members are motile. Flagella are generally two or four.
(iii) The asexual reproduction takes place by zoospores or palmella stage,
(iv) The sexual reproduction can be isogamous, anisogamous or oogamous.
(v) The sexual reproduction can be isogamous, anisogamous or oogamous.