The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of freshwater microscopic algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

. Together with the red algae

Red algae

The red algae are one of the oldest groups of eukaryotic algae, and also one of the largest, with about 5,000–6,000 species  of mostly multicellular, marine algae, including many notable seaweeds...

 (Rhodophyta) and green algae plus land plants (Viridiplantae

Viridiplantae

Viridiplantae are a clade comprising the green algae and land plants.In some classification systems they have been treated as a kingdom, under various names, e.g. Viridiplantae, Chlorobionta, or simply Plantae, the latter expanding the traditional Plant Kingdom to include the green algae...

 or Chloroplastida), they form the Archaeplastida

Archaeplastida

The Archaeplastida are a major group of eukaryotes, comprising the red and green algae and the land plants, together with a small group called the glaucophytes. The plastids of all of these organisms are surrounded by two membranes, suggesting they developed directly from endosymbiotic...

. However, the relationships between 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 that they may be similar to the original alga type that led to green plants and red algae.

Characteristics

The chloroplast

Chloroplast

Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...

s of glaucophytes are known as cyanelles. Unlike plastids in other organisms they have a peptidoglycan

Peptidoglycan

Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria , forming the cell wall. The sugar component consists of alternating residues of β- linked N-acetylglucosamine and N-acetylmuramic acid...

 layer that is believed to be a relic of the endosymbiotic

Endosymbiotic theory

The endosymbiotic theory concerns the mitochondria, plastids , and possibly other organelles of eukaryotic cells. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts...

 origin of plastids from cyanobacteria. Glaucophytes contain the photosynthetic pigment chlorophyll a

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. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary...

. Along with red algae and cyanobacteria they harvest light via phycobilisome

Phycobilisome

Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.- General structure :Phycobilisomes are protein complexes anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated...

s, structures consisting largely of phycobiliprotein

Phycobiliprotein

Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae that capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores...

s. The green algae and land plants have lost that pigment.

Glaucophytes have mitochondria

Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...

 with flat cristae, and undergo open mitosis

Mitosis

Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...

 without centriole

Centriole

A Centriole is a barrel-shaped cell structure found in most animal eukaryotic cells, though it is absent in higher plants and most fungi. The walls of each centriole are usually composed of nine triplets of microtubules...

s. Motile forms have two unequal flagella, which may have fine hairs and are anchored by a multilayered system of microtubule

Microtubule

Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...

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

Genera

There are only 13 species of glaucophytes known, none of which is particularly common in nature. The three included genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 are:

• Glaucocystis is non-motile, though it retains very short vestigial flagella, and has a cellulose
  Cellulose
  Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
  
  wall.
• Cyanophora is motile and lacks a cell wall.
• Gloeochaete has both motile and non-motile stages, and has a cell wall that does not appear to be composed of cellulose.