Chlorophyceae

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Chlorophyceae
Pediastrum.jpg
Scientific classification edit
(unranked): Viridiplantae
Division: Chlorophyta
Class: Chlorophyceae
Wille in Warming, 1884[1]
Orders[2]

The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example, the chlorophycean CW clade, and chlorophycean DO clade, are defined by the arrangement of their flagella. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g. Chlamydomonadales. Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g. Sphaeropleales. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some algae may store food in the form of oil droplets. Green algae usually have a rigid cell wall made up of an inner layer of cellulose and outer layer of pectose.

General characteristics[edit]

  • Plant body may be unicellular, colonial or filamentous, or multicellular
  • They are usually green due to the dominance of chlorophyll A and B and beta carotene.
  • The pigments present in green algae are chlorophyll a, chlorophyll b, beta- carotine.
  • The chloroplast may be discoid, cup-shaped(chlamydomonas), spiral or ribbon shaped(spyrogyra) in different species.
  • Most of the members have one or more storage bodies called pyrenoids(central protentious body covered with starch sheath) that are localised around the chloroplast.
  • Cell wall is made of cellulose {inner side} and the outer layer is from pectose.
  • Asexual reproduction is by zoospores. They are flagellates produced from the parent cells by mitosis.Also by aplanospores, hepnospores, akinetes, palmella stage etc.
  • Sexual reproduction of plants is by isogamus, anisogamus or oogamus
  • Starch is deposited on small bodies called pyrenoids

Reproduction[edit]

Vegetative reproduction usually takes place by fragmentation. Asexual reproduction is by flagellated zoospores. And haplospore, perrination (akinate and palmellastage). Asexual reproduction by mytospore absent in spyrogyra. Sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous e.g. Chlamydomonas, Spirogyara. anisogamous e.g. Chlamydomonas, Ulothrix or Ooulothrix e.g. Chlamydomonas, Volvox, Chara. Chlamydomonas has all three types of sexual reproduction.

They share many similarities with the higher plants, including the presence of asymmetrical flagellated cells, the breakdown of the nuclear envelope at mitosis, and the presence of phytochromes, flavonoids, and the chemical precursors to the cuticle.[3]

Classification[edit]

The following orders are typically recognised:

In older classifications, the term Chlorophyceae is sometimes used to apply to all the green algae except the Charales, and the internal division is considerably different.

The Orders of the Chlorophyceae as listed by: in Hoek, Mann and Jahns (1995)[4]

  • Volvocales
  • Chlorococcales
  • Chaetophoroales
  • Oedogoniales

See also[edit]

References[edit]

  1. ^ Warming, E., 1884. Haandbog i den systematiske botanik. Anden gjennemsete udgave. 2nd ed. Kjøbenhavn, 434 pp. German translation (1890) of the 2nd Danish edition available at archive.org: [1]. English translation (1895) of the 3rd Danish edition (1892) available at archive.org: [2].
  2. ^ Guiry, M.D.; Guiry, G.M. (2007). "Class: Chlorophyceae taxonomy browser". AlgaeBase version 4.2 World-wide electronic publication, National University of Ireland, Galway. Retrieved 2007-09-23.
  3. ^ Raven, Evert and Eichhorn. The Biology of Plants 7th edition, pg. 335. W. H. Freeman and Company, New York, 2005.
  4. ^ Hoek, C.van den, Mann, D.G. and Jahns, H.M. 1995. Algae An Introduction to Phycology. Cambridge University Press, Cambridge

External links[edit]