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 species in the group varies from about 14 to 26. Together with the red algae (Rhodophyta) and the green algae plus land plants (

Viridiplantae Viridiplantae (literally "green plants") are a clade of eukaryotic organisms that comprise approximately 450,000–500,000 species and play important roles in both terrestrial and aquatic ecosystems. They are made up of the green algae, which ar ...

or Chloroplastida), they form the

Archaeplastida The Archaeplastida (or kingdom Plantae '' sensu lato'' "in a broad sense"; pronounced /ɑːrkɪ'plastɪdə/) are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor gr ...

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

Characteristics

The plastids of glaucophytes are known as 'muroplasts', 'cyanoplasts', or 'cyanelles'. 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 peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ba ...

layer, believed to be a relic of the

endosymbiotic An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...

origin of plastids from cyanobacteria. Glaucophytes contain the photosynthetic pigment chlorophyll a. Along with red algae and cyanobacteria, they harvest light via

phycobilisome Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes. It was lost in the plastids of green algae / plants (chloroplasts). General structure Phycobilisomes are protein complexes (up to 6 ...

s, structures consisting largely of phycobiliproteins. The green algae and

land plant The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...

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 ...

. 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 with flat

cristae A crista (; plural 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 fo ...

, 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.

Phylogeny

Together with red algae and

( green algae and

land plants The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...

), glaucophytes form the

– a group of plastid-containing organisms that may share a unique common ancestor that established an

association with a

cyanobacterium 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 ...

. 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'' – 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 ,

AlgaeBase AlgaeBase is a global species database of information on all groups of algae, both marine and freshwater, as well as sea-grass. History AlgaeBase began in March 1996, founded by Michael Guiry. Text was copied from this source, which is avail ...

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 Chlorococcales is a formerly recognized order of green algae in the class Chlorophyceae. , the type family Chlorococcaceae was placed in the order Chlamydomonadales. Conventionally, many groups of coccoid green algae were lumped in the order Ch ...

References

{{Taxonbar, from=Q131116 Algal taxonomy Archaeplastida