Chlorophyceae
| Chlorophyceae | |
|---|---|
| |
Scientific classification 
| |
| (unranked): | Viridiplantae |
| Division: | Chlorophyta |
| Subphylum: | Chlorophytina |
| Class: | Chlorophyceae Wille in Warming, 1884[1] |
| Orders | |
The Chlorophyceae are one of the classes of
General characteristics
- the body may be unicellular, colonial, filamentous or multicellular.
- They are usually green due to the presence of chlorophyll a, chlorophyll b and beta-carotene.
- The chloroplast may be discoid, cup-shaped (e.g. Chlamydomonas), spiral or ribbon shaped[example needed]
- Most chlorophytes have one or more storage bodies called pyrenoids (central proteinaceous body covered with a starch sheath) that are localised around the chloroplast.
- The inner cell wall layer is made of cellulose and the outer layer of pectose.
- Asexual reproduction is by zoospores. They are flagellates produced from the parent cells by mitosis. Also by aplanospores, hypnospores, akinetes, Palmella stage, etc.
- Sexual reproduction of Chlorophyceae is isogamous, anisogamous or oogamous.
- The chlorophycean CW 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.[3]
Reproduction
Vegetative reproduction usually takes place by fragmentation. Asexual reproduction is by flagellated
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.[4]
The sole method of reproduction in Chlorella is asexual and azoosporic. The content of the cell divides into 2,4 (B), 8(C) sometimes daughter protoplasts. Each daughter protoplast rounds off to form a non-motile spore. These autospores (spores having the same distinctive shape as the parent cell) are liberated by the rupture of the parent cell wall (D). On release each autospore grows to become a new individual. The presence of sulphur in the culture medium is considered essential for cell division. It takes place even in the dark with sulphur alone as the source material but under light conditions nitrogen also required in addition. Pearsal and Loose (1937)[citation needed] reported the occurrence of motile cells in Chlorella. Bendix (1964)[citation needed] also observed that Chlorella produces motile cells which might be gametes. These observations have an important bearing on the concept of the life cycle of Chlorella, which at present is considered to be strictly asexual in character.
Asexual reproduction in Chlorella ellipsoides has been studied in detail and the following four phases have been observed during the asexual reproduction.
(i) Growth Phase - During this phase the cells grow in size by utilizing the photosynthetic products.
(ii) Ripening phase - In this phase the cells mature and prepare themselves for division.
(iii) Post ripening phase - During this phase, each mature cell divides twice either in dark or in light. The cells formed in dark are known as dark to light phase, cells again grow in size.
(iv) Division Phase - During this phase the parent cell wall ruptures and unicells are released.
Orders
As of May 2023[update], AlgaeBase accepted the following orders in the class Chlorophyceae:
- Chaetopeltidales C.J.O'Kelly, Shin Watanabe, & G.L.Floyd – 16 species
- Chaetophorales Wille – 225 species
- Chlamydomonadales F.E.Fritsch (also known as Volvocales) – 1793 species
- OedogonialesHeering – 792 species
- Sphaeropleales Luerssen – 941 species
Along with these genera, AlgaeBase recognizes several taxa that are incertae sedis (i.e. unplaced to an order):
- Dangeardinellaceae Ettl - 1 species
Other orders that have been recognized include:
- Dunaliellales – Dunaliella and Dunaliellaceae are placed in Chlamydomonadales by AlgaeBase[5]
- Chlorococcales – Chlorococcum and Chlorococcaceae are placed in Chlamydomonadales by AlgaeBase[6]
- Microsporales – Microspora and Microsporaceae are placed in Sphaeropleales by AlgaeBase[7]
- Tetrasporales – Tetraspora and Tetrasporaceae are placed in Chlamydomonadales by AlgaeBase[8]
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.
See also
References
- ^ 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].
- S2CID 21278460 – via PubMed.)
{{cite journal}}: CS1 maint: multiple names: authors list (link - PMID 21652308– via onlinelibrary.wiley.com.
- ^ Raven, Evert and Eichhorn. The Biology of Plants 7th edition, pg. 335. W. H. Freeman and Company, New York, 2005.
- ^ Guiry, M.D.; Guiry, G.M. "Dunaliella". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.
- ^ Guiry, M.D.; Guiry, G.M. "Chlorococcum". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.
- ^ Guiry, M.D.; Guiry, G.M. "Microspora". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.
- ^ Guiry, M.D.; Guiry, G.M. "Tetraspora". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.