Chlorophyta: Green Algae Characteristics

CHLOROPHYTA (Green Algae) Characteristics

• Covered by a cell wall composed of cellulose and pectin.
• Contain pigments such as chlorophyll a, chlorophyll b, β-carotene, and xanthophylls.
• Store food reserves in the form of starch.
• Reproduce both sexually (isogamy, anisogamy, oogamy) and asexually (via akinetes, aplanospores, and zoospores).
• Found in various habitats, including aquatic (both fresh and marine) and terrestrial environments.

Economic Importance

• Serve as food sources for humans and livestock.
• Contribute significantly to oxygen production.
• Used in sewage treatment processes.
• Contain crude oil reserves in the seabed.
• Genus Chlorella is a notable protein, fat, and carbohydrate source.

Classification

Class Chlorophyceae

• Includes unicellular and multicellular organisms.
• Lacks transverse whorls of branches along a central filamentous axis.
• Comprises approximately 425 genera and 6,500 species.

Order Volvocales

• Features motile, flagellated vegetative cells.
• Sexual reproduction varies between unicellular (division) and colonial (colony division).
• Asexual reproduction involves isogamy, anisogamy, and oogamy.
• Families include Chlamydomonadaceae (e.g., Chlamydomonas) and Volvocales (e.g., Volvox).

Order Ulotrichales

• Consists of cells united in simple or branched filaments.
• Thallus differentiated into prostate and erect portions.
• Sexual and asexual reproduction via zoospores (biflagellate or quadriflagellate).
• Families include Ulothrix and Protococcaceae (e.g., Protococcus).

Order Cladophorales

• Features multinucleate or coenocytic cells with reticulated chloroplast.
• Asexual reproduction through quadriflagellate zoospores and akinetes.
• Includes families such as Cladophoraceae (e.g., Cladophora) and Pithophora.

Order Oedogoniales

• Characterized by cylindrical, uninucleate cells with reticulate chloroplasts.
• Asexual reproduction produces zoospores; sexual reproduction is oogamous.
• Family Oedogoniaceae includes the genus Oedogonium.

Order Zygnematales (Conjugales)

• Gametes are amoeboid and non-flagellated.
• Cells can be solitary or form unbranched filaments.
• Sexual reproduction occurs through isogamy.
• Includes families like Zygnemataceae (e.g., Spirogyra, Zygnema) and Desmidiaceae (e.g., Cosmarium, Closterium).

Order Chlorococcales

• Lacks vegetative cells; aplanospores are produced as non-flagellated spores.
• Reproduces sexually through isogamy, anisogamy, or oogamy.
• Families encompass Chroococcaceae (e.g., Chlorococcum), Oocystaceae (e.g., Chlorella), and Scenedesmaceae (e.g., Scenedesmus).

Macroalgae Orders

Order Siphonocladales

• Thalli are anchored by rhizoids.
• Asexual reproduction through quadriflagellate zoospores; sexual reproduction may be isogamous or oogamous.
• Family Valoniaceae includes the genus Valonia.

Order Dasycladales

• Thalli possess an erect central axis with branch whorls.
• Contains a single diploid nucleus.
• Family Dasycladaceae includes genera Acetabularia and Halicoryne.

Order Ulvales

• Thalli can be sheets, tubes, or solid cylinders.
• Asexual reproduction through quadriflagellate zoospores; sexual reproduction can occur by isogamy or heterogamy.
• Includes families like Ulvaceae (e.g., Ulva, Enteromorpha).

Order Siphonales

• Characterized by a single branched multinucleate thallus.
• Sexual reproduction includes isogamy, anisogamy, and oogamy.
• Family Caulerpaceae includes the genus Caulerpa and other related genera.

Class Charophyceae

• Known as stoneworts with erect branched thalli formed of regular nodes and internodes.
• Sexual reproduction is oogamous, involving one-celled oogonia.
• Genus Chara is recognized for its watery “meadows” and high chlorophyll content, giving it a vibrant green color.