Glaucophyte

{{Short description|Division of algae}} {{Automatic taxobox | name = Glaucophyta | image = Glaucocystis sp.jpg | image_caption = ''Glaucocystis'' sp. | parent_authority = Skuja, 1954<ref name="Skuja 1954">Skuja, A. (1954). III. Abteilung: Glaucophyta. In: ''A. Engler's Syllabus der Pflanzenfamilien: mit besonderer Berücksichtigung der Nutzpflanzen nebst einer Übersicht über die Florenreiche und Florengebiete der Erde'', 12th ed. I Band ''Allgemeiner Teil Bakterien bis Gymnospermen''. (Melchior, H. & Werdermann, E. Eds), pp. 56–57. Berlin-Nikolassee: Borntraeger.</ref> | taxon = Glaucophyceae | authority = Bohlin, 1901 | subdivision_ranks = Orders | subdivision_ref = <ref>Guiry, M.D. & Guiry, G.M. 2025. ''AlgaeBase''. World-wide electronic publication, University of Galway. <nowiki>https://www.algaebase.org</nowiki>; searched on 8 January 2025.</ref> | subdivision = *Glaucocystales *Gloeochaetales | synonyms = Glaucocystophyta Kies and Kremer, 1986 }}

The '''glaucophytes''', also known as '''glaucocystophytes''' or '''glaucocystids''', are a small group of unicellular algae found in freshwater and moist terrestrial environments,<ref name="keeling">{{cite journal |journal =American Journal of Botany |year=2004 |volume=91 | pages=1481–1493 | title=Diversity and evolutionary history of plastids and their hosts |last=Keeling |first=Patrick J. | doi=10.3732/ajb.91.10.1481 |issue=10 |pmid=21652304 |doi-access=free |bibcode=2004AmJB...91.1481K }}</ref><ref>[https://books.google.com/books?id=lE6r5q5op94C&dq=%22Glaucophyta+%28also+known+as+Glaucocystophyta%29+is+a+small+and+inconspicuous+group+of+unicellular+algae+found+in+freshwater+and+terrestrial+environments%22&pg=PA74 Genomic Insights Into the Biology of Algae]</ref> less common today than they were during the Proterozoic.<ref name="Cruzan 2018">{{cite book |last=Cruzan |first=Mitchell B. |title=Evolutionary Biology |publisher=Oxford University Press |year=2018 |isbn=978-0-19-088268-6 |page=20 }}</ref> The stated number of species in the group varies from about 14 to 26.<ref name=FiguJackReye19/><ref>[http://jcs.biologists.org/content/131/2/jcs203414 The monoplastidic bottleneck in algae and plant evolution | Journal of Cell Science]</ref><ref>{{AlgaeBase taxon |name=Glaucophyta |id=4301 |access-date=2022-02-28}}</ref> Together with the much larger sister taxa Rhodophyta (red algae) and Viridiplantae/Chloroplastida (green algae and land plants), they form the primary algae clade Archaeplastida.

The glaucophytes are of interest to biologists studying the evolution of chloroplasts as they may be similar to the ancestral algal type that led to the red algae and green plants, i.e. glaucophytes may be basal archaeplastids.<ref name="keeling" /><ref>{{cite journal |doi = 10.1371/journal.pone.0002621 |year=2008 |last1=Kim |first1=Eunsoo |last2=Graham |first2=Linda E. |title=EEF2 Analysis Challenges the Monophyly of Archaeplastida and Chromalveolata |volume=3 |issue=7 |article-number=e2621 |pmid=18612431 | pmc=2440802 |journal=PLoS ONE |bibcode = 2008PLoSO...3.2621K |editor1-last=Redfield |editor1-first=Rosemary Jeanne |editor1-link=Rosemary Redfield |doi-access=free }}</ref><ref name=FiguJackReye19/>

Unlike red and green algae, glaucophytes only have asexual reproduction.<ref name="Walker 2012">{{cite book |last=Walker |first=Timothy |title=Plants: A Very Short Introduction |publisher=Oxford University Press |year=2012 |isbn=978-0-19-958406-2 |page=10}}</ref>

== Reproduction == Unlike red and green algae, glaucophytes reproduce exclusively through asexual means. They undergo open mitosis without centrioles, a trait shared with other basal eukaryotes. Reproductive modes include binary fission, zoospore formation, and autosporulation. For example, ''Cyanophora paradoxa'' divides longitudinally, producing two daughter cells, each inheriting a single cyanelle. Species of ''Glaucocystis'' reproduce via non-motile autospores. To date, there is no evidence of sexual reproduction in glaucophytes.<ref>Jackson, C. (2015). The Glaucophyta: The blue-green plants in a nutshell. ''Acta Societatis Botanicorum Poloniae'' 84(4): 439–443. https://doi.org/10.5586/asbp.2015.049</ref>

==Characteristics== The plastids of glaucophytes are known as 'muroplasts',<ref name="Wise—Plastid diversity">{{cite book |editor1-last=Wise |editor1-first=Robert R. |editor2-last=Hoober |editor2-first=J. Kenneth |title=The structure and function of plastids |year=2006 |publisher=Springer |location=Dordrecht |isbn=978-1-4020-4061-0 |pages=3–21 |url=http://www.uwosh.edu/biology/faculty-and-staff/faculty/wise/publications/wise-the-diversity-of-plastid |archive-date=2016-03-08 |access-date=2019-03-12 |archive-url=https://web.archive.org/web/20160308205912/http://www.uwosh.edu/biology/faculty-and-staff/faculty/wise/publications/wise-the-diversity-of-plastid }}</ref> 'cyanoplasts', or 'cyanelles'. Unlike the plastids in other organisms, they have a peptidoglycan layer, believed to be a relic of the endosymbiotic origin of plastids from cyanobacteria.<ref name="keeling" /><ref name="Miyagishima">{{cite journal |doi=10.1186/1471-2229-14-57 |pmid=24602296 |pmc=4015805 |title=DipM is required for peptidoglycan hydrolysis during chloroplast division |journal=BMC Plant Biology |volume=14 |page=57 |year=2014 |last1=Miyagishima |first1=Shin-ya |last2=Kabeya |first2=Yukihiro |last3=Sugita |first3=Chieko |last4=Sugita |first4=Mamoru |last5=Fujiwara |first5=Takayuki |issue=1 |doi-access=free |bibcode=2014BMCPB..14...57M }}</ref> This peptidoglycan layer plays a functional role in plastid division and is considered molecular evidence of their cyanobacterial ancestry.<ref>{{Cite journal |last1=Oldach |first1=Klaus H |last2=Peck |first2=David M |last3=Nair |first3=Ramakrishnan M |last4=Sokolova |first4=Maria |last5=Harris |first5=John |last6=Bogacki |first6=Paul |last7=Ballard |first7=Ross |date=2014 |title=Genetic analysis of tolerance to the root lesion nematode Pratylenchus neglectus in the legume Medicago littoralis |journal=BMC Plant Biology |volume=14 |issue=1 |page=100 |doi=10.1186/1471-2229-14-100 |doi-access=free |pmid=24742262 |pmc=4021308 |bibcode=2014BMCPB..14..100O |issn=1471-2229}}</ref> Glaucophytes contain the photosynthetic pigment chlorophyll a.<ref name="keeling" /> Along with red algae<ref name="keeling" /> and cyanobacteria, they harvest light via phycobilisomes, structures consisting largely of phycobiliproteins. The green algae and land plants have lost that pigment.<ref name="Skuja 1948">Skuja, A. (1948). Taxonomie des Phytoplanktons einiger Seen in Uppland, Schweden. Symbolae Botanicae Upsalienses 9(3): 1-399.{{AlgaeBase taxon|id=4301|name=Glaucophyta}}</ref> Like red algae, and in contrast to green algae and plants, glaucophytes store fixed carbon in the cytosol.<ref name="ball_2011">{{cite journal |last1=Ball |first1=S. |last2=Colleoni |first2=C.|last3=Cenci |first3=U. |last4=Raj |first4=J. N. |last5=Tirtiaux |first5=C. |title=The evolution of glycogen and starch metabolism in eukaryotes gives molecular clues to understand the establishment of plastid endosymbiosis |journal=Journal of Experimental Botany |date=10 January 2011 |volume=62 |issue=6 |pages=1775–1801 |doi=10.1093/jxb/erq411 |pmid=21220783 |doi-access=free}}</ref>

This cytosolic carbon fixation, rather than fixation within plastids, is considered a retained ancestral trait. Glaucophyte phycobilisomes are composed primarily of phycocyanin and allophycocyanin, two key pigments also present in cyanobacteria. These pigments allow absorption of light at wavelengths that chlorophyll cannot, enhancing light harvesting in low-light aquatic environments.<ref>{{Cite journal |last=Ludwig-Müller |first=Jutta |date=2011-02-09 |title=Auxin conjugates: their role for plant development and in the evolution of land plants |journal=Journal of Experimental Botany |volume=62 |issue=6 |pages=1757–1773 |doi=10.1093/jxb/erq412 |pmid=21307383 |issn=1460-2431}}</ref> Studies of endosymbiotic gene transfer (EGT) suggest that several genes originally encoded in cyanobacterial ancestors have been relocated to the nuclear genome in glaucophytes, reflecting early stages of plastid-host genomic integration.<ref>Nowack, E. C. M., et al. (2008). Gene transfers from diverse bacteria compensate for reductive genome evolution in the chromatophore of Paulinella chromatophora. ''PNAS'' 105(5): 16782–16787. https://doi.org/10.1073/pnas.0809772105</ref> The evolution of glycogen and starch metabolism in eukaryotes gives molecular clues to understand the establishment of plastid endosymbiosis.{{cn|date=July 2025}}

The most early-diverging genus is ''Cyanophora'', which only has one or two plastids. When there are two, they are semi-connected.<ref name="de Vries Gould 2017 p. ">{{cite journal | last1=de Vries | first1=Jan | last2=Gould | first2=Sven B. | title=The monoplastidic bottleneck in algae and plant evolution | journal=Journal of Cell Science | publisher=The Company of Biologists | date=2017-01-01 | volume=131 | issue=2 | issn=1477-9137 | doi=10.1242/jcs.203414 | article-number=jcs203414 | pmid=28893840 | doi-access=free }}</ref>

Glaucophytes have mitochondria with flat cristae, and undergo open mitosis without centrioles. Motile forms have two unequal flagella, which may have fine hairs and are anchored by a multilayered system of microtubules, both of which are similar to forms found in some green algae.<ref name="Skuja 1948"/>

[[File:2024 Glaucophyte Numbered.svg|thumb|center|upright=2|{{center|'''Representation of a glaucophyte'''}}{{ordered list|Anterior flagellum (with hairs)| Mucocyst, discharges a mucous mass sometimes used in cyst formation| Plate| Plate vesicle| Starch granule| Furrow| Anterior folds| Basal body| Contractile vacuole, regulates the quantity of water inside a cell| Golgi apparatus; modifies proteins and sends them out of the cell| Plastid membranes (2, primary)| Peptidoglycan, a polysaccharide layer surrounding the cytoplasmic membrane| Central body| Thylakoids, site of the light-dependent reactions of photosynthesis| Phycobilisome| Nucleolus| Nucleus| Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell| Mitochondrion, creates ATP (energy) for the cell, (flat cristae)| Posterior flagellum}}]] {{anchor|muroplast}}

== Phylogeny ==

=== External ===

Together with red algae and Viridiplantae (green algae and land plants), glaucophytes form the Archaeplastida – a group of plastid-containing organisms that may share a unique common ancestor that established an endosymbiotic association with a cyanobacterium. The relationship among the three groups remains uncertain, although it is most likely that glaucophytes diverged first:<ref name=FiguJackReye19/>

{{clade |label1=Archaeplastida |1={{clade |1='''Glaucophyta''' |2={{clade |1=Red algae |2=Viridiplantae }} }} }}

The alternative, that glaucophytes and red algae form a clade, has been shown to be less plausible, but cannot be ruled out.<ref name=FiguJackReye19/>

=== Internal ===

The internal phylogeny of the glaucophytes and the number of genera and species varies considerably among taxonomic sources. A phylogeny of the Glaucophyta published in 2017 divided the group into three families, and includes five genera:<ref>{{cite book |last1=Price |first1=Dana C. |last2=Steiner |first2=Jürgen M. |last3=Yoon |first3=Hwan Su |last4=Bhattacharya |first4=Debashish |last5=Löffelhardt |first5=Wolfgang |date=2016 |doi=10.1007/978-3-319-32669-6_42-1 |contribution=Glaucophyta |title=Handbook of the Protists |pages=1–65 |isbn=978-3-319-32669-6 }}</ref> {{Clade |label1='''Glaucophyta''' |1={{Clade |label1=Cyanophoraceae |1=''Cyanophora'' |2={{Clade |label1=Gloeochaetaceae |1={{Clade |1=''Cyanoptyche'' |2=''Gloeochaete'' }} |label2=Glaucocystidaceae |2={{Clade |1=''Glaucocystopsis'' |2=''Glaucocystis'' }} }} }} }}

=== Taxonomy === [[File:Woelfib_cyanphoraparadoxa_teilungsfigur_1_0632002_img_54414492_ude_20131024233254_small.jpg|thumb|''Cyanophora paradoxa'']]

A 2019 list of the described glaucophyte species has the same three subdivisions, treated as orders, but includes a further five unplaced possible species, producing a total of between 14 and 19 possible species.<ref name=FiguJackReye19>{{Citation |mode=cs1 |last1=Figueroa-Martinez |first1=Francisco |last2=Jackson |first2=Christopher |last3=Reyes-Prieto |first3=Adrian |date=2019 |title=Plastid Genomes from Diverse Glaucophyte Genera Reveal a Largely Conserved Gene Content and Limited Architectural Diversity |journal=Genome Biology and Evolution |volume=11 |issue=1 |pages=174–188 |doi=10.1093/gbe/evy268 |pmid=30534986 |pmc=6330054 }}</ref> * Order Cyanophorales ** Genus ''Cyanophora'' – 5–6 species * Order Glaucocystales ** Genus ''Glaucocystis'' – 7–8 species * Order Gloeochaetales ** ''Cyanoptyche'' – 1 species ** ''Gloeochaete'' – 1 species * Other possible species ** ?''Archaeopsis monococca'' Skuja ** ?''Chalarodora azurea'' Pascher ** ?''Glaucocystopsis africana'' Bourrelly ** ?''Peliaina cyanea'' Pascher ** ?''Strobilomonas cyaneus'' Schiller

{{As of|2026|May}}, AlgaeBase divided glaucophytes into only two groups, placing ''Cyanophora'' in Glaucocystales rather than Cyanophorales (however the entry was dated 2011).<ref name=AB_g44133>{{AlgaeBase genus|name=Cyanophora|id=44133|access-date=2022-03-01}}</ref> AlgaeBase included a total of 25 species in eight genera:<ref name=AB_t4301>{{AlgaeBase taxon|name=Glaucophyta|id=4301|access-date=2026-05-21}}</ref> * Glaucocystales ** ''Chalarodora'' Pascher – 1 species ** ''Cyanophora'' Korshikov – 6 species ** ''Glaucocystis'' Itzigsohn – 13 species ** ''Glaucocystopsis'' Bourrelly – 1 species ** ''Peliaina'' Pascher – 1 species ** ''Strobilomonas'' Schiller – 1 species * Gloeochaetales ** ''Cyanoptyche'' Pascher – 1 species ** ''Gloeochaete'' Lagerheim – 1 species

None of the species of Glaucophyta is particularly common in nature.<ref name="keeling" />

The glaucophytes were considered before as part of family Oocystaceae, in the order Chlorococcales.<ref>{{Cite web|url=http://cfb.unh.edu/phycokey/Choices/Glaucophyceae/GLAUCOCYSTIS/Glaucocystis_key.html|title=Phycokey - Glaucocystis}}</ref>

==References==

Category:Algal taxonomy Category:Glaucophyta