Chlorophyceae
Encyclopedia
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 Pyrenoid
s 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.
Reproduction
Vegetative reproduction usually takes place by fragmentation or by formation of spores. Asexual reproduction is by flagelated zoosporangia.
The sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous, anisogamous or oogamous.
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.
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)
Ulvophyceae by Hoek, Mann and Jahns (1995)
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, 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
Sphaeropleales
In taxonomy, the Sphaeropleales are an order of green algae that used to be called Chlorococcales. This order includes vegetatively non-motile unicellular or colonial taxa that have biflagellate zoospores with flagella that are directly opposed in direction : Sphaeroplea, Atractomorpha,...
. They are usually green due to the dominance of pigments chlorophyll a
Chlorophyll a
Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary...
and chlorophyll b
Chlorophyll b
Chlorophyll b is a form of chlorophyll. Chlorophyll b helps in photosynthesis by absorbing light energy. It is more soluble than chlorophyll a in polar solvents because of its carbonyl group. Its color is yellow, and it primarily absorbs blue light....
.The chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
may be discoid, plate-like, reticulate, cup-shaped, spiral
Spiral
In mathematics, a spiral is a curve which emanates from a central point, getting progressively farther away as it revolves around the point.-Spiral or helix:...
or ribbon shaped in different species. Most of the members have one or more storage bodies called Pyrenoid
Pyrenoid
In cell biology, pyrenoids are organelles, centers of carbon dioxide fixation within the chloroplasts of algae and hornworts. Pyrenoids are not membrane-bound, but specialized areas of the plastid that contain high levels of ribulose-1,5-bisphosphate carboxylase/oxygenase .RubisCO fixes carbon...
s located in the chloroplast.Pyrenoids contain protein besides starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
.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
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
and outer layer of pectose.
Reproduction
Vegetative reproduction usually takes place by fragmentation or by formation of spores. Asexual reproduction is by flagelated zoosporangia.
The sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous, anisogamous or oogamous.
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.
The following orders are typically recognised:
- Dunaliellales (e.g. DunaliellaDunaliellaDunaliella is a genus of algae, specifically of the Dunaliellaceae.Dunaliella sp. are motile, unicellular, rod to ovoid shaped green algae , which are common in marine waters....
) - VolvocalesVolvocalesIn taxonomy, the Volvocales, also known as Chlamydomonadales, are an order of flagellate or pseudociliate green algae, specifically of the Chlorophyceae...
(e.g. VolvoxVolvoxVolvox is a genus of chlorophytes, a type of green algae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox developed its colonial lifestyle .-Description:Volvox is the most developed...
, ChlamydomonasChlamydomonasChlamydomonas is a genus of green algae. They are unicellular flagellates. Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics...
) - ChlorococcalesChlorococcalesChlorococcales is an order of green algae in the class Chlorophyceae. Individual specimens are sometimes found in soil, but mostly in fresh and marine waters...
(e.g. NannochlorisNannochlorisNannochloris is a genus of algae, in the family Coccomyxaceae.-Scientific databases:* * *...
) - OedogonialesOedogonialesThe Oedogoniales are an order of filamentous freshwater green algae of the class Chlorophyceae. The order is well-defined and has several unique features, including asexual reproduction with zoospores that possess stephanokont flagella: numerous short flagella arranged in a subapical whorl...
(e.g. OedogoniumOedogoniumOedogonium is a genus of filamentous green algae. Filamentous means the colony is one cell thick. Reproduces in two ways – sexually and asexually. Reproduces sexually through syngamy. The anthridia which produces sperm and the oogonium which produces the egg, release the sperm and egg. The egg and...
) - SphaeroplealesSphaeroplealesIn taxonomy, the Sphaeropleales are an order of green algae that used to be called Chlorococcales. This order includes vegetatively non-motile unicellular or colonial taxa that have biflagellate zoospores with flagella that are directly opposed in direction : Sphaeroplea, Atractomorpha,...
- ChaetophoralesChaetophoralesIn taxonomy, the Chaetophorales are an order of green algae, specifically the Chlorophyceae....
- Microsporales
- TetrasporalesTetrasporalesIn taxonomy, the Tetrasporales are an order of green algae, specifically the Chlorophyceae....
(e.g. TetrasporaTetrasporaIn taxonomy, Tetraspora is a genus of algae, specifically of the Tetrasporaceae.-Scientific databases:* * *...
)
In older classifications, the term Chlorophyceae is sometimes used to apply to all the green algae except the Charales
Charales
Charales is an order of pondweeds, freshwater algae in the division Charophyta. They are green plants believed to be the closest relatives of the green land plants. Linnaeus established the genus Chara in 1753.-Description:...
, and the internal division is considerably different.
The Orders of the Chlorophyceae as listed by: in Hoek, Mann and Jahns (1995)
- Volvocales
- Chlorococcales
- Chaetophoroales
- Oedogoniales
Ulvophyceae by Hoek, Mann and Jahns (1995)
- Codiolales
- Ulvales