green algae

Green algae have chloroplasts that contain chlorophyll a and b, giving them a bright green colour, as well as the accessory pigments beta carotene (red-orange) and xanthophylls (yellow) in stacked thylakoids.Burrows 1991. Seaweeds of the British Isles. Volume 2 Natural History Museum, London. {{ISBN|0-565-00981-8}}{{cite book | vauthors = van den Hoek C, Mann DG, Jahns HM | year = 1995 | url = https://books.google.com/books?id=xuUoiFesSHMC | title = Algae An introduction to phycology | publisher = Cambridge University Press | location = Cambridge | isbn = 978-0-521-30419-1 }} The cell walls of green algae usually contain cellulose, and they store carbohydrate in the form of starch.{{cite book |vauthors=Judd WS, Campbell CS, Kellogg EA, Stevens PF, Donoghue MJ | publisher = Sinauer Associates Inc. | location = Sunderland Mass. | date = 2002 | title = Plant systematics, a phylogenetic approach. | isbn = 978-0-87893-403-4 | pages = [https://archive.org/details/plantsystematics0002unse/page/156 156] | url = https://archive.org/details/plantsystematics0002unse/page/156 }}

All green algae have mitochondria with flat cristae. When present, paired flagella are used to move the cell. They are anchored by a cross-shaped system of microtubules and fibrous strands. Flagella are only present in the motile male gametes of charophytes{{Cite journal |doi = 10.1016/0041-008x(92)90204-6|pmid = 1539170|title = Letter to the editor|journal = Toxicology and Applied Pharmacology|volume = 112|issue = 2|pages = 331–332|year = 1992| vauthors = Roberts DW }} bryophytes, pteridophytes, cycads and Ginkgo, but are absent from the gametes of Pinophyta and flowering plants.

Members of the class Chlorophyceae undergo closed mitosis in the most common form of cell division among the green algae, which occurs via a phycoplast.{{cite journal |vauthors=Pickett-Heaps J | year = 1976 | title = Cell division in eucaryotic algae | journal = BioScience | volume = 26 | issue = 7| pages = 445–450 | doi=10.2307/1297481| jstor = 1297481 }} By contrast, charophyte green algae and land plants (embryophytes) undergo open mitosis without centrioles. Instead, a 'raft' of microtubules, the phragmoplast, is formed from the mitotic spindle and cell division involves the use of this phragmoplast in the production of a cell plate.P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): Biology of Plants, 7th Edition, W.H. Freeman and Company Publishers, New York, {{ISBN|0-7167-1007-2}}

Photosynthetic eukaryotes originated following a primary endosymbiotic event, where a heterotrophic eukaryotic cell engulfed a photosynthetic cyanobacterium-like prokaryote that became stably integrated and eventually evolved into a membrane-bound organelle: the plastid.{{cite journal | vauthors = Keeling PJ | title = The endosymbiotic origin, diversification and fate of plastids | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 365 | issue = 1541 | pages = 729–48 | date = March 2010 | pmid = 20124341 | pmc = 2817223 | doi = 10.1098/rstb.2009.0103 }} This primary endosymbiosis event gave rise to three autotrophic clades with primary plastids: the (green) plants (with chloroplasts) the red algae (with rhodoplasts) and the glaucophytes (with muroplasts).{{cite book | vauthors = De Clerck O, Bogaert KA, Leliaert F |volume=64|year=2012|pages=55–86|issn=0065-2296|doi=10.1016/B978-0-12-391499-6.00002-5|series=Advances in Botanical Research|isbn=9780123914996| title = Genomic Insights into the Biology of Algae | chapter = Diversity and Evolution of Algae |chapter-url=https://books.google.com/books?id=lE6r5q5op94C&pg=PA55 }}

File:Intertidal greenalgae.jpg on rock substratum at the ocean shore; some green seaweeds like Ulva are quick to utilize inorganic nutrients from land runoff, and thus can be indicators of nutrient pollution]]

Green algae are often classified with their embryophyte descendants in the green plant clade Viridiplantae (or Chlorobionta). Viridiplantae, together with red algae and glaucophyte algae, form the supergroup Primoplantae, also known as Archaeplastida or Plantae sensu lato. The ancestral green alga was a unicellular flagellate.

The Viridiplantae diverged into two clades. The Chlorophyta include the early diverging prasinophyte lineages and the core Chlorophyta, which contain the majority of described species of green algae. The Streptophyta include charophytes and land plants. Below is a consensus reconstruction of green algal relationships, mainly based on molecular data.{{cite journal | vauthors = Lewis LA, McCourt RM | title = Green algae and the origin of land plants | journal = American Journal of Botany | volume = 91 | issue = 10 | pages = 1535–56 | date = October 2004 | pmid = 21652308 | doi = 10.3732/ajb.91.10.1535 }}{{cite journal |last1= Leliaert |first1=Frederik |last2=Smith |first2=David R. |last3=Moreau |first3=Hervé |last4=Herron |first4=Matthew D. |last5=Verbruggen |first5=Heroen |last6=Delwiche |first6=Charles F. |last7=De Clerck |first7=Olivier | name-list-style = vanc |title=Phylogeny and Molecular Evolution of the Green Algae | url = https://frederikleliaert.files.wordpress.com/2013/05/2012_leliaert_crps.pdf |s2cid-access=free |journal=Critical Reviews in Plant Sciences |volume=31 |year=2012 |pages=1–46 |doi=10.1080/07352689.2011.615705 |s2cid=17603352 |url-status=live |archive-url= https://web.archive.org/web/20230524164529/https://frederikleliaert.files.wordpress.com/2013/05/2012_leliaert_crps.pdf |archive-date= May 24, 2023 }}{{cite journal | vauthors = Marin B | title = Nested in the Chlorellales or independent class? Phylogeny and classification of the Pedinophyceae (Viridiplantae) revealed by molecular phylogenetic analyses of complete nuclear and plastid-encoded rRNA operons | journal = Protist | volume = 163 | issue = 5 | pages = 778–805 | date = September 2012 | pmid = 22192529 | doi = 10.1016/j.protis.2011.11.004 }}{{cite journal | vauthors = Laurin-Lemay S, Brinkmann H, Philippe H | title = Origin of land plants revisited in the light of sequence contamination and missing data | journal = Current Biology | volume = 22 | issue = 15 | pages = R593–4 | date = August 2012 | pmid = 22877776 | doi = 10.1016/j.cub.2012.06.013 | doi-access = free }}{{cite journal | vauthors = Ruhfel BR, Gitzendanner MA, Soltis PS, Soltis DE, Burleigh JG | title = From algae to angiosperms-inferring the phylogeny of green plants (Viridiplantae) from 360 plastid genomes | journal = BMC Evolutionary Biology | volume = 14 | pages = 23 | date = February 2014 | pmid = 24533922 | pmc = 3933183 | doi = 10.1186/1471-2148-14-23 | doi-access = free }}{{cite journal | vauthors = Leliaert F, Tronholm A, Lemieux C, Turmel M, DePriest MS, Bhattacharya D, Karol KG, Fredericq S, Zechman FW, Lopez-Bautista JM | title = Chloroplast phylogenomic analyses reveal the deepest-branching lineage of the Chlorophyta, Palmophyllophyceae class. nov | journal = Scientific Reports | volume = 6 | pages = 25367 | date = May 2016 | pmid = 27157793 | pmc = 4860620 | doi = 10.1038/srep25367 | bibcode = 2016NatSR...625367L }}{{Cite book|url=https://books.google.com/books?id=S4LxB9MRdzMC&pg=PA158 |title=The Tree of Life: A Phylogenetic Classification|last1=Lecointre|first1= Guillaume |last2=Guyader|first2=Hervé Le | name-list-style = vanc |date=2006|publisher=Harvard University Press|isbn=9780674021839|language=en}}{{cite journal | vauthors = Sánchez-Baracaldo P, Raven JA, Pisani D, Knoll AH | title = Early photosynthetic eukaryotes inhabited low-salinity habitats | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 114 | issue = 37 | pages = E7737–E7745 | date = September 2017 | pmid = 28808007 | doi = 10.1073/pnas.1620089114 | pmc=5603991| bibcode = 2017PNAS..114E7737S | doi-access = free }}{{cite journal |vauthors=Gitzendanner MA, Soltis PS, Wong GK, Ruhfel BR, Soltis DE |date=March 2018 |title=Plastid phylogenomic analysis of green plants: A billion years of evolutionary history |journal=American Journal of Botany |volume=105 |issue=3 |pages=291–301 |doi=10.1002/ajb2.1048 |pmid=29603143 |doi-access=free}}{{cite journal | vauthors = Lemieux C, Otis C, Turmel M | title = Ancestral chloroplast genome in Mesostigma viride reveals an early branch of green plant evolution | language = En | journal = Nature | volume = 403 | issue = 6770 | pages = 649–52 | date = February 2000 | pmid = 10688199 | doi = 10.1038/35001059 | bibcode = 2000Natur.403..649L | doi-access = free }}{{Cite journal|last1=Riediger|first1=Matthias|last2=Hihara|first2=Yukako|last3=Hess |first3=Wolfgang R.|date= 2018-06-01 |title=From cyanobacteria and algae to land plants: The RpaB/Ycf27 regulatory network in transition|journal=Perspectives in Phycology|language=en |volume=5|issue=1|pages=13–25|doi=10.1127/pip/2018/0078|s2cid=90444313|issn=2198-011X}}{{Citation|last1=Turmel|first1=Monique|title=Evolution of the Plastid Genome in Green Algae|date=2018|work=Advances in Botanical Research|pages=157–193|publisher=Elsevier|doi=10.1016/bs.abr.2017.11.010|isbn=9780128134573|last2=Lemieux|first2=Claude}}{{Cite journal |author1=Linzhou Li |author2=Sibo Wang |author3=Hongli Wang |author4=Sunil Kumar Sahu |author5=Birger Marin |author6=Haoyuan Li |author7=Yan Xu |author8=Hongping Liang |author9=Zhen Li |author10=Shifeng Chen |author11=Tanja Reder |date=22 June 2020 |title=The genome of Prasinoderma coloniale unveils the existence of a third phylum within green plants |journal=Nature Ecology & Evolution |volume=4 |issue=9 |pages=1220–1231 |doi=10.1038/s41559-020-1221-7 |pmc=7455551 |pmid=32572216 |doi-access=free |author22=Yves Van de Peer |author23=Michael Melkonian |author24=Huan Liu |author21=Xin Liu |author20=Xun Xu |author19=Gane Ka-Shu Wong |author17=Huanming Yang |author16=Hongli Du |author15=Barbara Melkonian |author14=Morten Petersen |author13=Sebastian Wittek |author12=Zehra Çebi |author18=Jian Wang}}{{Excessive citations inline|date=November 2021}}

{{clade| style=font-size:80%;line-height:80%

|1={{clade

|label1=Prasinodermophyta

|1={{clade

|1=Palmophyllophyceae (prasinophyte clade VI)

|2=Prasinodermophyceae

}}

|2={{clade

|label1=Chlorophyta

|1={{clade

|1={{clade

|1={{clade

|1={{clade

|label1=core Chlorophyta

|1={{clade

|label1=Chlorophytina

|1={{clade

|1={{clade

|1={{clade

|1=Ulvophyceae

|2=Chlorophyceae

}}

|2=Trebouxiophyceae

}}

|2=Chlorodendrophyceae

}}

|2=Pedinophyceae

}}

|2=Prasinophytes Clade VIIA

}}

|2={{clade

|1=Prasinophytes Clade VIIC

|2=Pycnococcaceae

}}

}}

|2=Nephroselmidophyceae

}}

|2={{clade

|1=Mamiellophyceae

|2=Pyramimonadales

}}}}

|label2=Streptophyta/

|sublabel2=Charophyta

|2={{clade

|1={{clade

|1=Mesostigmatophyceae

|2={{clade

|1=Spirotaenia

|2=Chlorokybophyceae

}}

}}

|2={{clade

|1=Streptofilum

|2={{clade

|1=Klebsormidiophyceae

|label2=Phragmoplastophyta

|2={{clade

|1=Charophyceae

|2={{clade

|1=Coleochaetophyceae

|2={{clade

|1={{clade

|1=Zygnematophyceae

|2=Mesotaeniaceae s.s.}}

|2=Embryophyta (land plants)

}}

}}

}}

}}

}}

}}}}}}

|label1=Viridiplantae/|sublabel1=green algae}}

The basal character of the Mesostigmatophyceae, Chlorokybophyceae and spirotaenia are only more conventionally basal Streptophytes.

The algae of this paraphyletic group "Charophyta" were previously included in Chlorophyta, so green algae and Chlorophyta in this definition were synonyms. As the green algae clades get further resolved, the embryophytes, which are a deep charophyte branch, are included in "algae", "green algae" and "Charophytes", or these terms are replaced by cladistic terminology such as Archaeplastida, Plantae/Viridiplantae, and streptophytes, respectively.{{Cite book|title=Handbook of the Protists|last1=Cook|first1=Martha E.|last2=Graham|first2=Linda E. |chapter=Chlorokybophyceae, Klebsormidiophyceae, Coleochaetophyceae | name-list-style = vanc |date=2017|publisher=Springer International Publishing|isbn=9783319281476|editor-last=Archibald|editor-first=John M.|pages=185–204|doi=10.1007/978-3-319-28149-0_36|editor-last2=Simpson|editor-first2=Alastair G. B.|editor-last3=Slamovits|editor-first3=Claudio H.}}

File:Algaeconjugate.jpg

Green algae are a group of photosynthetic, eukaryotic organisms that include species with haplobiontic and diplobiontic life cycles. The diplobiontic species, such as Ulva, follow a reproductive cycle called alternation of generations in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic (having the same morphology). In haplobiontic species only the haploid generation, the gametophyte is multicellular. The fertilized egg cell, the diploid zygote, undergoes meiosis, giving rise to haploid cells which will become new gametophytes. The diplobiontic forms, which evolved from haplobiontic ancestors, have both a multicellular haploid generation and a multicellular diploid generation. Here the zygote divides repeatedly by mitosis and grows into a multicellular diploid sporophyte. The sporophyte produces haploid spores by meiosis that germinate to produce a multicellular gametophyte. All land plants have a diplobiontic common ancestor, and diplobiontic forms have also evolved independently within Ulvophyceae more than once (as has also occurred in the red and brown algae).{{cite book |last1=Trillo |first1=Inaki Ruiz |last2=Nedelcu |first2=Aurora M |date=2015 |title=Evolutionary transitions to multicellular life: Principles and mechanisms |publisher=Springer |isbn=978-94-017-9642-2 }}

Diplobiontic green algae include isomorphic and heteromorphic forms. In isomorphic algae, the morphology is identical in the haploid and diploid generations. In heteromorphic algae, the morphology and size are different in the gametophyte and sporophyte.{{cite journal |first1=Kazuhiro |last1=Bessho |first2=Yoh |last2=Iwasa |s2cid=46519857 |title=Heteromorphic and isomorphic alternations of generations in macroalgae as adaptations to a seasonal environment |journal=Evolutionary Ecology Research |date=2009 |volume=11 |pages=691–711 }}

Reproduction varies from fusion of identical cells (isogamy) to fertilization of a large non-motile cell by a smaller motile one (oogamy). However, these traits show some variation, most notably among the basal green algae called prasinophytes.{{cn|date=April 2025}}

Haploid algal cells (containing only one copy of their DNA) can fuse with other haploid cells to form diploid zygotes. When filamentous algae do this, they form bridges between cells, and leave empty cell walls behind that can be easily distinguished under the light microscope. This process is called conjugation and occurs for example in Spirogyra.{{cn|date=April 2025}}

File:Freshly harvested algae 01.jpg

Sex pheromone production is likely a common feature of green algae, although only studied in detail in a few model organisms. Volvox is a genus of chlorophytes. Different species form spherical colonies of up to 50,000 cells. One well-studied species, Volvox carteri (2,000 – 6,000 cells) occupies temporary pools of water that tend to dry out in the heat of late summer. As their environment dries out, asexual V. carteri quickly die. However, they are able to escape death by switching, shortly before drying is complete, to the sexual phase of their life cycle that leads to production of dormant desiccation-resistant zygotes. Sexual development is initiated by a glycoprotein pheromone (Hallmann et al., 1998). This pheromone is one of the most potent known biological effector molecules. It can trigger sexual development at concentrations as low as 10⁻¹⁶M.{{cite journal | vauthors = Hallmann A, Godl K, Wenzl S, Sumper M | title = The highly efficient sex-inducing pheromone system of Volvox | journal = Trends in Microbiology | volume = 6 | issue = 5 | pages = 185–9 | date = May 1998 | pmid = 9614342 | doi = 10.1016/s0966-842x(98)01234-7 }} Kirk and Kirk{{cite journal | vauthors = Kirk DL, Kirk MM | title = Heat shock elicits production of sexual inducer in Volvox | journal = Science | volume = 231 | issue = 4733 | pages = 51–4 | date = January 1986 | pmid = 3941891 | doi = 10.1126/science.3941891 | bibcode = 1986Sci...231...51K }} showed that sex-inducing pheromone production can be triggered experimentally in somatic cells by heat shock. Thus heat shock may be a condition that ordinarily triggers sex-inducing pheromone in nature.

The Closterium peracerosum-strigosum-littorale (C. psl) complex is a unicellular, isogamous charophycean alga group that is the closest unicellular relative to land plants. Heterothallic strains of different mating type can conjugate to form zygospores. Sex pheromones termed protoplast-release inducing proteins (glycopolypeptides) produced by mating-type (-) and mating-type (+) cells facilitate this process.{{cite journal | vauthors = Sekimoto H, Satoh S, Fujii T | title = Biochemical and physiological properties of a protein inducing protoplast release during conjugation in theClosterium peracerosum-strigosum-littorale complex | journal = Planta | volume = 182 | issue = 3 | pages = 348–54 | date = October 1990 | pmid = 24197184 | doi = 10.1007/BF02411384 | s2cid = 1999634 }}

The green algae, including the characean algae, have served as model experimental organisms to understand the mechanisms of the ionic and water permeability of membranes, osmoregulation, turgor regulation, salt tolerance, cytoplasmic streaming, and the generation of action potentials.{{cite book|last=Tazawa|first=Masashi | name-list-style = vanc |year=2010|volume=72|pages=5–34|chapter-url=https://books.google.com/books?id=iMxH0-q42PkC&pg=PA31 |access-date=2012-07-10|doi=10.1007/978-3-642-13145-5_1|isbn=978-3-642-13145-5|title=Progress in Botany 72 |chapter=Sixty Years Research with Characean Cells: Fascinating Material for Plant Cell Biology }}

{{Reflist|30em}}

• [https://web.archive.org/web/20060921203727/http://home.arcor.de/stefan.wic/diplomarbeit.pdf#search=%22%22stefan%20wic%22%22/ Green algae and cyanobacteria in lichens]
• [https://web.archive.org/web/20070213103838/http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html Green algae (UC Berkeley)]
• [https://web.archive.org/web/20070206081452/http://www.mbari.org/staff/conn/botany/flora/green.htm Monterey Bay green algae]

{{Plant classification}}

{{Authority control}}

Category:Green algae

Category:Paraphyletic groups