The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular
algae
Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
found in freshwater and moist terrestrial environments,
less common today than they were during the
Proterozoic
The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...
.
The stated number of species in the group varies from about 14 to 26.
[ Together with the red algae (Rhodophyta) and the ]green algae
The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...
plus land plants (Viridiplantae
Viridiplantae (; kingdom Plantae '' sensu stricto'') is a clade of around 450,000–500,000 species of eukaryotic organisms, most of which obtain their energy by photosynthesis. The green plants are chloroplast-bearing autotrophs that play impo ...
or Chloroplastida), they form the Archaeplastida
The Archaeplastida (or kingdom Plantae '' sensu lato'' "in a broad sense"; pronounced ) are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes. It als ...
.
The glaucophytes are of interest to biologists studying the evolution of chloroplast
A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
s as they may be similar to the original algal type that led to the red algae and green plants, i.e. glaucophytes may be basal Archaeplastida.[
Unlike red and green algae, glaucophytes only have ]asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...
.
Reproduction
Unlike red and green algae, glaucophytes only have asexual reproduction. 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.
Characteristics
The plastid
A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria.
Examples of plastids include chloroplasts ...
s of glaucophytes are known as 'muroplast
The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of speci ...
s', 'cyanoplasts', or 'cyanelle
A plastid is a membrane-bound organelle found in the cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria.
Examples of plastids include chloroplasts (used for photo ...
s'. Unlike the plastids in other organisms, they have a peptidoglycan
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like layer (sacculus) that surrounds the bacterial cytoplasmic membrane. The sugar component consists of alternating ...
layer, believed to be a relic of the endosymbiotic
An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), which live in the root ...
origin of plastids from cyanobacteria
Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...
.This peptidoglycan layer plays a functional role in plastid division and is considered molecular evidence of their cyanobacterial ancestry. Glaucophytes contain the photosynthetic pigment 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, and it is a poor absorber of green and near-green portions of the spectrum. Chlorop ...
. Along with red algae
Red algae, or Rhodophyta (, ; ), make up one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest Phylum, phyla of algae, containing over 7,000 recognized species within over 900 Genus, genera amidst ongoing taxon ...
and cyanobacteria
Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...
, they harvest light via phycobilisome
Phycobilisomes are light-harvesting antennae that transmit the energy of harvested photons to photosystem II and photosystem I in cyanobacteria and in the chloroplasts of red algae and glaucophytes. They were lost during the evolution of the ...
s, structures consisting largely of phycobiliprotein
Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae (rhodophytes, cryptomonads, glaucocystophytes). They capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are ...
s. The green algae
The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...
and land plant
The embryophytes () are a clade of plants, also known as Embryophyta (Plantae ''sensu strictissimo'') () or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophyt ...
s have lost that pigment.[Skuja, A. (1948). Taxonomie des Phytoplanktons einiger Seen in Uppland, Schweden. Symbolae Botanicae Upsalienses 9(3): 1-399.] Like red algae, and in contrast to green algae and plants, glaucophytes store fixed carbon in the cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
.
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.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.The evolution of glycogen and starch metabolism in eukaryotes gives molecular clues to understand the establishment of plastid endosymbiosis.
The most early-diverging genus is ''Cyanophora
''Cyanophora'' is a genus of glaucophytes, a group of rare but evolutionarily significant freshwater microalgae.
It includes the following species:
* '' Cyanophora biloba''
* '' Cyanophora cuspidata''
* '' Cyanophora kugrensii''
* '' Cyanophora ...
'', which only has one or two plastids. When there are two, they are semi-connected.
Glaucophytes have mitochondria
A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...
with flat cristae
A crista (; : cristae) is a fold in the inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of surface area for che ...
, and undergo open mitosis
Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...
without centriole
In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers ( Pinophyta), flowering plants ( angiosperms) and most fungi, an ...
s. Motile forms have two unequal flagella
A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...
, which may have fine hairs and are anchored by a multilayered system of microtubule
Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...
s, both of which are similar to forms found in some green algae.[
]
Phylogeny
External
Together with red algae
Red algae, or Rhodophyta (, ; ), make up one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest Phylum, phyla of algae, containing over 7,000 recognized species within over 900 Genus, genera amidst ongoing taxon ...
and Viridiplantae
Viridiplantae (; kingdom Plantae '' sensu stricto'') is a clade of around 450,000–500,000 species of eukaryotic organisms, most of which obtain their energy by photosynthesis. The green plants are chloroplast-bearing autotrophs that play impo ...
(green algae
The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...
and land plants
The embryophytes () are a clade of plants, also known as Embryophyta (Plantae ''sensu strictissimo'') () or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophy ...
), glaucophytes form the Archaeplastida
The Archaeplastida (or kingdom Plantae '' sensu lato'' "in a broad sense"; pronounced ) are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes. It als ...
– a group of plastid
A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria.
Examples of plastids include chloroplasts ...
-containing organisms that may share a unique common ancestor that established an endosymbiotic
An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), which live in the root ...
association with a cyanobacterium
Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteria' ...
. The relationship among the three groups remains uncertain, although it is most likely that glaucophytes diverged first:[
The alternative, that glaucophytes and red algae form a clade, has been shown to be less plausible, but cannot be ruled out.][
]
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:
Taxonomy
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.
*Order Cyanophorales
**Genus ''Cyanophora
''Cyanophora'' is a genus of glaucophytes, a group of rare but evolutionarily significant freshwater microalgae.
It includes the following species:
* '' Cyanophora biloba''
* '' Cyanophora cuspidata''
* '' Cyanophora kugrensii''
* '' Cyanophora ...
'' – 5–6 species
A recent study by Takahashi et al. (2023) used both morphological and molecular data to distinguish five distinct species within the genus Cyanophora, confirming species boundaries and supporting the utility of combined phylogenetic analysis.
*Order Glaucocystales
The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of speci ...
**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
, AlgaeBase
AlgaeBase is a global species database of information on all groups of algae, both seaweed, marine and freshwater algae, freshwater, as well as sea-grass.
History
AlgaeBase began in March 1996, founded by Michael D. Guiry, Michael Guiry. Text ...
divided glaucophytes into only two groups, placing ''Cyanophora'' in Glaucocystales rather than Cyanophorales (however the entry was dated 2011). AlgaeBase included a total of 26 species in nine genera:
*Glaucocystales
**''Chalarodora'' Pascher – 1 species
**''Corynoplastis'' Yokoyama, J.L.Scott, G.C.Zuccarello, M.Kajikawa, Y.Hara & J.A.West – 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.
The glaucophytes were considered before as part of family Oocystaceae
Oocystaceae is a family (biology), family of green algae, in the class Trebouxiophyceae. Molecular phylogenetic studies mostly (but not always) place the family in the order Chlorellales, as sister to Chlorellaceae. The Type (biology), type genus ...
, in the order Chlorococcales
Chlorococcales is a formerly recognized Order (biology), order of green algae in the Class (biology), class Chlorophyceae. , the type family Chlorococcaceae was placed in the order Chlamydomonadales.
Conventionally, many groups of coccoid green ...
.
References
{{Taxonbar, from=Q131116
Algal taxonomy