The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

found in freshwater and moist terrestrial environments, less common today than they were during the

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

. 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 (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 ...

plus land plants ( Viridiplantae or Chloroplastida), they form the Archaeplastida. However, the relationships among the red algae, green algae and glaucophytes are unclear, in large part due to limited study of the glaucophytes. The glaucophytes are of interest to biologists studying the development of

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s because some studies suggest they may be similar to the original algal type that led to green plants and red algae in that glaucophytes may be

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

Archaeplastida. Unlike red and green algae, glaucophytes only have asexual reproduction.

Characteristics

The

plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosy ...

s of glaucophytes are known as 'muroplasts', '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 Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

. Glaucophytes contain the photosynthetic pigment chlorophyll a. Along with

red algae Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

and

, they harvest light via phycobilisomes, 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

and land plants 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 most basal-branching genus is 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 Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

with flat cristae, and undergo open

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

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, and a ...

s. Motile forms have two unequal

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

, 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 nm and have an inner diameter between 11 an ...

s, both of which are similar to forms found in some green algae.

Phylogeny

Together with

and Viridiplantae (

and land plants), glaucophytes form the Archaeplastida – a group of

-containing organisms that may share a unique common ancestor that established an endosymbiotic association with a cyanobacterium. The relationship among the three groups remained uncertain , although studies suggest 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.

Classification

The internal classification of the glaucophytes and the number of genera and species varied considerably among taxonomic sources, . A phylogeny of the Glaucocystophyceae published in 2017 divides the group into three families, and includes five genera: A list of the described glaucophyte species first published in 2018 has the same three subdivisions, treated as orders, but includes a further five unplaced possible species, producing a total of 14–19 possible species. *Order Cyanophorales **Genus ''

Cyanophora 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 spe ...

'' – 5–6 species *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 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 ...

'' – 7–8 species *Order Gloeochaetales **'' Cyanoptyche'' – 1 species **''

Gloeochaete 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 spe ...

'' – 1 species *Other possible species **?'' Archaeopsis monococca'' Skuja **?'' Chalarodora azurea'' Pascher **?'' Glaucocystopsis africana'' Bourrelly **?'' Peliaina cyanea'' Pascher **?'' Strobilomonas cyaneus'' Schiller , AlgaeBase 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, in the order Chlorococcales.

References

{{Taxonbar, from=Q131116 Algal taxonomy Archaeplastida