Green algae

Short description: Paraphyletic group of autotrophic eukaryotes in the clade Archaeplastida

Green algae

Stigeoclonium, a chlorophyte green alga genus
Scientific classification
(unranked):  | Archaeplastida
Kingdom:  | Plantae
Groups included

* Mesostigmatophyceae
* Spirotaenia
* Chlorokybophyceae
* Chlorophyta
* Charophyta

Cladistically included but traditionally excluded taxa

* Embryophyta

The green algae (Template:Singular: green alga) 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.[1][2][3] Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them.[2][4][5][6][7][excessive citations] 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.[8] Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.

A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in dinoflagellates of the genus Lepidodinium, euglenids and chlorarachniophytes were acquired from ingested green algae,[9] and in the latter retain a nucleomorph (vestigial nucleus). Green algae are also found symbiotically in the ciliate Paramecium, and in Hydra viridissima and in flatworms. Some species of green algae, particularly of genera Trebouxia of the class Trebouxiophyceae and Trentepohlia (class Ulvophyceae), can be found in symbiotic associations with fungi to form lichens. In general the fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus. Trentepohlia is a filamentous green alga that can live independently on humid soil, rocks or tree bark or form the photosymbiont in lichens of the family Graphidaceae. Also the macroalga Prasiola calophylla (Trebouxiophyceae) is terrestrial,[10] and Prasiola crispa, which live in the supralittoral zone, is terrestrial and can in the Antarctic form large carpets on humid soil, especially near bird colonies.[11]

## Contents

* 1 Cellular structure
* 2 Origins
* 3 Evolution and classification
* 4 Reproduction
* 4.1 Sex pheromone
* 5 Physiology
* 6 References
* 7 External links

## Cellular structure

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.[12][13] The cell walls of green algae usually contain cellulose, and they store carbohydrate in the form of starch.[14]

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[15] 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.[16] 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.[17]

## Origins

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.[18] 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).[19]

## Evolution and classification

A growth of the green seaweed Ulva 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.[20]

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.[21][20][22][23][5][24][25][26][27][28][29][30][1][excessive citations]

Viridiplantae/  |  | Prasinodermophyta |  |  |

Palmophyllophyceae (prasinophyte clade VI)

|

Prasinodermophyceae

|  | Chlorophyta |  |  |  |  |  |  |  | core Chlorophyta  |  | Chlorophytina |  |  |  |  |  |  |

Ulvophyceae

|

Chlorophyceae

Trebouxiophyceae

Chlorodendrophyceae

Pedinophyceae

Prasinophytes Clade VIIA

|  |  |

Prasinophytes Clade VIIC

|

Pycnococcaceae

Nephroselmidophyceae

|  |  |

Mamiellophyceae

|

Pyramimonadales

Streptophyta/  |  |  |  |  |

Mesostigmatophyceae

|

|  |  |

Spirotaenia

|

Chlorokybophyceae

|  |  |

Streptofilum

|

|  |  |

Klebsormidiophyceae

|

Phragmoplastophyta |  |  |

Charophyceae

|

|  |  |

Coleochaetophyceae

|

|  |  |  |  |

Zygnematophyceae

|

Mesotaeniaceae s.s.

Embryophyta (land plants)

Charophyta
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.[31]

## Reproduction

Green algae conjugating

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).[32]

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.[33]

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.

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.

### Sex pheromone

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.[34] Kirk and Kirk[35] 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.[34]

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.[36]

## Physiology

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.[37]

## References

1. ↑ 1.0 1.1 Linzhou Li; Sibo Wang; Hongli Wang; Sunil Kumar Sahu; Birger Marin; Haoyuan Li; Yan Xu; Hongping Liang et al. (22 June 2020). "The genome of Prasinoderma coloniale unveils the existence of a third phylum within green plants". Nature Ecology & Evolution 4 (9): 1220–1231. doi:10.1038/s41559-020-1221-7. PMID 32572216.
2. ↑ 2.0 2.1 "Plants". Current Biology 21 (11): R417–22. June 2011. doi:10.1016/j.cub.2011.04.021. PMID 21640897.
3. ↑ "The plant tree of life: an overview and some points of view". American Journal of Botany 91 (10): 1437–45. October 2004. doi:10.3732/ajb.91.10.1437. PMID 21652302.
4. ↑ "Charophycean Green Algae Home Page". http://www.life.umd.edu/labs/delwiche/Charophyte.html.
5. ↑ 5.0 5.1 "From algae to angiosperms-inferring the phylogeny of green plants (Viridiplantae) from 360 plastid genomes". BMC Evolutionary Biology 14: 23. February 2014. doi:10.1186/1471-2148-14-23. PMID 24533922.
6. ↑ "The Evolutionary Origin of a Terrestrial Flora" (in en). Current Biology 25 (19): R899–910. October 2015. doi:10.1016/j.cub.2015.08.029. PMID 26439353.
7. ↑ "Estimating the timing of early eukaryotic diversification with multigene molecular clocks". Proceedings of the National Academy of Sciences of the United States of America 108 (33): 13624–9. August 2011. doi:10.1073/pnas.1110633108. PMID 21810989. Bibcode: 2011PNAS..10813624P.
8. ↑ "How many species of algae are there?". Journal of Phycology 48 (5): 1057–63. October 2012. doi:10.1111/j.1529-8817.2012.01222.x. PMID 27011267.
9. ↑ Jackson, Christopher; Knoll, Andrew H.; Chan, Cheong Xin; Verbruggen, Heroen (2018). "Plastid phylogenomics with broad taxon sampling further elucidates the distinct evolutionary origins and timing of secondary green plastids". Scientific Reports 8 (1): 1523. doi:10.1038/s41598-017-18805-w. PMID 29367699. Bibcode: 2018NatSR...8.1523J.
10. ↑ Holzinger, A.; Herburger, K.; Blaas, K.; Lewis, L. A.; Karsten, U. (2017). "The terrestrial green macroalga Prasiola calophylla (Trebouxiophyceae, Chlorophyta): Ecophysiological performance under water-limiting conditions". Protoplasma 254 (4): 1755–1767. doi:10.1007/s00709-016-1068-6. PMID 28066876.
11. ↑ Carvalho, Evelise L.; MacIel, Lucas F.; MacEdo, Pablo E.; Dezordi, Filipe Z.; Abreu, Maria E. T.; Victória, Filipe de Carvalho; Pereira, Antônio B.; Boldo, Juliano T. et al. (2018). "De novo Assembly and Annotation of the Antarctic Alga Prasiola crispa Transcriptome". Frontiers in Molecular Biosciences 4: 89. doi:10.3389/fmolb.2017.00089. PMID 29359133.
12. ↑ Burrows 1991. Seaweeds of the British Isles. Volume 2 Natural History Museum, London. ISBN:0-565-00981-8
13. ↑ Algae An introduction to phycology. Cambridge: Cambridge University Press. 1995. ISBN 978-0-521-30419-1. https://books.google.com/books?id=xuUoiFesSHMC.
14. ↑ Plant systematics, a phylogenetic approach.. Sunderland Mass.: Sinauer Associates Inc.. 2002. pp. 156. ISBN 978-0-87893-403-4. https://archive.org/details/plantsystematics0002unse/page/156.
15. ↑ "Letter to the editor". Toxicology and Applied Pharmacology 112 (2): 331–332. 1992. doi:10.1016/0041-008x(92)90204-6. PMID 1539170.
16. ↑ "Cell division in eucaryotic algae". BioScience 26 (7): 445–450. 1976. doi:10.2307/1297481.
17. ↑ 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
18. ↑ "The endosymbiotic origin, diversification and fate of plastids". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 365 (1541): 729–48. March 2010. doi:10.1098/rstb.2009.0103. PMID 20124341.
19. ↑ "Diversity and Evolution of Algae". Genomic Insights into the Biology of Algae. Advances in Botanical Research. 64. 2012. pp. 55–86. doi:10.1016/B978-0-12-391499-6.00002-5. ISBN 9780123914996.
20. ↑ 20.0 20.1 Leliaert, Frederik; Smith, David R.; Moreau, Hervé; Herron, Matthew D.; Verbruggen, Heroen; Delwiche, Charles F.; De Clerck, Olivier (2012). "Phylogeny and Molecular Evolution of the Green Algae". Critical Reviews in Plant Sciences 31: 1–46. doi:10.1080/07352689.2011.615705. https://frederikleliaert.files.wordpress.com/2013/05/2012_leliaert_crps.pdf.
21. ↑ "Green algae and the origin of land plants". American Journal of Botany 91 (10): 1535–56. October 2004. doi:10.3732/ajb.91.10.1535. PMID 21652308.
22. ↑ "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". Protist 163 (5): 778–805. September 2012. doi:10.1016/j.protis.2011.11.004. PMID 22192529.
23. ↑ "Origin of land plants revisited in the light of sequence contamination and missing data". Current Biology 22 (15): R593–4. August 2012. doi:10.1016/j.cub.2012.06.013. PMID 22877776.
24. ↑ "Chloroplast phylogenomic analyses reveal the deepest-branching lineage of the Chlorophyta, Palmophyllophyceae class. nov". Scientific Reports 6: 25367. May 2016. doi:10.1038/srep25367. PMID 27157793. Bibcode: 2016NatSR...625367L.
25. ↑ Lecointre, Guillaume; Guyader, Hervé Le (2006) (in en). The Tree of Life: A Phylogenetic Classification. Harvard University Press. ISBN 9780674021839. https://books.google.com/books?id=S4LxB9MRdzMC&pg=PA158.
26. ↑ "Early photosynthetic eukaryotes inhabited low-salinity habitats". Proceedings of the National Academy of Sciences of the United States of America 114 (37): E7737–E7745. September 2017. doi:10.1073/pnas.1620089114. PMID 28808007. Bibcode: 2017PNAS..114E7737S.
27. ↑ "Plastid phylogenomic analysis of green plants: A billion years of evolutionary history". American Journal of Botany 105 (3): 291–301. March 2018. doi:10.1002/ajb2.1048. PMID 29603143.
28. ↑ "Ancestral chloroplast genome in Mesostigma viride reveals an early branch of green plant evolution" (in En). Nature 403 (6770): 649–52. February 2000. doi:10.1038/35001059. PMID 10688199. Bibcode: 2000Natur.403..649L.
29. ↑ Riediger, Matthias; Hihara, Yukako; Hess, Wolfgang R. (2018-06-01). "From cyanobacteria and algae to land plants: The RpaB/Ycf27 regulatory network in transition" (in en). Perspectives in Phycology 5 (1): 13–25. doi:10.1127/pip/2018/0078. ISSN 2198-011X.
30. ↑ Turmel, Monique; Lemieux, Claude (2018), "Evolution of the Plastid Genome in Green Algae", Advances in Botanical Research (Elsevier): pp. 157–193, doi:10.1016/bs.abr.2017.11.010, ISBN 9780128134573
31. ↑ Cook, Martha E.; Graham, Linda E. (2017). "Chlorokybophyceae, Klebsormidiophyceae, Coleochaetophyceae". in Archibald, John M.. Handbook of the Protists. Springer International Publishing. pp. 185–204. doi:10.1007/978-3-319-28149-0_36. ISBN 9783319281476.
32. ↑ Trillo, Inaki Ruiz; Nedelcu, Aurora M (2015). Evolutionary transitions to multicellular life: Principles and mechanisms. Springer. ISBN 978-94-017-9642-2.
33. ↑ Bessho, Kazuhiro; Iwasa, Yoh (2009). "Heteromorphic and isomorphic alternations of generations in macroalgae as adaptations to a seasonal environment". Evolutionary Ecology Research 11: 691–711.
34. ↑ 34.0 34.1 "The highly efficient sex-inducing pheromone system of Volvox". Trends in Microbiology 6 (5): 185–9. May 1998. doi:10.1016/s0966-842x(98)01234-7. PMID 9614342.
35. ↑ "Heat shock elicits production of sexual inducer in Volvox". Science 231 (4733): 51–4. January 1986. doi:10.1126/science.3941891. PMID 3941891. Bibcode: 1986Sci...231...51K.
36. ↑ "Biochemical and physiological properties of a protein inducing protoplast release during conjugation in theClosterium peracerosum-strigosum-littorale complex". Planta 182 (3): 348–54. October 1990. doi:10.1007/BF02411384. PMID 24197184.
37. ↑ Tazawa, Masashi (2010). "Sixty Years Research with Characean Cells: Fascinating Material for Plant Cell Biology". Progress in Botany 72. 72. pp. 5–34. doi:10.1007/978-3-642-13145-5_1. ISBN 978-3-642-13145-5. https://books.google.com/books?id=iMxH0-q42PkC&pg=PA31. Retrieved 2012-07-10.

## External links

* Green algae and cyanobacteria in lichens
* Green algae (UC Berkeley)
* Monterey Bay green algae

* v
* t
* e

Classification of Archaeplastida / Plantae sensu lato

Domain
Archaea
Bacteria
Eukaryota
(Supergroup
Plant
Hacrobia
Heterokont
Alveolata
Rhizaria
Excavata
Amoebozoa
Opisthokonta

Animal
Fungi)

Rhodophyta
(red algae)|

* Cyanidiophyceae
* Porphyridiophyceae
* Compsopogonophyceae
* Stylonematophyceae
* Rhodellophyceae
* Bangiophyceae
* Florideophyceae

Glaucocystophyta
(glaucophytes)|

* Glaucocystophyceae
* Glaucocystis
* Cyanophora
* Gloeochaete

Viridiplantae
(green algae,
& land plants)|

| M+C+S|

* Mesostigmatophyceae
* Chlorokybophyceae
* Spirotaenia

|

C+S|

| Chlorophyta
(prasinophytes)|

* Mamiellophyceae
* Nephrophyceae
* Palmophyllales
* Prasinophyceae
* Pseudoscourfieldiales
* Pyramimonadophyceae
* Scourfieldiales
* Pedinophyceae
* Chlorodendrophyceae
* UTC clade
* Ulvophyceae
* Trebouxiophyceae
* Chlorophyceae

|

Streptophyta
(charophytes,
& land plants)|

* Klebsormidiophyceae

Phragmo-
plastophyta|

* Charophyceae
* Coleochaetophyceae
* Zygnematophyceae
* Mesotaeniaceae

Embryophyta
(land plants)|

| Bryophytes
(non-vascular)|

* Marchantiophyta
* Anthocerotophyta
* Bryophyta "Moss"
* †Horneophytopsida

|

Tracheophyta
(vascular)|

| Lycopodiophyta
(microphylls)|

* †Zosterophyllopsida
* †Sawdoniales
* Isoetopsida
* Lycopodiopsida

|

Euphyllophyta
(megaphylls)|

| Polypodiopsida
(ferns)|

* †Cladoxylopsida
* †Stauropteridales
* †Zygopteridales
* Equisetidae
* Ophioglossidae
* Marattiidae
* Polypodiidae

|

Spermatophyta
(seed plants)|

* †Seed ferns
* Gymnosperms
* Gnetopsida
* Pinopsida
* Cycadopsida
* Ginkgoopsida
* Angiosperms or flowering plants
* Amborellales
* Nymphaeales
* Austrobaileyales
* Magnoliids
* Monocots
* Eudicots

Other|

* †Trimerophytopsida
* †Progymnosperm

Other|

* †Rhyniopsida

† = extinct. See also the list of plant orders.

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