Editing Chlorophyceae

{{Short description|Class of green algae}}
{{Automatic taxobox
| image = Pediastrum.jpg
| image_caption = Light micrograph of ''[[Pediastrum]]'' sp.
| taxon = Chlorophyceae
| authority = Wille ''in'' [[Eugenius Warming|Warming]], 1884<ref>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: [https://archive.org/details/handbuchdersyst00knobgoog]. English translation (1895) of the 3rd Danish edition (1892) available at archive.org: [https://archive.org/details/handbookofsystem00warm].</ref>
| subdivision_ranks = Orders
| subdivision = [[#Orders|See text]].
}}

The '''Chlorophyceae''', also known as '''chlorophycean algae''', are one of the classes of [[green alga]]e, within the phylum [[Chlorophyta]]. They are a large assemblage of mostly freshwater and terrestrial organisms; many members are important primary producers in the ecosystems they inhabit. Their body plans are diverse and range from single flagellated or non-flagellated cells to colonies or filaments of cells.<ref name=Graham>{{Cite book|last1=Graham|first1=J.E.|last2=Wilcox|first2=L.W.|last3=Graham|first3=L.E.|title=Algae, 2nd Edition|publisher=Pearson|year=2009|isbn=9780321603128|pages=616}}</ref> The class Chlorophyceae has been distinguished on the basis of ultrastructural morphology;<ref>{{Cite journal|last=Štenclová, Lenka, Karolina Fučíková, Jan Kaštovský, and Marie Pažoutová|date=December 2017|title=Molecular and morphological delimitation and generic classification of the family Oocystaceae (Trebouxiophyceae, Chlorophyta)|url=https://pubmed.ncbi.nlm.nih.gov/28833138/|journal=Journal of Phycology|volume=53| issue = 6|pages=1263–1282| doi=10.1111/jpy.12581 | pmid=28833138 |bibcode=2017JPcgy..53.1263S | s2cid=21278460 |via=PubMed}}</ref> molecular traits are also being used to classify taxa within the class.<ref name=Graham/>

==Description==
Chlorophycean algae are [[eukaryotic]] organisms composed of [[cell (biology)|cell]]s which occur in a variety of forms. Depending on the species, Chlorophyceae can grow unicellular (e.g. ''[[Chlamydomonas]])'', colonial (e.g. ''[[Volvox]]''), coenocytic (e.g. ''[[Characiosiphon]]''), or filamentous (e.g. ''[[Chaetophora (alga)|Chaetophora]]''). In their vegetative state, some members have [[flagella]] while others produce them only in reproductive stages; still others never produce flagella.<ref name=Graham/>

===Chloroplasts===
Chlorophycean algae have [[chloroplast]]s and nearly all members are [[photosynthetic]]. There are a few exceptions, such as ''[[Polytoma]]'', which have plastids that have lost the ability to photosynthesize.<ref>{{cite journal|doi= 10.1186/s12915-022-01263-w|doi-access= free|title= A new lineage of non-photosynthetic green algae with extreme organellar genomes|date= 2022|last1= Pánek|first1= Tomáš|last2= Barcytė|first2= Dovilė|last3= Treitli|first3= Sebastian C.|last4= Záhonová|first4= Kristína|last5= Sokol|first5= Martin|last6= Ševčíková|first6= Tereza|last7= Zadrobílková|first7= Eliška|last8= Jaške|first8= Karin|last9= Yubuki|first9= Naoji|last10= Čepička|first10= Ivan|last11= Eliáš|first11= Marek|journal= BMC Biology|volume= 20|issue= 1|page= 66|pmid= 35296310|pmc= 8928634}}</ref> They are usually green due to the presence of [[chlorophyll]] [[chlorophyll a|''a'']] and [[chlorophyll b|''b'']]; they can also contain the pigment [[Β-Carotene|beta-carotene]]. Chloroplasts are diverse in morphology and include many forms, including, cup-shaped (e.g. ''Chlamydomonas''), or axial, or parietal and reticulate (e.g. ''[[Oedogonium]]'').<ref name=Graham/>

In many species, there may be one or more storage bodies called [[pyrenoid]]s (central proteinaceous body covered with a starch sheath) that are localised around the chloroplast.<ref>{{cite journal|doi=10.1007/s00239-002-2338-9 |title=Differences in pyrenoid morphology are correlated with differences in the rbcL genes of members of the ''Chloromonas'' lineage (Volvocales, Chlorophyceae) |date=2002 |last1=Nozaki |first1=Hisayoshi |last2=Onishi |first2=Keisuke |last3=Morita |first3=Eiko |journal=Journal of Molecular Evolution |volume=55 |issue=4 |pages=414–430 |pmid=12355262 |bibcode=2002JMolE..55..414N }}</ref> Some algae may also store food in the form of oil droplets.<ref name=":1">{{cite journal| vauthors = Melkonian M, Preisig HR |date=1984 |title= An ultrastructural comparison between Spermatozopsis and Dunaliella (Chlorophyceae)  |journal=Plant Systematics and Evolution | volume=146|issue=1–2|pages=31–46|doi=10.1007/BF00984052 |bibcode=1984PSyEv.146...31M }}</ref> The inner cell wall layer is made of cellulose and the outer layer of pectose.

===Ultrastructure===
Cells of Chlorophyceae usually have two or four [[flagella]], but in some cases may have numerous flagella. The flagella emerge from the apex of the cell, and are connected to the nucleus via [[rhizoplast]]s.<ref name=Graham/> The arrangement of flagella may be in one of two configurations, termed CW ("clockwise") or DO ("directly opposed"). In the CW configuration, the [[basal bodies]] are arranged clockwise in the 1–7 o'clock position. In the DO configuration, the basal bodies are arranged in 12–6 o'clock. Taxa with the CW arrangement and DO arrangement correspond to two different [[clade]]s, roughly corresponding to the orders [[Chlamydomonadales]] and [[Sphaeropleales]], respectively.<ref>{{Cite journal|last=Lewis, Louise A. and Richard M. McCourt|date=2004-10-01|title=Green algae and the origin of land plants|url=https://bsapubs.onlinelibrary.wiley.com/doi/10.3732/ajb.91.10.1535|journal=American Journal of Botany|volume=91| issue = 10|pages=1535–1556| doi=10.3732/ajb.91.10.1535 | pmid=21652308 |bibcode=2004AmJB...91.1535L |via=onlinelibrary.wiley.com}}</ref>

A combination of [[ultrastructural]] features are characteristic of the Chlorophyceae. These include: closed [[mitosis]], the [[telophase]] spindle collapsing before [[cytokinesis]], and a system of [[microtubule]]s called a phycoplast running parallel to the plane of cytokinesis.<ref name=Graham/>

{{Gallery|title=Diversity of Chlorophyceae|align=center|
|File:Chlamydomonas globosa - 400x (13263097835).jpg
 |''Chlamydomonas globosa'' 400x
 |alt1=Light micrograph of Chlamydomonas globosa a round green, single cell 
|File:Volvox aureus.jpg
 |''[[Volvox aureus]]''
 |alt2=Light micrograph of Volvox aureus, a spherical colonial green algae with multiple dense inner colonies
|File: Pediastrum duplex phv.jpg
 |''Pediastrum duplex''
 |alt3=Light micrograph of Pediastrum duplex, a star-shaped colonial green alga 
}}

==Reproduction==
Chlorophyceae can reproduce both asexually and sexually. In [[asexual reproduction]], cells may produce [[autospore]]s, [[aplanospore]]s or [[zoospore]]s. Autospores (by definition) lack flagella and appear as smaller versions of vegetative cells. Zoospores typically have an elongate, hydrodynamic shape and often have [[eyespot apparatus|eyespots]]. Aplanospores are similar to zoospores in that they have characteristics typical of zoospores (such as [[contractile vacuole]]s), but lack flagella.<ref name=AlgaeBase>{{AlgaeBase genus|id= 43426 |title=''Chlorella'' Beyerinck [Beijerinck], 1890, nom. cons.|access-date=2025-01-14}}</ref>

In addition to normal asexual reproduction, some genera such as ''Chlamydomonas'' and ''Dunaliella'' can go through a temporary phase known as the "palmella stage", in which flagella are absent and the cells divide vegetatively within a common mucilaginous envelope.<ref>{{cite book|doi= 10.1007/978-94-017-7321-8_1|chapter= General Characteristics of Algae|title= The Algae World|series= Cellular Origin, Life in Extreme Habitats and Astrobiology|date= 2015|last1= Sahoo|first1= Dinabandhu|last2= Baweja|first2= Pooja|volume= 26|pages= 3–29|isbn= 978-94-017-7320-1}}</ref> Algae enter the palmella stage in response to stressful conditions, such as changes in salinity or predation.<ref>{{cite journal|doi=10.3389/fpls.2017.00810|doi-access=free |title=Salinity-Induced Palmella Formation Mechanism in Halotolerant Algae Dunaliella salina Revealed by Quantitative Proteomics and Phosphoproteomics |date=2017 |last1=Wei |first1=Sijia |last2=Bian |first2=Yangyang |last3=Zhao |first3=Qi |last4=Chen |first4=Sixue |last5=Mao |first5=Jiawei |last6=Song |first6=Chunxia |last7=Cheng |first7=Kai |last8=Xiao |first8=Zhen |last9=Zhang |first9=Chuanfang |last10=Ma |first10=Weimin |last11=Zou |first11=Hanfa |last12=Ye |first12=Mingliang |last13=Dai |first13=Shaojun |journal=Frontiers in Plant Science |volume=8 |page=810 |pmid=28588593 |pmc=5441111 }}</ref> Additionally, ''[[Haematococcus]]'' produces resistant stages with thick [[cell wall]]s, termed [[akinete]]s.<ref>{{cite journal|doi=10.4490/algae.2023.38.3.9 |title=The description of ''Haematococcus privus'' sp. nov. (Chlorophyceae, Chlamydomonadales) from North America |date=2023 |last1=Buchheim |first1=Mark A. |last2=Silver |first2=Ashley |last3=Johnson |first3=Haley |last4=Portman |first4=Richard |last5=Toomey |first5=Matthew B. |journal=Algae |volume=38 |pages=1–22 |doi-access=free }}</ref>

[[Sexual reproduction]] shows considerable variation in the type and formation of sex cells; it may be [[isogamous]] (with two morphologically identical gamete types), [[anisogamous]] (with two morphologically distinct gamete types), and [[oogamous]] (with larger, nonmotile eggs and smaller motile sperm cells). Members of Chlorophyceae that undergo sexual reproduction have a zygotic life cycle, in which the [[zygote]]s are the only [[diploid]] stages. Zygotes may have thick and/or spiny cell walls; these are called hypnozygotes and they also function as resting stages.<ref name=Graham/>
 
They share many similarities with 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.<ref>Raven, Evert and Eichhorn. ''The Biology of Plants'' 7th edition, pg. 335. W. H. Freeman and Company, New York, 2005.</ref> However, unlike higher plants they do not go through a multicellular [[alternation of generation]]s.<ref name=Graham/>

==Taxonomy==
The current taxonomy of algae is based on [[molecular phylogenetic]]s. Older classifications are simpler and more morphologically aligned; however, these classifications are recognized as artificial due to the extensive [[morphological convergence]] present within the class (and more broadly within algae).<ref name=Graham/> In even older, historical classifications, the term Chlorophyceae is sometimes used to apply to all the green algae except the [[Charales]], and the internal division is considerably different.{{cn|date=August 2024}}

{{As of|2023|May}}, [[AlgaeBase]] accepted the following orders in the class Chlorophyceae:
*[[Chaetopeltidales]] <small>C.J.O'Kelly, Shin Watanabe, & G.L.Floyd</small> – 16 species
*[[Chaetophorales]] <small>Wille</small> – 225 species
*[[Chlamydomonadales]] <small>F.E.Fritsch</small> (also known as Volvocales) – 1793 species
*[[Oedogoniales]] <small>Heering</small> – 792 species
*[[Sphaeropleales]] <small>Luerssen</small> – 941 species

Along with these genera, AlgaeBase recognizes several taxa that are [[incertae sedis]] (i.e. unplaced to an order):
*[[Dangeardinellaceae]] <small>Ettl</small> - 1 species

Other orders that have been recognized include:
* Dunaliellales – ''[[Dunaliella]]'' and [[Dunaliellaceae]] are placed in Chlamydomonadales by AlgaeBase<ref name=AB_t6930>{{AlgaeBase taxon|name=''Dunaliella''|id=6930|access-date=2022-02-25}}</ref>
* Chlorococcales – ''[[Chlorococcum]]'' and [[Chlorococcaceae]] are placed in Chlamydomonadales by AlgaeBase<ref name=AB_t8026>{{AlgaeBase taxon|name=''Chlorococcum''|id=8026|access-date=2022-02-25}}</ref>
* Microsporales – ''[[Microspora]]'' and [[Microsporaceae]] are placed in Sphaeropleales by AlgaeBase<ref name=AB_t8018>{{AlgaeBase taxon|name=''Microspora''|id=8018|access-date=2022-02-25}}</ref>
* Tetrasporales – ''[[Tetraspora]]'' and [[Tetrasporaceae]] are placed in Chlamydomonadales by AlgaeBase<ref name=AB_t6908>{{AlgaeBase taxon|name=''Tetraspora''|id=6908|access-date=2022-02-25}}</ref>

===Phylogeny===
Current thinking of phylogenetic relationships are as follows:<ref>{{cite journal|doi=10.7717/peerj.6899|doi-access=free |title=Order, please! Uncertainty in the ordinal-level classification of Chlorophyceae |date=2019 |last1=Fučíková |first1=Karolina |last2=Lewis |first2=Paul O. |last3=Neupane |first3=Suman |last4=Karol |first4=Kenneth G. |last5=Lewis |first5=Louise A. |journal=PeerJ |volume=7 |pages=e6899 |pmid=31143537 |pmc=6525593 }}</ref>

{{clade
|1=
{{clade
|1=
{{clade
|1={{clade
|1=Sphaeropleales ''[[sensu lato]]''
|2=Chlamydomonadales (= Volvocales) ''sensu lato''
}}
|label2=OCC clade
|2={{clade
|1=Oedogoniales
|2={{clade
|1=Chaetopeltidales
|2=Chaetophorales
}}
}}
}}
|2=Trebouxiophyceae (outgroup)
}}
}}

==See also==
* [[List of Chlorophyceae genera]]

==References==
{{Reflist}}

==External links==
* [http://www.algaebase.org/browse/taxonomy/?id=4355&-session=abv4:4E5E144B1b45e25996Ihq2483A24 AlgaeBase]

{{Plant classification}}
{{Taxonbar|from=Q132609}}
{{Authority control}}

[[Category:Chlorophyceae| ]]
[[Category:Chlorophyta classes| ]]
[[Category:Green algae classes]]