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The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. 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 green algae may store food in the form of oil droplets. They usually have a cell wall made up of an inner layer of cellulose and outer layer of pectose.
Chlorophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it is a highly paraphyletic group of all the green algae within the green plants (Viridiplantae) and thus includes about 7,000 species of mostly aquatic photosynthetic eukaryotic organisms. In newer classifications, it is the sister clade of the streptophytes/charophytes. The clade Streptophyta consists of the Charophyta in which the Embryophyta emerged. In this latter sense the Chlorophyta includes only about 4,300 species. About 90% of all known species live in freshwater. Like the land plants, green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids.
The green algae are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as a sister of the Zygnematophyceae. Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them. The completed clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, multicellular seaweeds. There are about 22,000 species of green algae. Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.
Sphaeropleales is an order of green algae that used to be called Chlorococcales. The order includes some of the most common freshwater planktonic algae such as Scenedesmus and Pediastrum. The Sphaeropleales includes vegetatively non-motile unicellular, colonial, or filamentous taxa. They have biflagellate zoospores with flagella that are directly opposed in direction : Sphaeroplea, Atractomorpha, Neochloris, Hydrodictyon, and Pediastrum. All of these taxa have basal body core connections. Motile cells generally lack cell walls or have only a very fine layer surrounding the cell membrane. Other common characteristics include a robust vegetative cell wall, cup-shaped chloroplasts with large pyrenoids, and relatively large nuclei.
Zoochlorella is a coloquial term for any green algae that lives symbiotically within the body of an aquatic invertebrate animal or a protozoan.
Chlorococcales is a formerly recognized order of green algae in the class Chlorophyceae. As of February 2022, the type family Chlorococcaceae was placed in the order Chlamydomonadales.
The Trebouxiophyceae are a class of green algae, in the division Chlorophyta. Their circumscription within the green algae is not well established due to the need for more genetic studies at higher levels within the group.
Prasiolales is an order of green algae in the class Trebouxiophyceae.
Selenastraceae is a family of green algae in the order Sphaeropleales. Members of this family are common components of the phytoplankton in freshwater habitats worldwide. A few species have been found in brackish and marine habitats, such as in the Baltic Sea.
Dictyochloris is a genus of green algae in the class Chlorophyceae. It is the sole genus of the family Dictyochloridaceae. It is commonly found in terrestrial and subaerial habitats.
Dictyosphaerium is a genus of green algae, in the family Chlorellaceae. It occurs in freshwater habitats around the world and is planktonic.
Golenkinia is a genus of green algae first described in 1894 by Robert Chodat. The genus is named for the Russian phycologist Mikhail Iljitsch Golenkin. Golenkinia species live in fresh water and are found around the world.
Lagerheimia is a genus of green algae in the family Oocystaceae. It is commonly found in freshwater habitats all over the world, although some species are rare and have only been recorded from Europe or the United States.
Pleurastrum is a genus of green algae, specifically of the Chlorophyceae. As of February 2022, it was the only genus in the family Pleurastraceae.
Radiofilum is a genus of green algae in the class Chlorophyceae. It is a freshwater genus; they are often found in soft, boggy or acidic waters.
Selenastrum is a genus of green algae in the family Selenastraceae. It is common in freshwater habitats around the world. Most species prefer temperate or warm-temperate waters.
Tetrastrum is a genus of green algae (Chlorophyta). It is a common component of the phytoplankton of freshwater habitats, particularly eutrophic and alkaline waters.
Characiaceae is a family of green algae in the order Sphaeropleales. It contains epiphytic or planktonic algae that are unicellular or colonial. The cells are heteropolar, with basal and apical ends having different shapes. The daughter cells are often retained in the cell wall of the old mother cell, whose cell wall becomes gelatinized.
The Klebsormidiaceae are a family containing five genera of charophyte green alga forming multicellular, non-branching filaments. The genus Chlorokybus was previously included as well, but this problematic and poorly known genus is now placed in a separate class Chlorokybophyceae.
References
- ↑ Guiry, M.D. & Guiry, G.M. (2007). "Class: Pleurastrophyceae taxonomy browser". AlgaeBase version 4.2 World-wide electronic publication, National University of Ireland, Galway. Retrieved 2007-09-23.
- ↑ Lewis, L. A & R. M. McCourt (2004). "Green algae and the origin of land plants". American Journal of Botany . 91 (10): 1535–1556. doi:10.3732/ajb.91.10.1535. PMID 21652308.
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